*72 OPINION
A jury convicted Julian Torres of possession of a narcotic drug, and the trial court placed him on four years’ probation. On appeal, the defendant asserts the following claims of error:
(1) The trial court improperly admitted evidence of a prior bad act;
(2) The prosecutor commented on the defendant’s post-arrest silence;
(3) Defense counsel was ineffective because he failed to object to the prosecutor’s comments on the defendant’s post-arrest silence; and
(4) The trial court should have given an instruction based on State v. Willits,96 Ariz. 184 ,393 P.2d 274 (1964), concerning the failure of the police to lift fingerprints from the physical evidence.
Because we find that the trial court erred in admitting evidence of the defendant’s prior drug use, we reverse and remand for a new trial. We consider the remaining issues should they arise again.
THE FACTS
Acting on information regarding possible drug sales, Phoenix police were observing a parking lot when they saw the defendant get into a suspected drug dealer’s car. As an undercover officer approached the driver’s side of the car, he observed the defendant hand the driver some money and the driver hand the defendant a small item. When the defendant realized the officer was approaching the car, he took the money from the driver, threw it on the floor of the car, got out and ran. He ran by a second undercover officer, Detective Rocky Franklin, who said he observed the defendant’s right hand in a clenched position. Detective Franklin chased the defendant, who, according to the detective, made a throwing motion with his clenched right hand and then continued to run with his fist unclenched. After he caught the defendant, Detective Franklin returned to the area where the defendant made the throwing motion and found a small amount of heroin wrapped in a cellophane wrapper.
After ascertaining that the defendant had been advised of his Miranda rights, Detective Franklin questioned him. The defendant denied possession of the heroin found on the parking lot, and he told Franklin he ran because he was wanted on outstanding traffic warrants.
PRIOR DRUG USE
According to Detective Franklin, after the defendant was arrested he was asked if he used heroin, and he replied that he had used it in the past but was not presently doing so. Before trial, the defense moved to preclude admission of this statement, arguing that it was irrelevant and prejudicial. At this point in time, the probable nature of the defense Torres would raise had surfaced during the course of the hearing on the voluntariness of his statements. The trial court, without any direct inquiry into the nature of the defense and without any ostensible weighing of relevance against prejudice, denied this motion, finding the evidence relevant to show that the defendant “knew what he was dealing.” At trial, Detective Franklin testified that the defendant had admitted using heroin in the past. The defendant testified that he told Franklin that he had used other drugs in the past, mostly marijuana, but not heroin.
Evidence of a person’s past crimes or acts is not admissible for the purpose of proving that he acted in conformity therewith on a particular occasion. Rule 404(b), Arizona Rules of Evidence, 17A A.R.S. However, this rule is “engrafted with well-recognized exceptions.”
State v. Mosley,
The problem with the state’s argument is the nature of the defense that Torres presented. He insisted that the heroin was not his, that he did not throw it, and that the officers planted the heroin *73 they said they found in the parking lot. There is simply nothing in the case which brings into play any issue of motive, knowledge, intent, absence of mistake, or accident. The evidence of prior use of heroin was relevant for only one purpose — to show that because the defendant had once at some unspecified time in the past used heroin, he must have been in the car for the purpose of purchasing the drug on this occasion. This is precisely what Rule 404(b) forbids. Perhaps the trial judge was not fully aware of the defense Torres would raise when he ruled that this evidence could be admitted, but once the matter was put in issue, an inquiry sufficient to make an informed ruling was necessary.
In a case very like this one, Division Two of this court succinctly explained the law on this subject. In
State v. Ramirez Enri-quez,
The question under Rule 404(b) is not whether evidence tends to establish guilt but how it tends to establish it. If it tends to show a disposition toward criminality from which guilt on this occasion is to be inferred, it is inadmissible. If it establishes guilt in some other way, it is admissible.
The court went on to say that the common plan exception “permits proof of [the defendant’s] commitment to a particular plan of which the charged crime is a part” and held admission of evidence of other sales required reversal.
Id.
at 433,
We examine the four Arizona cases we have found, which, in our opinion, most strongly support the argument that it was not an abuse of discretion to admit this testimony. Before we do, we observe that there is another problem with the admission of this evidence which bears on our discussion of these cases. Before admitting evidence of prior crimes, the trial court must weigh the probative value of the evidence against any possible prejudice to the defendant.
State v. Taylor,
In
State v. Tisnado,
In
State v. Mosley,
In
State v. Hines,
In
State v. Sullivan,
Having found error, we will reverse unless we can say beyond a reasonable doubt that the admission of the evidence had no effect on the jury’s verdict.
State v. Gamez,
*75 COMMENT ON POST-ARREST SILENCE
Detective Franklin testified that suspects sometimes run from the police because they have arrest warrants outstanding. He conceded that he may have learned of the existence of traffic warrants and said he was not sure how and when he learned this information. He was clear that immediately after the arrest, the defendant said nothing about outstanding warrants. He conceded that he may have learned this information from the defendant later.
During closing, the prosecutor argued: Torres was omitting critical things. Number one, Torres told you that he had borrowed some money from [the driver] and was repaying it. That’s number one. Number two, when he saw [the police] he ran because he had these outstanding warrants, traffic warrants____
******
We found out from [Detective] Franklin, A, he never told Franklin that the reason he ran was because, he was afraid that somebody, some police officer would catch him because of his outstanding warrants. Now, if that was the real reason he had run, when he talks to the detective right away, if he was sincere about that, wouldn’t he have told the detective that ‘Hey, look, you know, you got me, but let me explain something. The only reason I ran, because I had these outstanding warrants, and I didn’t want to get caught on the traffic warrants?’ But it doesn’t happen that way. See, the traffic warrants don’t come up until the time the arrest sheet is made out, and Rocky Franklin isn’t sure whether the defendant told them or they found out on their own. Then the defendant comes on the stand and says, ‘Oh, yeah, the reason why I ran — ’ Is that the reason why he ran? No. If it had been the reason why he ran, I am sure he would have told [Detective] Franklin.
The defendant contends that this constituted an improper reference to the defendant’s right to remain silent. Citing
Greer v. Miller,
In
Fletcher v. Weir,
The Court in
Fletcher
noted that
Doyle
is “a case where the government had induced silence by implicitly assuring the defendant that his silence would not be used against him.”
LOSS OF EVIDENCE
The defendant claims that, because the state failed to test the heroin packet for fingerprints and that evidence could have eliminated him as a suspect, the loss was material to his defense and was a denial of due process requiring reversal and dismissal of the charges. In the alternative, he argues that the trial court erred when it denied his request for a Willits instruction.
The defendant’s premise is flawed. The absence of fingerprints on the packet of heroin would not eliminate him as a suspect. While he would be free to argue that if his prints were not on the packet he *76 had never touched it, a finder of fact would be under no compulsion to accept that conclusion. We turn to a discussion of the other facets of the defendant’s argument on this issue.
Detective Franklin testified that he did not submit this packet of heroin for fingerprint analysis because, while it might be possible to do so, he had never recovered prints from this type of material in the past. He testified that the heroin could have been contaminated or destroyed in an attempt to lift prints from the cellophane packaging. Although he took no precautions in handling the cellophane to preserve prints, he testified that he did not intentionally destroy any fingerprints on it.
Viewed in one way, the police simply chose not to collect fingerprints from the cellophane packaging. Police generally have no duty to seek out and obtain potentially exculpatory evidence.
State v. Rivera,
We turn to a consideration of whether the way the police handled the cellophane amounts to a failure to preserve potentially useful evidence. Assuming that it did, the United States Supreme Court has held that a defendant is not deprived of constitutional due process entitling him to dismissal of the charge unless he can show bad faith on the part of the police.
Arizona v. Youngblood,
If that were not enough, there is some support in this record that no evidence was lost at all. Detective Franklin, in response to cross-examination by defendant’s counsel, testified that he understood that techniques exist to remove prints underneath other prints. If this is true, the defendant could have subjected the packet to fingerprint analysis had he chosen to do so without prejudice from Franklin’s handling of the packet.
Defendant argues that the trial court committed reversible error by failing to give a requested
Willits
instruction because the state was responsible for the destruction of potential fingerprints on the heroin packet, and that had the instruction been given, he might have been acquitted. “To be entitled to a
Willits
instruction, a defendant must prove that (1) the state failed to preserve material and reasonably accessible evidence that could have had a tendency to exonerate the accused, and (2) there was resulting prejudice.”
State v. Smith,
The defendant has failed to show the existence of material and reasonably accessible exonerating evidence. There was no showing that usable prints that could have been lifted from the heroin packet were destroyed by the way the police handled the evidence. The defendant could have, but did not, try to fingerprint the packet himself. Nor do we believe that proof of the absence of defendant’s prints would have materially aided his defense. The packaging medium was a poor one for obtaining prints. As we have twice already observed, had prints been sought, failure to obtain defendant’s prints would not have proved his innocence. We therefore find no abuse of discretion in the trial court’s refusal to give a Willits instruction.
*77 The sentence and conviction are reversed, and the case remanded for further proceedings consistent with this opinion.
