The problem in the case at bar is that the trial court did not inquire of, nor did the prosecutor cite, a provision of K.S.A. 60-455 for how Cook's prior conviction was admissible. The prosecutor's rationale for admitting Cook's prior conviction was that it showed that Cook was biased, that he lied about not having a place to live in Kansas as required by the conditions of his probation, and that Cook could not just get up on the stand and lie. The court did not determine whether the evidence was relevant to prove a material fact under K.S.A. 60-455 such as motive, opportunity, intent, preparation, plan, knowledge, identity, or absence of mistake or accident.. . . .The State fails to establish the relevance of Cook's prior conviction under Kansas law. His prior conviction is probative because it has a tendency to prove the fact that he knew possessing marijuana was illegal. However, his prior conviction is not material because the fact that Cook knew possessing marijuana was illegal was already established by his testimony and any other way that he knew it was illegal was not a fact that is significant under the law of the case and properly at issue. Without establishing the materiality prong of the relevance test, the trial court erred in admitting Cook's prior conviction.. . . .Evidence to impeach a witness' credibility is relevant. However, the admission of another crime to impeach a witness' credibility is governed by K.S.A. 60-421.K.S.A. 60-421 prevents the State from using a defendant's prior convictions for impeachment unless the defendant opens the door by introducing evidence that he or she is credible. A criminal defendant does not place his or her credibility in issue merely by taking the witness stand. See State v. Macomber, 241 Kan. 154, 157-58, 734 P.2d 1148 (1987) (reversing defendant's conviction because the State improperly questioned the defendant regarding prior crimes during cross-examination).The court in Macomber stated: "A defendant must have the right to deny the charges against him and to maintain that he has consistently done so without fearing such testimony will render evidence of other crimes admissible."
While there may be opportunities to use K.S.A. 60-455 evidence to impeach the credibility of the testifying witness, in Cook's case the prejudice of the evidence is overwhelming in comparison to the materiality of the evidence. Under the facts of this case, exactly how Cook knew marijuana was illegal and why he did not have a place to live in Kansas, does not open the door to evidence of Cook's prior conviction despite the ensuing credibility battle.