May statements by a defendant, elicited by the State in violation of the rule set forth in Miranda v. Arizona, 384 U.S. 436, 16 L. Ed. 2d 694, 86 S. Ct. 1602, 10 A.L.R.3d 974 (1966), be used as substantive evidence to rebut the testimony of a person other than the defendant? *572We hold they may not and reverse the judgment of the Court of Appeals. State v. Hubbard, 37 Wn. App. 137, 679 P.2d 391 (1984).
Thomas R. Hubbard was accused of shooting Peter Edwards, a heroin dealer. The murder occurred at about 10 p.m., June 1, 1981. Prior to trial, Hubbard moved to suppress any statements he may have made to the police and to his parole officer following his arrest. At the hearing on this motion, Detective Joe Sanford testified that he and Detective Jarvie had arrested Hubbard at his home at about 5:20 p.m., June 2, 1981. Sanford advised Hubbard of his constitutional rights "from a standard MIR card" as they drove to the Public Safety Building. Hubbard acknowledged that he understood his rights and told the officers that he had spent the previous night with his girl friend. At about this time, Hubbard told Detective Jarvie that "he didn't want to waive his rights, he wanted to talk to his parole officer, Diane Schneider." Verbatim Report of Proceedings, at 13.
Schneider testified that she met with Hubbard at the jail on the morning of June 3. She served him with a "parole suspension paper" and asked him why he was in jail. He replied "they [are] trying to charge [me] with killing a guy." When Schneider asked Hubbard why the police suspected him of the murder, he said that a witness had given them his name. Schneider next asked Hubbard whether he had been in the area at the time of the killing. Hubbard admitted that he had been in the area. Schneider then sketched a diagram of the murder scene and asked Hubbard to place himself at the scene. He did so. Then, in response to Schneider's question, "Well, did you see anything?", Hubbard said, "Well, I saw too much." Schneider asked for more details and Hubbard replied, "Well, can I talk to you confidentially?" Schneider then told Hubbard that his statements would not be kept in confidence. Hubbard "didn't say too much after that." Verbatim Report of Proceedings, at 19.
Schneider conceded that she did not tell Hubbard, before *573speaking with him in jail, that anything he said to her could be used against him in court. She also testified, however, that she had explained to him, about 3 or 4 months before his arrest, that she had to tell the truth in her parole reports.
At the suppression hearing, the court determined that Hubbard's initial statements to the police officers could be used in the State's case in chief. The court also ruled, however, that Hubbard's statements to Schneider had been obtained involuntarily, in violation of Miranda, and were thus inadmissible in the State's case in chief. The ruling stated that statements to Schneider could nevertheless be used "in rebuttal." The State did not introduce any of Hubbard's post-arrest statements in its case in chief.
Hubbard did not testify in the defense case in chief. However, his girl friend, Katherine Williams, testified that he spent the evening and night of June 1, 1981, at her house. According to Williams' testimony, neither he nor she left the house after about 6:30 that evening.
Over defense objections, the trial judge allowed the State to call parole officer Schneider as a rebuttal witness. She related the statements Hubbard had made to her after his arrest.
Defense counsel then called Hubbard to testify on surre-buttal. On direct examination, Hubbard testified that he had only been attempting to relate to Schneider what another inmate had told him about the killing. Under cross examination, Hubbard denied killing Edwards and said that he had been with his girl friend that night.
The jury returned a verdict of guilty and Hubbard appealed.
I
The Court of Appeals affirmed the guilty verdict by concluding that Hubbard's statements to his parole officer were not the result of interrogation by law enforcement officers nor made without prior advice of his right to remain silent. State v. Hubbard, 37 Wn. App. at 142. The appellate *574court reached this conclusion even though the State did not assign error to the trial court's Miranda ruling. Without assignment of error, the trial court's suppression ruling became the law of the case, not subject to review by the Court of Appeals. Kaler v. Puget Sound Bridge & Dredging Co., 72 Wash. 497, 499, 130 P. 894 (1913); South Hill Sewer Dist. v. Pierce Cy., 22 Wn. App. 738, 748, 591 P.2d 877 (1979). Furthermore, RAP 12.1 requires the appellate court to "decide a case only on the basis of issues set forth by the parties in their briefs." The conclusion by the suppression hearing judge that Hubbard's statements to his parole officer must be excluded stands.
II
The Court of Appeals gave "an additional ground for sustaining" petitioner's conviction. State v. Hubbard, supra at 142. It held that statements obtained in violation of Miranda can be admitted as substantive evidence to rebut testimony given by any defense witness. Hubbard, at 143-44. Approval of this novel approach would eviscerate the strong Fifth Amendment procedural safeguards established over the past 20 years.
Last term, the Miranda rule suffered its first exception when the Court ruled that the familiar warnings do not have to be administered before the suspect is asked questions prompted by a concern for public safety. New York v. Quarles, _ U.S. _, 81 L. Ed. 2d 550, 104 S. Ct. 2626 (1984). On the other hand, Miranda application was extended to misdemeanor arrests, although the Court in that case said that Miranda is not implicated by roadside questioning of a motorist detained pursuant to a routine traffic stop. Berkemer v. McCarty,_U.S__, 82 L. Ed. 2d 317, 104 S. Ct. 3138 (1984).
In Quarles, Justice Rehnquist characterized the public safety exception as an objective standard. He predicted, "[t]he exception will not be difficult for police officers to apply because in each case it will be circumscribed by the exigency which justifies it. . . . [Pjolice officers can and *575will distinguish almost instinctively between questions necessary to secure their own safety or the safety of the public and questions designed solely to elicit testimonial evidence from a suspect." New York v. Quarles, 104 S. Ct. at 2633. Justice O'Connor dissented from the majority analysis in light of the strength and clarity of the Miranda rule. "Were the Court writing from a clean slate, I could agree with its holding. But Miranda is now the law", she emphasized, "and, in my view, the Court has not provided sufficient justification for departing from it or for blurring its now clear strictures." New York v. Quarles, 104 S. Ct. at 2634 (O'Connor, J., concurring in part in the judgment and dissenting in part).
A few weeks later, in Berkemer v. McCarty, supra, the Court again reaffirmed the principle that "if the police take a suspect into custody and then ask him questions without informing him of [his] rights . . ., his responses cannot be introduced into evidence to establish his guilt." (Italics ours.) Berkemer, 104 S. Ct. at 3145.
The pretrial judge's ruling allowed admission of the defendant's statements only as permitted by Harris v. New York, 401 U.S. 222, 28 L. Ed. 2d 1, 91 S. Ct. 643 (1971). In Harris, the Court permitted impeachment of the defendant through use of the defendant's incriminating statements obtained in violation of Miranda. Accord, Riddell v. Rhay, 79 Wn.2d 248, 484 P.2d 907, cert. denied, 404 U.S. 974 (1971).1 In evidentiary terms, Harris allows impeachment by use of prior inconsistent statements, through which a defendant's credibility is attacked, by introducing a prior statement inconsistent with the defendant's in-court testimony. See ER 613. The Court of Appeals would allow the substance of any witness' in-court testimony to be contra-*576dieted by illegally obtained statements of the defendant. This impeachment by contradiction actually constitutes rebuttal evidence. It falls within no exception to the hearsay rule. Jacqueline's Wash., Inc. v. Mercantile Stores Co., 80 Wn.2d 784, 788, 498 P.2d 870 (1972); Anderson v. Dobro, 63 Wn.2d 923, 389 P.2d 885 (1964). To be admissible, such extrinsic evidence must be independently competent and must be admissible for a purpose other than that of attacking the credibility of the witness. Jacqueline's, at 789.
The jury in Harris was specifically instructed that it could consider the defendant's prior inconsistent statements "only in passing on [his] credibility and not as evidence of guilt." Harris, at 223; Berkemer v. McCarty, 104 S. Ct. at 3145 n.9. In upholding this limited use of the defendant's statements, the Court noted that the prosecution had done "no more than utilize the traditional truth-testing devices of the adversary process": confronting a witness with his own "prior inconsistent utterances." Harris, at 225, 226.
Since Harris, the Supreme Court has been careful to state its holding as applicable only under the circumstances present in that case. In Oregon v. Hass, 420 U.S. 714, 723, 43 L. Ed. 2d 570, 95 S. Ct. 1215 (1975), the Court noted that excluding the defendant's statement "would pervert the constitutional right into a right to falsify free from the embarrassment of impeachment evidence from [his] own mouth." (Italics ours.) The Court described Harris similarly in United States v. Havens, 446 U.S. 620, 626-27, 64 L. Ed. 2d 559, 100 S. Ct. 1912 (1980). The Havens Court felt, however, that the government should not be precluded from using a defendant's prior inconsistent statements to impeach the defendant's own testimony elicited during cross examination. The "incremental" deterrent effect of such a bar was thought to be outweighed by the need to discourage perjury. Havens, 446 U.S. at 627. The Havens decision to apply the Harris exception to a defendant's cross examination testimony is as far as the Court has gone.
As the dissent below stated, "the majority's intention in *577Harris was to open the door but a crack to permit the utilization of the inadmissible statements in the narrow context of impeaching the credibility of a testifying defendant." State v. Hubbard, supra at 155 (Ringold, J., dissenting). Affirmance of the Court of Appeals would rip the door from its hinges.
The District of Columbia Circuit Court recently rejected the rule adopted by the Court of Appeals below. The defendant in United States v. Hinckley, 672 F.2d 115 (D.C. Cir. 1982) was arrested shortly after shooting the President and three other persons. FBI agents questioned him, in violation of Miranda, and obtained statements potentially useful to rebut an anticipated insanity defense. The government argued that, even if the statements could not be used in its "case-in-chief," they should nevertheless be admissible "in rebuttal," to counter whatever psychiatric evidence the defendant might present.
The court rejected a "testimony-by-proxy" theory the government advanced to counter the expert psychiatric witnesses put on by the defense. Instead it restricted the Harris rule to impeachment of the defendant only.
Although it is indeed true that if a defendant takes the stand and testifies in a manner contradicted by illegally obtained evidence, that evidence can be used for the limited purpose of impeachment, there is as yet no basis in law for converting this limited exception into a general license to use illegally obtained evidence for rebuttal purposes. And if there were, the government does not adequately explain why it would single out the insanity defense for application of the testimony-by-proxy theory. All defense testimony is in a sense testimony by proxy, yet the government concedes that it would not seek to apply its rebuttal theory to an alibi or other affirmative defenses. We can find no reason for such a distinction.
(Footnotes omitted.) Hinckley, at 134.2
*578If the Division One holding were here accepted, statements obtained in violation of Miranda could become tantamount to guilty pleas. The defendant could not call any witnesses without opening the door, on rebuttal, to the admission of his pretrial statements. Such a rule would tell the police that they may freely interrogate an accused incommunicado and without counsel and know that statements they obtain may be used if the defendant offers witnesses in his behalf. Because such a result would effectively eliminate the constitutional guaranties embodied in the Fifth Amendment, we reverse and remand for a new trial.
Williams, C.J., Brachtenbach, Dore, and Pearson, JJ., and Cunningham, J. Pro Tern., concur.
Three states have refused to adopt Harris following analysis under their respective state constitutions. People v. Disbrow, 16 Cal. 3d 101, 113, 545 P.2d 272, 280, 127 Cal. Rptr. 360, 368 (1976) (relying on Cal. Const. art. 1, § 15); State v. Santiago, 53 Hawaii 254, 265-66, 492 P.2d 657, 664 (1971) (relying on Hawaii Const. art. 1, § 8); Commonwealth v. Triplett, 462 Pa. 244, 249, 341 A.2d 62, 64 (1975) (relying on Pa. Const. art. 1, § 9).
Here, the State seeks to employ illegally obtained statements to rebut not an insanity defense, but alibi testimony. The prosecution in Hinckley conceded it would not attempt to use the statements for an alibi defense.