writing for the Court on the issues affecting guilt or innocence, and CARDINE, Justice, writing for the Court on the issues affecting the imposition of the capital sentence.
MACY, J., filed an opinion dissenting in part and concurring in part.
URBIGKIT, J.,- filed an opinion dissenting in part and concurring in part.
THOMAS, J., filed an opinion dissenting with respect to the reversal of the capital sentence, in which BROWN, C.J., Ret., joined.
In this appeal from the denial of post-conviction relief in a capital murder case, the issues divide, as does the pertinent statute, between those matters that affect the determination of guilt or innocence and those that impact the imposition of the capital sentence. Because of a division of the court with respect to the disposition of this case, with three justices agreeing that Roy Lee Engberg (Engberg) was lawfully convicted of first degree murder but one of those justices agreeing with the other two that the capital sentence should be set aside, the majority opinion of the court with respect to those issues affecting guilt *73or innocence has been assigned to Justice Thomas and the majority opinion of the court with respect to the issues affecting the imposition of the capital sentence has been assigned to Justice Cardine.
THOMAS, Justice (on the question of guilt or innocence of first degree murder).
The first function of the court in this appeal is to apply our rule of procedural waiver. Next, questions that could not be presented on direct appeal or for which cause exists to avoid procedural waiver must be examined for error of constitutional magnitude. With respect to the conviction of the crime of first degree murder, these questions include: failure of the prosecution to advise Engberg of a hypnotic session with a key witness; á claim of ineffective assistance of counsel on direct appeal (this issue requires that we afford incidental attention to two other contentions); a claim of cumulative error that was prejudicial to Engberg's right to a fair trial; a charge of conflict of interest because a member of the attorney general’s legal staff had served as counsel for Engberg on his direct appeal; and a claim that this court has structured an unfair and constitutionally infirm process for seeking post-conviction relief. All but five of the claims asserted by Engberg as fatally affecting his conviction fall under the rule of procedural waiver. With respect to the others, we conclude that none serve as a ground for setting aside the conviction of first degree murder. We affirm the dismissal by the trial court of Engberg’s petition for post-conviction relief insofar only as that dismissal relates to the propriety of his conviction.
Engberg was convicted, after a trial by jury, of the crimes of felony murder in violation of § 6-4-101(a), W.S.1977, and armed robbery in violation of § 6-4-402, W.S.1977. Following these findings of guilty, the jury received evidence with respect to whether capital punishment should be imposed and, in accordance with § 6-2-102, W.S.1977 (June 1983 Repl.), found five statutory aggravating circumstances and no statutory mitigating circumstances, but did determine, as a non-statutory mitigating circumstance, the fact that the crimes may have been induced by economic and family conditions. The jury then recommended capital punishment, which was imposed by the court pursuant to § 6-2-102(f), W.S.1977 (June 1983 Repl.). A sentence of twenty-five to thirty years was imposed for the aggravated robbery. Eng-berg appealed the judgment and sentence for these crimes, and this court affirmed. A more detailed statement of the facts underlying Engberg’s conviction can be found in Engberg v. State, 686 P.2d 541 (Wyo.1984), cert. denied 469 U.S. 1077, 105 S.Ct. 577, 83 L.Ed.2d 516 (1984).
After this court affirmed his convictions and denied his petition for rehearing, counsel was appointed for Engberg to assist him in presenting a petition for post-conviction relief. Engberg asserted twenty issues to the district court in support of his petition for rehearing. The State of Wyoming moved to dismiss the petition pursuant to Rule 12(b)(6), W.R.C.P. Following oral argument, the trial court entered a memorandum of findings of fact and conclusions of law explaining its decision to grant the State’s motion. An order was entered in the district court dismissing Engberg’s petition for post-conviction relief. This appeal is taken from that order.
For the sake of completeness, all of the issues asserted by Engberg are set forth in Appendix I to this opinion. Our examination of those issues convinces the court that all but six of them could, or should, have been raised on direct appeal, and no good cause is shown in this appeal for the failure to include them in the direct appeal. We have said:
“ * * * This court has taken a disciplined approach to post-conviction relief, pointing out that it is not a substitute for the right of review upon appeal from a conviction nor is it to be treated as an appeal. Questions which may be raised by a motion for post-conviction relief are limited to those of constitutional magnitude which manifest a miscarriage of justice. Those issues which could have been presented on appeal are not open to *74challenge by a motion for post-conviction relief because they are foreclosed by the doctrine of res judicata.” Cutbirth v. State, 751 P.2d 1257, 1261 (Wyo.1988) (citations omitted).
This is a rule of procedural waiver very like that applied in the federal courts.
« * * * convicte(j person is foreclosed from raising in a post-conviction proceeding any claim of error which he could or should have presented on appeal unless he demonstrates good cause for not presenting the issue on appeal and actual prejudice arising from the failure to present it. This adoption of a rule parallel to the rule applied in the federal courts will facilitate in a material way the task of the federal courts in examining issues raised in federal post-conviction proceedings in which review is sought of a conviction in the State of Wyoming.” Cutbirth, 751 P.2d at 1262.
This rule of procedural waiver is applicable to, and forecloses from direct consideration, the first issue and the third through the fifteenth issues set forth in the appendix.
The remaining issues as articulated by Engberg are:
“2. Whether the State’s failure to disclose its use of hypnosis as means of enhancing Kay Otto’s memory violated its ethical obligations and denied appellant his right to due process of law, his right of confrontation, and his right to effective assistance of counsel.
# * * * * *
“16. Whether appellant’s right to be free from cruel and unusual punishment and to due process was violated by the jury’s finding as aggravating circumstances that the murder was committed for pecuniary gain and while the defendant was engaged in the commission of a robbery when the robbery had already been used to elevate the crime to capital murder.
“17. Whether the cumulative nature of the error is such that, regardless of the harmlessness of any one error, together they prejudiced appellant’s rights to due process, fundamental fairness, and a reliable determination that the death penalty should be imposed.
“18. Whether appellant was afforded effective assistance of counsel during his appeal to the Wyoming Supreme Court.
“19. Whether it was improper for the office of the Attorney General to represent the State in post-conviction proceedings to urge that an Assistant Attorney General’s proper representation was a procedural bar to the issues raised in appellant’s petition for post-conviction relief.
“20. Whether this Court’s discussion and holding in prior cases with regard to petitions for post-conviction relief ignore the plain and obvious statutory language and establish a procedure which is viola-tive of fundamental fairness due process and equal procedure and whether it has established a confusing and unworkable process wherein courts simply dismiss petitions for post-conviction relief to get rid of them.”
The State of Wyoming styles these issues as arguments and, responding first to “Issue 20,” states them as follows:
“I. Was there error in the procedures followed in the lower court on Engberg’s petition for post-conviction relief?
* * * * * *
“VIII. Was Engberg deprived of a fair trial, due process or confrontation by the failure of the State to disclose Kay Otto’s contact with a hypnotist?
******
“XIII. Was the jury properly instructed as to statutory aggravating circumstances; was Engberg denied due process or subjected to cruel and unusual punishment?
“XIV. Did Engberg receive effective assistance of counsel on appeal?
“XV. Does the cumulative nature of any errors in this case warrant relief?
“XVI. Is the Attorney General’s entire staff disqualified from post-conviction proceedings because one of Engberg’s four attorneys on direct appeal has since become an Assistant Attorney General?”
*75Engberg urges with respect to these issues that error was committed during or after his direct appeal or that he has demonstrated good cause for not presenting the issues at that time. We agree that Issues 18,19 and 20 quoted above could not have been raised on direct appeal. We conclude that good cause has been demonstrated to avoid the rule of procedural waiver with respect to Issues 2 and 16. As to the former, the prosecutor did not disclose the hypnotic session to Engberg, and it was not discovered until after his direct appeal. With respect to Issue 16, it is premised upon recent federal decisions which would require a conclusion that Eng-berg’s sentence was imposed in violation of the Constitution of the United States of America, if we should accept the principles found in those cases. The change in the law demonstrates sufficient cause to avoid our rule of procedural waiver. Finally, the claim of cumulative error will be considered, but only with respect to those issues properly before the court in this appeal.
We first address Engberg’s claims relating to the hypnosis of a key witness, Kay Otto, the victim’s sister, who was with the victim when he was shot and killed by Engberg. We are satisfied that good cause has been demonstrated for not presenting this issue on appeal, and error must be found for violation of the standards set forth in our precedents. Even though some of our state standards were articulated subsequent to Engberg’s conviction, he would have been entitled to invoke them because his case had not been decided finally at the time those rules were promulgated. We conclude, however, that this error does not require that post-conviction relief be granted because Engberg has not demonstrated substantial prejudice.
The record now discloses that a hypnotic session was conducted in an effort to enhance Kay Otto’s recollection of the events at the time her brother was killed. This information was not disclosed to Engberg or his counsel prior to the return of the jury’s verdict and, in fact, was not discovered until the preparation of Engberg’s petition for post-conviction relief. When the question was raised, the district court permitted interrogatories to be filed and, in response, the State admitted the hypnotic session. By the affidavits of Kay Otto and the police officer who conducted the hypnotic session, the State suggests that the hypnosis was unsuccessful. Engberg contends that an evidentiary hearing must be conducted in order to resolve that question. We are satisfied that no hearing is required because, under our case law, any attempt to hypnotize a witness must be disclosed.
The State relies upon language from Haselhuhn v. State, 727 P.2d 280, 284 (Wyo.1986), cert. denied 479 U.S. 1098, 107 S.Ct. 1321, 94 L.Ed.2d 174 (1987), in which the court stated:
“ * * * [T]he State must advise the defendant of the fact that a witness has been previously hypnotized and make available to the defendant on request all statements and proceedings relating to the hypnosis.”
See also Gee v. State, 662 P.2d 103 (Wyo.1983); Chapman v. State, 638 P.2d 1280 (Wyo.1982). The State insists that this language reaches only situations in which the witness actually was hypnotized. In Chapman, however, we articulated the proposition that the fact or degree of hypnosis is difficult to evaluate. We are satisfied that a defendant need not depend upon the conclusion of the State with respect to that fact. We never have suggested that the requirement of disclosure is dependent upon the success of the effort at hypnosis. See Haselhuhn; Pote v. State, 695 P.2d 617 (Wyo.1985); Chapman.
We also are satisfied that Engberg was entitled to claim the benefit of this disclosure requirement. He was convicted on December 20,1982. Our decision in Gee was announced on April 28, 1983. While we suggested in that decision that the rule articulated was implicit in Chapman, which did antedate Engberg’s conviction, we do not rely upon the proposition that the State was on notice by virtue of Chapman. Engberg was entitled to the benefit of the rule announced in Gee because it must be applied retroactively.
*76In Ostwald v. State, 538 P.2d 1298 (Wyo.1975), we adopted the principles set forth in Stovall v. Denno, 388 U.S. 293, 87 S.Ct. 1967, 18 L.Ed.2d 1199 (1967), in order to determine whether a defendant should receive the benefit of retroactive application of a decision by this court.1 We applied those principles, as they should be applied in this case, when we said in Flores v. State, 572 P.2d 746, 747 (Wyo.1977):
“Where the purpose served by the ruling would be to ‘substantially improve the accuracy of the fact finding process at trial’ a retroactive application of such decision is mandated, United States v. United States Coin & Currency, 401 U.S. 715, 91 S.Ct. 1041, 1046, 28 L.Ed.2d 434 (1971) * *
Essentially, this is the rule advanced in Solem v. Stumes, 465 U.S. 638, 104 S.Ct. 1338, 79 L.Ed.2d 579 (1984); United States v. Johnson, 457 U.S. 537, 102 S.Ct. 2579, 73 L.Ed.2d 202 (1982); Hankerson v. North Carolina, 432 U.S. 233, 97 S.Ct. 2339, 53 L.Ed.2d 306 (1977); Williams v. United States, 401 U.S. 646, 91 S.Ct. 1148, 28 L.Ed.2d 388 (1971). In such an instance, neither good faith reliance on the old law nor the impact on the administration of justice are sufficient to require only prospective application. Williams. The product of our decisions concerning hypnosis is that the rule does enhance the fact finding process because of its utility in testing the credibility of the witness.
Furthermore, retroactive application is not foreclosed on grounds that Engberg’s case was “finally decided.” E.g., Flores, 572 P.2d 746; Ostwald, 538 P.2d 1298. Our rule with respect to “finally decided” cases relates to the availability of appeal after the judgment of conviction has been rendered. When appeal has been exhausted, we hold the case to have been “finally decided.” Flores; Ostwald. See also Clenin v. State, 573 P.2d 844 (Wyo.1978), confirmed on reh’g sub nom. Summers v. State, 731 P.2d 558 (Wyo.1989) (rule enunciated in Doyle v. Ohio, 426 U.S. 610, 96 S.Ct. 2240, 49 L.Ed.2d 91 (1976), applied retroactively to cases on direct appeal). Because Engberg’s appeal had not been decided at the time we decided Gee, 662 P.2d 103, Engberg should receive the benefit of the rule announced in Gee.
Even in light of these principles, our examination of the record persuades us beyond a reasonable doubt that this error was not prejudicial. There is no reasonable probability that the jury’s verdict would have been different had the use of hypnosis with respect to Kay Otto been disclosed. This is not an instance in which she was the only witness who identified Engberg; several other witnesses testified that he was the murderer. In addition, the record contains an abundance of circumstantial evidence linking Engberg to the robbery and the murder. On the day of the murder, he inexplicably departed from Casper where the murder occurred; he had acquired money on that day, but the source of those funds is unexplained; he paid his overdue rent and rent for a week in advance even though he abandoned the rented premises that same day; he used aliases to conceal his identity; he was deceptive with respect to the purpose for which he purchased a used car in Rawlins after the car driven from Casper failed; material evidence was found along the road between Rawlins and Salt Lake City, Utah; at various times, Engberg, or his wife, had pawned a .38 caliber revolver; a round of ammunition which would fit that revolver was discovered in the pocket of a vest in the abandoned mobile home; additional rounds were located in Engberg’s motel room when he was arrested; and, in the automobile purchased in Rawlins, an orange-toned, multicolored ski cap and a brown lightweight jacket similar to those worn by the killer were found. See Engberg, 686 P.2d 541. Under these circumstances, the loss of the oppor*77tunity to impeach Kay Otto with respect to the use of hypnosis could not lead to any different result.
We also address Engberg’s argument that the failure to disclose the use of hypnosis constituted a violation of his right to due process as announced in Brady v. Maryland, 373 U.S. 83, 83 S.Ct. 1194, 10 L.Ed.2d 215 (1963). Brady requires the state to disclose “evidence that is both favorable to the accused and ‘material either to guilt or punishment.’ ” United States v. Bagley, 473 U.S. 667, 674, 105 S.Ct. 3375, 3379, 87 L.Ed.2d 481 (1985); Brady. Impeachment evidence, like exculpatory evidence, is within the Brady rule and must be disclosed if material. Bagley; Giglio v. United States, 405 U.S. 150, 92 S.Ct. 763, 31 L.Ed.2d 104 (1972). We have stated previously that evidence of hypnosis is valuable for impeachment purposes:
“ * * * [T]he credibility of a witness could be seriously impaired by hypnosis under certain circumstances inasmuch as:
“ ‘The issue relative to the admissibility of testimony of witnesses who were previously hypnotized is whether the product of the hypnosis was to refresh or develop the witness’ own recollection or to teach the witness and add additional facts to the recollection beyond that which has been mentally stored in the memory, consciously or unconsciously. The issue is properly one for the fact finder — as are all issues relative to the credibility of the witness.’ [Chapman v. State,] 638 P.2d at 1282.
“And we carefully inquired in Chapman v. State, supra, as to whether or not the defendant had adequate opportunity to determine and present to the jury the evidence relative to aspects of hypnotism and its use on the particular witness.” Gee, 662 P.2d at 104.
See Chapman, 638 P.2d 1280; Napue v. People of the State of Illinois, 360 U.S. 264, 79 S.Ct. 1173, 3 L.Ed.2d 1217 (1959); People v. Pugh, 156 Cal.App.3d 544, 203 Cal.Rptr. 43 (1984). The failure to disclose the use of hypnosis deprived Engberg of the opportunity to effectively cross-examine an important eye witness; the jury was not privy to the use of hypnosis in weighing the credibility of Kay Otto.
The federal standard is that the failure of the prosecution to disclose evidence found to be material requires reversal of a conviction. Pennsylvania v. Ritchie, 480 U.S. 39, 107 S.Ct. 989, 94 L.Ed.2d 40 (1987). In a shift from the approach suggested in United States v. Agurs, 427 U.S. 97, 96 S.Ct. 2392, 49 L.Ed.2d 342 (1976), the Supreme Court held in Bagley, 473 U.S. 667, 105 S.Ct. 3375, that no specific request is required for disclosure of impeachment evidence. The test with respect to materiality, however, now reads:
“ * * * The evidence is material only if there is a reasonable probability that, had the evidence been disclosed to the defense, the result of the proceeding would have been different. A ‘reasonable probability’ is a probability sufficient to undermine confidence in the outcome.” Bagley, 473 U.S. at 682, 105 S.Ct. at 33.
The federal courts of appeal have considered the rule in Bagley to be retroactive. Trujillo v. Sullivan, 815 F.2d 597 (10th Cir.1987), cert. denied 484 U.S. 929, 108 S.Ct. 296, 98 L.Ed.2d 256 (1987); United States v. Ingraldi, 793 F.2d 408 (1st Cir.1986); Brogdon v. Blackburn, 790 F.2d 1164, reh’g denied 793 F.2d 1287 (5th Cir.1986), cert. denied 481 U.S. 1042, 107 S.Ct. 1985, 95 L.Ed.2d 824, reh’g denied 483 U.S. 1012, 107 S.Ct. 3245, 97 L.Ed.2d 749, cert. denied sub nom. Brogdon v. Butler, 483 U.S. 1040, 108 S.Ct. 13, 97 L.Ed.2d 802 (1987); United States v. Pflaumer, 774 F.2d 1224 (3rd Cir.1986), cert. denied 475 U.S. 1046, 106 S.Ct. 1263, 89 L.Ed.2d 572 (1986); State v. Hall, 329 S.E.2d 860 (W.Va.1985). Trial counsel for Engberg did request all statements of proposed witnesses and submitted a general request for all exculpatory evidence. These requests were granted by the trial court. We need not determine whether the request should have been understood to cover use of hypnosis to enhance the testimony of the witness. If the evidence of hypnosis was ma*78terial under the federal definition, disclosure was required. Brady; Bagley.
The reasoning which explains that there was no prejudicial error under our state rule also applies to the claim under Brady and Bagley. This conclusion is consistent with several federal cases which have found that the product of overwhelming evidence is that any evidence relating to hypnosis is not material and that no error occurred under federal standards. Trujillo; Ingraldi; Pflaumer; United States v. Risken, 788 F.2d 1361 (8th Cir.1986). Compare Bowen v. Maynard, 799 F.2d 593 (10th Cir.1986), cert. denied 479 U.S. 962, 107 S.Ct. 458, 93 L.Ed.2d 404 (1986) (identification evidence against defendant significantly impeachable by withheld evidence and case otherwise weak); Hall, 329 S.E.2d 860 (most important issue was identification testimony of a witness which was subject to impeachment by withheld evidence). This analysis under the federal standard resulting in a conclusion that non-disclosed evidence of hypnosis was not material further persuades us that the failure to disclose the hypnotic session, in accordance with Gee, 662 P.2d 103, was harmless.2
Engberg’s claim that he was denied effective assistance of appellate counsel, as advanced in his 18th stated issue, is not subject to the rule of waiver because it could not be raised in his appeal. His argument that ineffective assistance may be found because of the failure of counsel to raise every issue argued in his motion for post-conviction relief is not persuasive. The failure to raise an issue on appeal, even if meritorious, does not demonstrate ineffective assistance of appellate counsel. Cutbirth, 751 P.2d 1257. We noted in Cutbirth, 751 P.2d at 1263, that, as a matter of tactical choice, counsel presenting an appeal may choose not to raise certain issues to avoid lessening “the impact of specific issues which counsel feels offer a reasonable chance of success,” citing Jones v. Barnes, 463 U.S. 745, 103 S.Ct. 3308, 77 L.Ed.2d 987 (1983). See Kennedy v. Shillinger, 759 F.Supp. 1554 (D.Wyo.1991). We have followed the majority of the federal courts in adopting the standard articulated in Strickland v. Washington, 466 U.S. 668, 104 S.Ct. 2052, 80 L.Ed.2d 674, reh’g denied 467 U.S. 1267, 104 S.Ct. 3562, 82 L.Ed.2d 864 (1984), for the purpose of determining effective assistance of appellate counsel. Appellant must persuade us that the representation afforded to him was deficient by demonstrating errors so serious that appellate counsel could not be considered to be functioning in accordance with the constitutional guarantee and that, furthermore, the deficient performance was prejudicial to the appellant.
Because of the inherent difficulty in applying that standard, developed for evaluating the effectiveness of trial counsel, to appellate proceedings, we adopted a process in Cutbirth pursuant to which the claim of ineffective assistance of appellate counsel is resolved by the application of objective criteria. We held that ineffective assistance of appellate counsel is demonstrated by showing: first, the particular facts, as found in the trial record without resort to speculation or equivocal interference, upon which the claim of inadequate representation by appellate counsel rests; and, second, that those record facts serve to invoke a clear and unequivocal rule of law which was transgressed in a clear and obvious, not merely arguable, way. In addition, the appellant must show that he was prejudiced because the failure to present the issue on direct appeal resulted in an *79adverse effect upon some substantial right possessed by him; that is, had this court been presented the issue on direct appeal, it would have reversed the conviction.
We have weighed Engberg’s claims against this standard, and we conclude that most of his arguments do not even suggest a clear and obvious transgression of a clear and unequivocal rule. It is appropriate to consider specifically two of those claims because, arguably, they meet the standard. We shall consider Engberg’s contention that he should have been permitted to present expert testimony relating to the identification by an eye witness. We also will consider his claims relating to the exclusion of the testimony of his wife, Donna Engberg.
Engberg claims that the trial court erred in refusing to allow the testimony of an expert witness, Dr. Loftus, with respect to factors which she, and others, have identified, through experimental research, as influencing the reliability of eye witness identification. Engberg presented a memorandum to the trial court in which he advanced the following reasons for admissibility of the testimony:
“1. It will assist the trier of fact to understand the evidence or determine the facts in issue.
“2. The unreliability of eyewitness identification poses one of the most serious problems in the administration of criminal justice.
“3. The psychological facts and their effect on the witness’ credibility are clearly beyond the common knowledge of most juries.
“4. The psychological expert does not invade the province of the jury because it need not involve any opinion on the credibility of a particular witness’ testimony, but merely reviews the relevant psychological findings and enumerates the various factors affecting the reliability of eyewitness identification.”
The State of Wyoming opposed admission of the testimony by a memorandum which advanced these arguments:
“1. Such testimony is not proper subject matter for expert testimony under Wyoming law as it relates to opinion evidence in the area of common knowledge.
“2. Such testimony at best could be classified as speculation, generalization and theory.
“3. Cross-examination and argument are the proper means of dealing with eye-witness identification testimony.
“4. The testimony would be an invasion of the jury’s function to be the sole judge of the weight and credibility of evidence.
“5. Any probative value of the testimony is substantially outweighed by prejudice to the State.
“6. Any probative value of the testimony is also substantially outweighed by its tendency to mislead, distract and confuse the real issues of the case.”
The district court ruled that the testimony would not be received because it invaded the province of the jury. In addressing this claim in the post-conviction proceeding, the trial court determined that exclusion of the testimony was within its discretion and, further, that any error was harmless.
A traditional rule had been developed, prior to Engberg’s trial, that courts generally would not admit expert testimony as to the reliability of eye witness identification because that testimony either would not be helpful or would invade the province of the jury.3 More recent research seems to demonstrate that the process is more complex than earlier assumed, and some of the research findings are contrary to intuitive perceptions. See State v. Chapple, 135 Ariz. 281, 660 P.2d 1208 (1983); People v. McDonald, 37 Cal.3d 351, 208 Cal.Rptr. 236, 690 P.2d 709, 46 A.L.R.4th 1011 (Cal. 1984), and articles cited therein. Furthermore, the liberal policy reflected in Rule 702, F.R.E., which is identical to Rule 702, *80W.R.E., and the elimination of the ultimate issue rule has caused some courts to review the viability of previously accepted holdings with respect to the admissibility of expert testimony relating to eye witness identification. United States v. Moore, 786 F.2d 1308 (5th Cir.1986), reh’g denied 791 F.2d 928 (1986); United States v. Downing, 753 F.2d 1224 (3rd Cir.1985). There does appear to be a modern trend more favorable to the admission of expert testimony relating to eye witness identification. The rule still is, however, that such testimony is subject to the discretion of the trial court in any given instance. United States v. Poole, 794 F.2d 462; opinion amended, reh’g. denied 806 F.2d 853 (9th Cir.1986); Moore; United States v. Smith, 736 F.2d 1103 (6th Cir.1984), cert. denied 469 U.S. 868, 105 S.Ct. 213, 83 L.Ed.2d 143 (1984); Downing; Chapple; McDonald; People v. Beaver, 725 P.2d 96 (Colo.App.1986); Bloodsworth v. Maryland, 307 Md. 164, 512 A.2d 1056 (1986), cert. denied 548 A.2d 128 (1988); State v. Buell, 22 Ohio.St.3d 124, 489 N.E.2d 795 (1986), cert. denied, 479 U.S. 871, 107 S.Ct. 240, 93 L.Ed.2d 165, reh’g denied 479 U.S. 1000, 107 S.Ct. 609, 93 L.Ed.2d 607 (1986); State v. Moon, 45 Wash.App. 692, 726 P.2d 1263 (1986), appeal after remand 48 Wash.App. 647, 739 P.2d 1157 (1987). When we couple that specific concept with our consistent rule in Wyoming that the admission of expert testimony is within the discretion of the trial court, Price v. State, 807 P.2d 909 (Wyo.1991); Triplett v. State, 802 P.2d 162 (Wyo.1990); Brown v. State, 738 P.2d 1092 (Wyo.1987); Jahnke v. State, 682 P.2d 991 (Wyo.1984); Buhrle v. State, 627 P.2d 1374 (Wyo.1981); we must conclude that there was no transgression of a clear and unequivocal rule of law. Also, if the effectiveness of appellate counsel is evaluated in the light of the prevailing law at the time of the appeal, which is appropriate, the case law clearly favored exclusion of the testimony. Although this claim would not have been specious if raised on appeal, the failure to raise it did not constitute ineffective assistance of appellate counsel.
We also shall consider Engberg’s sixth claim of error, set forth in the appendix, under the claim of ineffective assistance of appellate counsel. In arguing that the trial court erred in permitting his wife to invoke the privilege of spousal immunity despite his waiver, Engberg contends that the privilege is that of the party spouse. He also asserts error in the exclusion of hearsay, testimony of Janet Garner, who would have testified as to earlier statements by the wife, Donna Engberg. Eng-berg’s position is that Donna’s refusal to testify made her an unavailable witness and this circumstance justified admission of the hearsay pursuant to Rule 804, W.R.E. At trial, and in its resolution of Engberg’s motion for post-conviction relief, the district court found that the spousal privilege was vested in the witness spouse. It also ruled that the proffered hearsay testimony of Janet Garner could not be received.
Early in the case, Engberg invoked his right to prevent his wife from testifying against him under the privilege of spousal immunity. When it later became apparent that certain damaging hearsay testimony concerning what Donna Engberg had stated to a police officer could be received, Engberg then waived his right to prevent his wife from testifying. It appears that this tactical decision was premised on the proposition that Engberg would benefit if Donna testified favorably to him and, if she did not, that is, if her testimony was consistent with what she earlier told the police officer, Engberg would be able to impeach her by relying upon the statements that she had made to Janet Garner.
Subsequent to Engberg’s advice to the court of his decision to waive the privilege, given in chambers, Donna Engberg was called to the stand by the State.4 We quote the ensuing dialogue from the record:
*81“MR. GUETZ: Mrs. Engberg, you are the wife of the defendant, Roy Engberg, are you not?
“MRS. ENGBERG: Yes.
“MR. GUETZ: Is it your wish to testify in this case?
“MRS. ENGBERG: No.
“MR. GUETZ: Are you willing to testify in this case.
“MRS. ENGBERG: Not if I don’t have to.
“MR. GUETZ: Mrs. Engberg, you know, that is your choice to make and we are asking you now what choice you want to make in this case, whether you want to testify or not?
“MRS. ENGBERG: No, I don’t.
“MR. GUETZ: May we approach the bench, Your Honor?
“THE COURT: You may.”
Thereafter, this discussion was conducted at the bench:
“THE COURT: Mr. Guetz, she doesn’t want to testify.
“MR. GUETZ: We can’t force her to.
“THE COURT: No, you can’t force her to.
“MR. SKAGGS: I want the opportunity to cross-examine her and assert the immunity on every question.
“THE COURT: You want what?
“MR. SKAGGS: I want the opportunity to cross-examine her and assert the immunity on every question.
“THE COURT: I don’t think if she refused to testify that — I would ask you, Mr. Guetz, to explain to her clearly that she has spousal immunity and she doesn’t have to testify.
"MR. SKAGGS: I oppose that. She does not have the privilege. Roy has the privilege.
“THE COURT: She can assert the privilege.
“MR. SKAGGS: Your Honor, under case law, it is Roy’s privilege to assert, not hers.
“THE COURT: Under the more recent rule, she can assert the immunity herself. Absolutely, she can assert that immunity on her own.
“MR. SKAGGS: Your Honor, now the prosecution is going to be in a position where they can comment on her asserting the immunity.
“MS. MILLER: If we could take a short recess. Obviously the State has had an opportunity to talk to her. Perhaps we should have the same opportunity to talk to this witness before she asserts the immunity on behalf of our client.
“THE COURT: Do you have an objection?
“MR. GUETZ: I suppose not, Your Hon- or, but she voiced what her feelings are.”
We understand the trial judge’s reference to the modern rule to reflect a misapprehension on his part that his decision was controlled by recent authority from the Supreme Court of the United States. The same position is reflected in the conclusions of law filed in connection with the denial of Engberg’s motion for post-conviction relief.
In Trammel v. United States, 445 U.S. 40, 100 S.Ct. 906, 63 L.Ed.2d 186 (1980), the Supreme Court of the United States held that a witness spouse may invoke the privilege of spousal immunity. That was said to be the rule of the federal common law and was contrary to what had been proposed as Rule 505, W.R.E., which would have limited the privilege of spousal immunity to the party spouse but was not adopted by Congress. In a similar vein, the court rejected the earlier decision of Hawkins v. United States, 358 U.S. 74, 79 *82S.Ct. 136, 3 L.Ed.2d 125 (1958), in which the court held that the privilege of spousal immunity could be claimed by both the witness spouse and the party spouse. The United States Supreme Court decisions are not controlling. Consequently, the position of the federal courts with respect to federal common law is nothing more than persuasive authority.
The rule of privilege arising out of spousal immunity is set forth in Wyoming by statute. Section 1-12-101, W.S.1977, provides:
“(a) the following persons shall not testify in certain respects:
# * * * * *
“(iii) husband or wife, except as provided in W.S. 1-12-104; * *
In the absence of the exception, this statutory provision would sound in competency, not privilege. Section 1-12-104, W.S.1977, referred to in the preceding statute, then provides:
“No husband or wife shall be a witness against the other except in criminal proceedings for a crime committed by one against the other, or in a civil action or proceeding by one against the other. They may in all civil and criminal cases be witnesses for each other the same as though the marital relation did not exist.”
This statutory language described different situations to which different rules apply. The first sentence of the statute clearly states that a husband or wife shall not be a witness against the other except in certain situations which are not found in the circumstances of this case. The second sentence provides that a husband or wife may be a witness for the other as though the marital relation did not exist. Engberg’s claim of error must be examined under the first sentence of this statute because the record is clear that his wife was called as a witness by the State. A spouse who is called as a witness by the State in a criminal proceeding perforce must be called as a witness against the defendant. The record also is clear that Engberg did not attempt to call his wife as a witness for him.
In the prior cases in which this court has considered the statute, it never has had occasion to address a situation like this. In Chamberlain v. State, 348 P.2d 280 (Wyo.1960), the wife was called as a rebuttal witness against the husband in a prosecution of the husband for statutory rape of a minor child. The court there concluded that the statute was subject to judicial interpretation; that the exception relating to a crime committed by one against the other was not limited to corporal violence against the person of the wife; and that the crime for which the defendant was prosecuted was such a special wrong and personal offense against his wife as justified her being permitted to testify. In Pike v. State, 495 P.2d 1188 (Wyo.1972), the court recognized that it would be error per se, if the husband objected, to permit a wife to testify when called by the State as a witness unless the exception found in the statute was invoked. The court also held that the error under the circumstances of that case was not prejudicial. In Simms v. State, 492 P.2d 516, cert. denied 409 U.S. 886, 93 S.Ct. 104, 34 L.Ed.2d 142 (1972), the court recognized a waiver of the privilege by the husband who was the defendant. When the claim of privilege was asserted, the trial court ruled that the State could use the transcript of her testimony at the preliminary examination, which was given prior to the marriage, if the wife did not testify. Although complaining that he was forced to so elect, the husband waived the privilege, and this court found no error. Then in Seyle v. State, 584 P.2d 1081 (Wyo.1978), the court, citing Chamberlain, held that, in a case in which the charge was first degree murder of a child, the testimony of the wife is equally available to the State and to the defendant under this statute. The husband complained, on appeal, of comment by the prosecutor upon his failure to call the wife as a witness, and the court simply held that was not plain error. The court relied upon State v. Spears, 76 Wyo. 82, 300 P.2d 551 (1956), in which the court held that it was proper to comment upon the defendant’s failure to produce the wife as a witness when she was available to him but not to the prosecution.
*83In none of these cases did the court directly consider whether a witness spouse might directly invoke the privilege if called to testify against a party spouse. Because we address the issue only with respect to the effective assistance of appellate counsel, we are limited to a determination of whether a clear and unequivocal rule of law was transgressed. In this regard, it seems fair to say that the first sentence of § 1-12-104, W.S.1977, perpetuates the common law rule of the privilege of spousal immunity in instances in which the testimony of a spouse is offered against a party spouse, although the statute, as construed, may explain the exception of what constitutes a crime against a witness spouse. See Chamberlain. We again turn to the eminent authority on rules of evidence, Professor Wigmore, relied on in Chamberlain. In 8 Wigmore, Evidence § 2241 (McNaughton rev. 1961), there is a discussion of who possesses the privilege. It begins with the recognition that the reason most commonly offered in support of this privilege, the prevention of marital dissention, results in the privilege belonging to the party only and not to the witness. It goes on:
“ * * * But taking the other suggested reason for the privilege, namely, immunity from the repugnant situation of being condemned by one’s spouse or of becoming the instrument of a spouse’s condemnation (§ 2228 supra), the privilege seems to be equally that of party and of witness. In other words, while the defendant husband is entitled to be protected against condemnation through the wife’s testimony, the witness wife is also entitled to be protected against becoming the instrument of that condemnation— the sentiment in each case being equal in degree and yet different in quality.
“The latter view seems generally to be accepted by implication underlying the various judicial utterances, but precise rulings are naturally rare and depend much on the wording of statutes. It is established in some courts that at least the privilege belongs to the party spouse against whom the other is offered as a witness. Rarely is the privilege denied to belong to the witness spouse; and rarely also is it denied to belong to the party spouse. 8 Wigmore, Evidence § 2241 at 254-55 (McNaughton rev. 1961) (footnotes omitted; emphasis in original).
A conclusion that the legislature intended to make the privilege available to both the witness spouse and the party spouse is consistent with this language. The mandatory words “shall be,” read in the light of the concept of privilege, properly can be construed to permit the witness spouse to avoid “becoming the instrument of that condemnation” even though the party spouse chooses to waive that protection. If we accept Wigmore’s description of the concept of entitlement to invoke the privilege, it certainly is arguable that the trial court correctly ruled that Mrs. Engberg could claim the privilege albeit an erroneous reason may have been advanced. Under those circumstances, we cannot discern any clear and unequivocal rule of law which was violated and, therefore, we cannot find ineffective assistance of appellate counsel for failure to assert error in the direct appeal with respect to permitting the witness spouse to claim the privilege. We agree with the trial court that Engberg was not entitled to post-conviction relief for these reasons.
To complete the examination of Engberg’s contentions in this regard, we also consider the claim of error premised upon the refusal of the trial court to admit the hearsay testimony of Janet Garner. That hearsay testimony could only be received if Donna Engberg were not available as a witness. Engberg insists that the extension to Donna Engberg of the right to claim the privilege of spousal immunity made her unavailable but, at that stage in the trial, she was unavailable as a witness only for the State of Wyoming. Even though she might have been the possessor of a privilege not to testify against Eng-berg, nothing in the statute extends a privilege to the spouse when called by the defendant in a criminal case. In order for Engberg to demonstrate unavailability to him, he had to call his wife as a witness. If she then had continued to refuse to *84testify, the court could have found that she was unavailable and the Janet Garner testimony possibly would have been admissible. In the absence of an effort to call her as a witness in his behalf, Engberg cannot assert error for the refusal of the trial court to receive the hearsay testimony.
Even assuming that Engberg was misled by the trial court and, for this reason, believed he could not call his wife as a witness on his behalf, we still could find no error in the decision of the trial court not to receive the hearsay testimony of Janet Garner. If a witness is allowed to rely upon a privilege erroneously, unavailability has been found by some courts. See United States v. McCloskey, 682 F.2d 468 (4th Cir.1982). But see United States v. Mathis, 559 F.2d 294 (5th Cir.1977); 4 D. Louisell & C. Mueller, Federal Evidence § 406 at 1029 (1985). Unavailability is only one prerequisite for receiving hearsay testimony under Rule 804(b)(6), W.R.E. See Hopkinson v. State, 632 P.2d 79 (Wyo.1981), cert. denied 455 U.S. 922, 102 S.Ct. 1280, 71 L.Ed.2d 463 (1982). As the language of the rule requires, the hearsay testimony also must be supported by circumstantial guarantees of trustworthiness. The contradictory versions of the events reported by Donna Engberg to the police officer and Janet Garner concerning Engberg’s involvement in the murder demonstrate that the circumstantial guarantee of trustworthiness was not present. There was no corroborating evidence presented which could be relied upon to enhance the trustworthiness of the version reported to Janet Garner. In the absence of the circumstantial guarantees. of trustworthiness, the hearsay testimony could not be admitted properly. See 4 D. Louisell & C. Mueller, Federal Evidence § 491, and cases cited at n. 12. For the same reason, admission of this testimony was not required in order to meet fundamental standards of due process. See Rock v. Arkansas, 483 U.S. 44, 107 S.Ct. 2704, 97 L.Ed.2d 37 (1987); Green v. Georgia, 442 U.S. 95, 99 S.Ct. 2150, 60 L.Ed.2d 738 (1979); Chambers v. Mississippi, 410 U.S. 284, 93 S.Ct. 1038, 35 L.Ed.2d 297 (1973).
Our conclusions with respect to these issues also dispose of the claim of cumulative error which Engberg asserts. See Schmunk v. State, 714 P.2d 724 (Wyo.1986); Browder v. State, 639 P.2d 889 (Wyo.1982). The result of those cases depends, of course, upon the existence of error. In this instance, we conclude that there was no error and, consequently, there is no claim to consider of the cumulative effect of trial errors. Jennings v. State, 806 P.2d 1299 (Wyo.1991); Justice v. State, 775 P.2d 1002 (Wyo.1989).
As a final matter, we turn to Eng-berg’s arguments raised in issues 19 and 20. We can see no demonstration of any prejudice to Engberg even if one could conclude that error was committed by the representation by the attorney general of the state in this action when a present member of his staff represented Engberg in his direct appeal. We can discern no way in which that alleged conflict would have been disadvantageous to Engberg in the post-conviction process. Furthermore, in Wyoming, we require something more than simply assertions of impropriety. We cannot acknowledge, without some factual showing, that a member of the attorney general’s staff who had a conflict of this nature would have any involvement in, or knowledge of, the work done on behalf of the State of Wyoming. In addition, the objective evaluation of effective assistance of counsel on appeal avoids the concern that the attorney general might involve the member of his staff who did serve as counsel for Engberg in order to insulate that staff member from the ineffectiveness accusation.
As to Engberg’s argument that the post-conviction procedure which has been adopted in Wyoming is fundamentally unfair, that argument must be advanced by someone who was disadvantaged by the process. We are satisfied that Engberg’s claims have received every consideration to which they are entitled under our statute and under the Constitutions of the State of Wyoming and the United States. If a different post-conviction procedure is to be invoked, that is a matter which must be *85addressed by the legislature. The one which is in place, as applied to Engberg, did not result in any deprivation of his constitutional rights.
Our review of the issues raised by Eng-berg in this appeal from the denial of his motion for post-conviction relief persuades this court that, with respect to Engberg’s conviction of first degree murder, we correctly held that:
“ * * * Our examination of the record and the law persuades us that there is no error with respect to any of the claims made by the appellant, * * *.” Engberg, 686 P.2d at 644.
Insofar as his guilt of the crime of first degree murder is concerned, we affirm the order of the district court dismissing Eng-berg’s petition for post-conviction relief and conclude that Engberg has exhausted any substantial state remedies.
APPENDIX I
STATEMENT OF THE ISSUES
1. Whether the Court’s refusal to permit appellant to call an expert on eye-witness identification was error which deprived appellant of his right to a fundamentally fair trial and his right to compulsory process.
2. Whether the State’s failure to disclose its use of hypnosis as means of enhancing Kay Otto’s memory violated its ethical obligations and denied appellant his right to due process of law, his right of confrontation, and his right to effective assistance of counsel.
3. (a) Whether appellant was denied due process of law by the extradition procedure used to bring him to Wyoming such that the proceedings here must be declared null and void.
(b) Whether appellant was denied due process by the introduction of evidence that he had to be beaten by the police officers who arrested him in order to prevent him from fleeing.
4. Whether the State’s introduction of evidence showing that appellant frequently used aliases denied him his right to a fundamentally fair trial.
5. (a) Whether appellant’s rights under the Fifth Amendment to the United States Constitution and Article 1, § 11 of the Wyoming Constitution were violated when evidence that he refused to wear a stocking cap so that he could be photographed was introduced at his trial and argued as evidence of guilt.
(b) Whether appellant’s right to confront witnesses was denied him by the court’s refusal to permit cross-examination of the police officer who photographed him concerning appellant’s medical condition.
6. (a) Whether a defendant’s spouse can invoke spousal privilege and decline to testify when the defendant seeks to have the spouse testify.
(b) Whether the Sixth Amendment to the United States Constitution and Article 1, § 10 of the Wyoming Constitution were violated by the trial judge’s erroneous ruling that appellant could not call Donna Engberg as a witness, cross-examine her, nor introduce her prior statements for impeachment purposes.
(c) Whether a defendant’s spouse who refuses to testify is an unavailable witness whose hearsay statements may be admitted into evidence.
7. Whether the use of a conclusive presumption to convict appellant of first degree murder is plain error and requires reversal of the conviction.
8. Whether appellant’s rights under the Fourth Amendment to the United States Constitution and Article 1, § 4 of the Wyoming Constitution were violated by the introduction of evidence seized by the police during a warrantless search of appellant’s trailer.
9. Whether the testimony of the ballistics expert was incompetent and should have been disregarded, and should be disregarded now, and thus whether there is insufficient evidence to support the conviction.
10.(a) Whether the prosecution’s use and manipulation of the press prior to appellant’s trial deprived appellant of his right to a fair trial.
(b) Whether appellant’s right to effective assistance of counsel was denied him by *86his initial court-appointed attorney’s failure to combat the prosecution’s misuse of the media.
11. Whether the trial court’s failure to excuse venireman Alberts for cause deprived appellant of his right to a fair trial by an impartial jury.
12. Whether the voir dire procedure used at appellant’s trial denied him his right to a fair trial by an impartial jury.
13. (a) Whether the introduction of evidence in the penalty phase that appellant had escaped from the authorities in Missouri denied him his right to due process and a fundamentally fair finding that the death penalty should be imposed.
(b) Whether the prosecutor’s closing argument in the penalty phase of the trial deprived appellant of his right to due process and fundamentally fair trial when the prosecutor argued appellant needed to be executed in order to restrain him and when the Wyoming Supreme Court has previously recognized that kind of argument is only proper where the heinous, atrocious, or cruel aggravating circumstance is involved.
14. Whether the court’s refusal to permit appellant the opportunity to present evidence of a mitigating circumstance, the cruelty of the manner of execution, denied appellant his right to due process of law and a fundamentally fair finding to impose the death penalty.
15. Whether appellant’s right to due process and to be free from cruel and unusual punishment was violated by the statutory presumption in favor of death under Wyoming law which requires the defendant to bear the burden of demonstrating that sufficient mitigating circumstances outweigh the aggravating circumstances so as to warrant leniency.
16. Whether appellant’s right to be free from cruel and unusual punishment and to due process was violated by the jury’s finding as aggravating circumstances that the murder was committed for pecuniary gain and while the defendant was engaged in the commission of a robbery when the robbery had already been used to elevate the crime to capital murder.
17. Whether the cumulative nature of the error is such that, regardless of the harmlessness of any one error, together they prejudiced appellant’s rights to due process, fundamental fairness, and a reliable determination that the death penalty should be imposed.
18. Whether appellant was afforded effective assistance of counsel during his appeal to the Wyoming Supreme Court.
19. Whether it was improper for the office of the Attorney General to represent the State in post-conviction proceedings to urge that an Assistant Attorney General’s proper representation was a procedural bar to the issues raised in appellant’s petition for post-conviction relief.
20. Whether this Court’s discussion and holding in prior cases with regard to petitions for post-conviction relief ignore the plain and obvious statutory language and establish a procedure which is viola-tive of fundamental fairness due process and equal procedure and whether it has established a confusing and unworkable process wherein courts simply dismiss petitions for post-conviction relief to get rid of them.”
. In Ostwald v. State, 538 P.2d 1298 (Wyo.1975), we quoted from Stovall v. Denno, 388 U.S. 293, 297, 87 S.Ct. 1967, 1970, 18 L.Ed.2d 1199 (1967), the following:
“ * * * The criteria guiding resolution of the question implicates (a) the purpose to be served by the new standards, (b) the extent of the reliance by law enforcement authorities on the old standards, and (c) the effect on the administration of justice of a retroactive application of the new standards.”
. The State has suggested that this issue should be treated under the newly discovered evidence standard articulatéd in Opie v. State, 422 P.2d 84 (Wyo.1967), as recently applied in Gist v. State, 737 P.2d 336 (Wyo.1987), appeal after remand 766 P.2d 1149 (Wyo.1988). See Lacey v. State, 803 P.2d 1364 (Wyo.1990). The fact that the evidence was not discovered because of a failure by the prosecution to follow the rule of Gee is a significant distinction. Under those circumstances, it is inappropriate to invoke the newly discovered evidence rule. See United States v. Agurs, 427 U.S. 97, 96 S.Ct. 2392, 49 L.Ed.2d 342 (1976). As quoted in Agurs, 427 U.S. at 111, "If the standard applied to the usual motion for a new trial based on newly discovered evidence were the same when the evidence was in the State’s possession as when it was found in a neutral source, there would be no special significance to the prosecutor’s obligation to serve the cause of justice."
. E.g., Dyas v. United States, 376 A.2d 827 (D.C.App.1977), cert. denied 434 U.S. 973, 98 S.Ct. 529, 54 L.Ed.2d 464 (1977); United States v. Brown, 540 F.2d 1048 (10th Cir.1976), cert. denied 429 U.S. 1100, 97 S.Ct. 1122, 51 L.Ed.2d 549 (1977); United States v. Amaral, 488 F.2d 1148 (9th Cir.1973).
. Engberg has not chosen to challenge the invocation of the privilege in front of the jury. We already have considered situations in which witnesses have invoked their own privilege not to testify because of their right not to incriminate themselves. Haselhuhn v. State, 727 P.2d 280 (Wyo.1986), cert. denied 479 U.S. 1098, 107 S.Ct. 1321, 94 L.Ed.2d 174 (1987); Hopkinson v. State, *81632 P.2d 79 (Wyo.1981), cert. denied 455 U.S. 922, 102 S.Ct. 1280, 71 L.Ed.2d 463 (1982). More recently we have reversed a conviction in a case in which the trial court permitted the prosecution to call witnesses in the presence of the jury who the court and the prosecution knew would invoke the Fifth Amendment privilege not to testify. Jones v. State, 111 P.2d 54 (Wyo.1989). In an instance such as this, as in Haselhuhn and Hopkinson, if counsel or the court is aware that the privilege may be invoked, it is far better to approach the matter in chambers. Certainly, the proceeding should be adjourned to chambers as soon as that possibility becomes apparent. Otherwise, there is a clear risk of a reversal as in Jones. We deplore the unnecessary presentation of such an issue in front of the jury because of the potential for prejudice.