Having previously considered appellant’s conviction and the issues raised on appeal in D ’Ambrosio I, this court must now complete the review required by R.C. 2929.05(A) by independently weighing the aggravating circumstance against the mitigating factors, and determining whether the death sentence is appropriate.
*143A
We note at the outset that appellant seeks to raise several additional issues unrelated to our independent review. In his brief to this court, appellant sets forth seven propositions of law. All of the asserted arguments, with the exception of Proposition Nos. 1(B), IV, VII(A) and VTI(B), address issues that were previously advanced in D’Ambrosio I. The doctrine of res judicata establishes that “a final judgment of conviction bars the convicted defendant from raising and litigating in any proceeding, except an appeal from that judgment, any defense or any claimed lack of due process that was raised or could have been raised by the defendant at the trial which resulted in that judgment of conviction or on an appeal from that judgment.” (Emphasis added.) State v. Perry (1967), 10 Ohio St.2d 175, 180, 39 O.O.2d 189, 192, 226 N.E.2d 104, 108. See, also, Ashe v. Swenson (1970), 397 U.S. 436, 442, 90 S.Ct. 1189, 1194, 25 L.Ed.2d 469, 475. This court affirmed appellant’s convictions of aggravated murder, kidnapping and aggravated burglary in D Ambrosio I. The fact that the case was remanded to the court of appeals for re-evaluation of the death sentence in no way implicated the finality of those convictions. As such, we reject without further consideration each of appellant’s propositions of law, excluding Proposition Nos. 1(B), IV, VII(A) and VII(B).
In Proposition No. IV, appellant attacks the trial court’s sentencing opinion. He argues that the opinion is too “conclusory.” This argument was asserted in and rejected by the court of appeals in the original appeal, but appellant chose not to pursue it before this court in D Ambrosio I. Appellant’s failure to assert this argument in D Ambrosio I constitutes a waiver of any claimed error at this late date. Where an argument could have been raised on an initial appeal, res judicata dictates that it is inappropriate to consider that same argument on a second appeal following remand. See State v. Perry, supra. See, also, State v. Sneed (1992), 63 Ohio St.3d 3, 10, 584 N.E.2d 1160, 1167; State v. Greer (1988), 39 Ohio St.3d 236, 247, 530 N.E.2d 382, 396. We accordingly reject appellant’s fourth proposition of law.
Proposition No. VII(B) was similarly raised in the initial appeal to the court of appeals but not in D Ambrosio I. In this proposition, appellant attacks a provision of his kidnapping sentence as violating Crim.R. 43(A), which requires that all trial proceedings, including sentencing, take place in the defendant’s presence. The trial court originally sentenced appellant in open court to “10 to 25 years on the aggravated burglary charge and 10 to 25 years on the kidnapping charge, and sentence to run consecutively.” Thereafter, the sentencing opinion issued by the court added that appellant’s ten-year minimum term for each conviction was “to be a term of actual incarceration * * *.” Appellant’s decision not to pursue this issue in D Ambrosio I constitutes a waiver as discussed above, *144and thus precludes him from raising it at this time unless the claimed error rises to the level of plain error. “Notice of plain error under Crim.R. 52(B) is to be taken with the utmost caution, under exceptional circumstances, and only to prevent a manifest miscarriage of justice.” State v. Long (1978), 53 Ohio St.2d 91, 7 O.O.3d 178, 372 N.E.2d 804, paragraph three of the syllabus. “Plain error does not exist unless it can be said that but for the error, the outcome of the trial would clearly have been otherwise.” State v. Moreland (1990), 50 Ohio St.3d 58, 62, 552 N.E.2d 894, 899. We find the sentencing modification does not rise to the level of plain error, and therefore reject Proposition No. VII(B) as waived.
Proposition Nos. 1(B) and VH(A) each challenge the lower court’s imposition of the death penalty in light of the evidence appellant offered in mitigation. It is well settled that any errors that a trial court may have committed when weighing the aggravating circumstance against the mitigating factors may be rectified by this court’s independent review. State v. Lott (1990), 51 Ohio St.3d 160, 170, 555 N.E.2d 293, 304. We address this issue further in Part B of our opinion, infra.
B
We now turn to an independent review of the record as required by R.C. 2929.05(A). The three-judge panel convicted appellant of two counts of aggravated murder, but since each involved the same victim, the two counts merged. See State v. Huertas (1990), 51 Ohio St.3d 22, 28, 553 N.E.2d 1058, 1068. With respect to the aggravating circumstance of the murder, the evidence established beyond a reasonable doubt that the murder of Anthony Klann occurred while appellant committed the offense of kidnapping (R.C. 2929.04[A][7]).
Against the sole aggravating circumstance, appellant urges this court to recognize a variety of mitigating factors. Before discussing those factors, however, we note that the record contains the three previously missing mitigation exhibits: appellant’s high school record, a presentence investigation report, and a psychiatric report with addendum.
The facts surrounding the offense indicate that Klann was viciously murdered after being forced into a vehicle, repeatedly threatened, held at knife-point, and beaten. As such, we find that the nature and circumstances of the murder' are not mitigating.
Nothing in the record suggests that Klann induced or facilitated the commission of his murder, thereby rendering R.C. 2929.04(B)(1) inapplicable in this case. Defense counsel suggested that appellant participated in Klann’s murder because appellant was afraid of Keenan. Under this theory, appellant’s fear caused him to follow Keenan’s instruction to “finish [Klann] off.” R.C. 2929.04(B)(2) designates as a mitigating factor “[w]hether it is unlikely that the offense would have been committed, but for the fact that the offender was under duress, coercion, or *145strong provocation * * *.” The record fails to support a claim of duress or coercion in this ease. The knife Keenan used to slash Klann’s throat was provided by appellant. Not one witness testified that Keenan had threatened appellant or had exerted pressure on him to harm Klann. Appellant’s acts were a result of his own free will and, thus, R.C. 2929.04(B)(2) does not apply.
The evidence does indicate that at the time Klann was murdered, appellant was intoxicated. Appellant testified that by the early morning hours of September 24, 1988, he was “pretty drunk,” as a result of having consumed eight or nine beers and four or five shots of tequila. Other witnesses confirmed that appellant was drunk during the time in question. In certain circumstances, voluntary intoxication can constitute a mitigating factor, albeit a weak one. State v. Lawson (1992), 64 Ohio St.3d 336, 352, 595 N.E.2d 902, 914; State v. Hicks (1989), 43 Ohio St.3d 72, 80, 538 N.E.2d 1030, 1039. But, see, State v. Slagle (1992), 65 Ohio St.3d 597, 614, 605 N.E.2d 916, 931 (alcoholism, addiction and voluntary intoxication are not mitigating factors). Appellant attempts to argue very generally that he has a drinking problem, but none of the evidence presented indicates that he suffers from alcoholism. Although he had a history of binges and occasional blackouts while in the Army, appellant adduced no medical diagnosis of alcoholism, despite examination by two psychiatrists who were aware of his drinking patterns. Furthermore, neither of the psychiatrists found any evidence of a mental disease, defect or disorder. We, therefore, assign appellant’s intoxication little or no weight under either R.C. 2929.04(B)(3) (diminished capacity due to mental disease or defect) or 2929.04(B)(7) (any other relevant factor).
As to appellant’s youth, a potential mitigating factor under R.C. 2929.04(B)(4), he was twenty-six years old at the time of the murder. This court has held on several occasions that where a defendant kills at the age of eighteen or nineteen, the element of youth is entitled to little weight. See State v. Slagle, 65 Ohio St.3d at 613, 605 N.E.2d at 931; State v. Hill (1992), 64 Ohio St.3d 313, 335, 595 N.E.2d 884, 901; State v. Powell (1990), 49 Ohio St.3d 255, 264, 552 N.E.2d 191, 201. Defendant’s age of twenty-six clearly negates R.C. 2929.04(B)(4).
Appellant also introduced evidence at trial that prior to the instant offense, his only previous criminal convictions were two convictions for driving under the influence. This fact is entitled to some weight, given the terms of R.C. 2929.04(B)(5).-
Appellant urges this court to conclude that he participated in the events leading up to Klann’s death as a follower, not as an instigator, and thus R.C. 2929.04(B)(6) applies. The record does demonstrate that it was Keenan who initially commenced the search for Lewis and forced Klann into the truck. While appellant, Keenan and Espinoza each interrogated Klann, it was Espinoza who *146struck the victim with a baseball bat. Appellant did, however, confine Klann in the truck by holding a large knife within inches of his face. It was also appellant who, after Keenan cut Klann’s throat, voluntarily took the knife from Keenan, chased after the victim, and ultimately inflicted several fatal stab wounds on the victim’s chest, left wrist and right arm. Appellant clearly acted as a principal offender. The potential mitigation factor in R.C. 2929.04(B)(6), therefore, is not present. See State v. Landrum (1990), 53 Ohio St.3d 107, 125, 559 N.E.2d 710, 730.
Appellant further offered evidence of his military and work records as mitigating factors under R.C. 2929.04(B)(7). Appellant enlisted in the Army in 1981 and served until 1985, when he was honorably discharged. While in the Army, appellant graduated early from his training course, reached the grade of E-5 (sergeant) in less than three years, earned the Good Conduct and Army Achievement medals, and obtained a commendation for providing “outstanding maintenance support” to his brigade during a field exercise. Appellant also qualified as an expert with the M-16 and other firearms. The Army offered to promote appellant if he re-enlisted at the conclusion of his initial term, but he declined. Following his discharge from the Army, appellant was unable to secure employment as a mechanic, given his lack of certification. He could not afford the schooling necessary to achieve the required certification. As a result, appellant accepted a job as a gas station attendant, later becoming the station’s night manager.' Appellant next worked at Formall Rubber Co., but was fired after six weeks for “terrible absenteeism and tardiness.” Then, approximately one month before the murder, appellant accepted a position with Keenan’s landscaping business. We find that both appellant’s military record and employment history are entitled to some weight as mitigating factors.
During the mitigation hearing, appellant introduced five witnesses — his mother and four friends — to testify concerning his history, character and background. These witnesses depicted appellant as a nonviolent person and a “peacemaker.” They further described appellant as truthful, polite, respectful, caring and responsible. One witness called him “eager * * * motivated [and] bright,” although appellant’s high school record reflects a low grade-point average (1.441) and excessive absenteeism and tardiness. All five witnesses shared the belief that appellant could be rehabilitated.
Appellant made an unsworn statement to the three-judge panel in which he detailed his life, military career, job situations and his limited involvement with the law. While he acknowledged that the death of Klann was a tragic event, appellant denied any involvement with the killing, thereby raising the issue of residual doubt. Based upon the evidence established at trial, however, we have no doubt of appellant’s guilt.
*147Edward Espinoza, an eyewitness to the murder, testified against appellant pursuant to the terms of the former’s plea bargain. While Espinoza’s credibility was challenged during his testimony, the three-judge panel found his statements -to be credible as to the course of events. The weight to be given evidence and the credibility of witnesses are issues for the trier of fact to resolve, not an appellate court. State v. Waddy (1992), 63 Ohio St.3d 424, 430, 588 N.E.2d 819, 825. See, also, State v. DeHass (1967), 10 Ohio St.2d 230, 39 O.O.2d 366, 227 N.E.2d 212, paragraph one of the syllabus. We have no reason to reject the panel’s conclusion in this case, particularly in light of appellant’s own questionable credibility. According to appellant, no one — not Keenan, Espinoza or himself— had a weapon on the night that Klann was killed. The denial covered the possession of both knives and baseball bats. Three witnesses, other than Espinoza, testified that they had observed appellant with a knife, and two of those witnesses had observed Espinoza with a bat. On the whole, the evidence of guilt is convincing, and residual doubt is not an important mitigating factor in this case.
Having weighed the aggravating circumstance against the evidence presented in mitigation, we find that the aggravating circumstance outweighs the mitigating factors beyond a reasonable doubt.
C
In order to complete our review under R.C. 2929.05(A), we must consider whether the sentence of death imposed in this case is excessive or disproportionate to the penalty imposed in similar cases. This court has approved the death penalty in several cases where the sole aggravating circumstance was kidnapping. See, e.g., State v. Morales (1987), 32 Ohio St.3d 252, 513 N.E.2d 267; State v. Buell (1986), 22 Ohio St.3d 124, 22 OBR 203, 489 N.E.2d 795; State v. Maurer (1984), 15 Ohio St.3d 239, 15 OBR 379, 473 N.E.2d 768.
Perhaps the most significant cases for us to consider relative to our proportionality review in the instant action are State v. Brewer (1990), 48 Ohio St.3d 50, 549 N,E.2d 491, and State v. Fox (1994), 69 Ohio St.3d 183, 631 N.E.2d 124. In those cases, the defendants introduced mitigation evidence comparable to, but even greater than, D’Ambrosio’s. Like the appellant in this case, Brewer and Fox had clean records, histories of legitimate and gainful employment, and several favorable character witnesses. Unlike D’Ambrosio, however, both Brewer and Fox demonstrated mental problems and expressed remorse. See Brewer, 48 Ohio St.3d at 54, 549 N.E.2d at 496; Fox, 69 Ohio St.3d at 194-195, 631 N.E.2d at 133. Fox also showed a “relatively successful adjustment to pretrial confinement * * *.” Id. at 194, 631 N.E.2d at 133. Yet, in both of those cases, the aggravating circumstance of murder being committed during the course of a *148kidnapping outweighed the evidence offered in mitigation. We therefore find the sentence of death to be neither excessive nor disproportionate in this case.
Based upon the foregoing, the judgment of the court of appeals upholding the sentence of death is affirmed.
Judgment affirmed.
Moyer, C.J., Douglas, Wolff and Cook, JJ., concur. Wright and Pfeifer, JJ., dissent. William H. Wolff, Jr., J., of the Second Appellate District, sitting for F.E. Sweeney, J.