concurring in part and dissenting in part:
I concur in all of the majority opinion except that portion of Section C that holds the admission of Exhibits 4-A and 22-E, if error, to be harmless. The credibility of the prosecution witnesses was very much *933in issue. The photographs, of a man identified as Todd masturbating and of a young boy’s genitals, were of a nature likely to lead a jury, in the absence of limiting instructions, to conclude that Todd is a bad man and therefore must be guilty of something.
The majority opinion concludes that Exhibit 4-A, the photograph of the man masturbating, must have been either disregarded by the jury or used to show Todd’s modus operandi in masturbating, which is a proper use. Those two possibilities, however, do not encompass the universe; the jury could simply have been adversely influenced or prejudiced by the photograph as illustrating guilty character of Todd.
Nor am I convinced that the admission of Exhibit 22-E, the photograph of a young boy’s genital area, without limiting instructions, was harmless because there was testimony that other pictures and magazines of similar nature had been found in Todd’s house. The potential of such a photograph for causing prejudice is far greater than that of mere testimony. As the prosecutor stated in his closing argument, “a picture is worth a thousand words.”
“Evidence of a person’s character or a trait of character is not admissible for the purpose of proving action in conformity therewith,” with exceptions not relevant here. Fed.R.Evid. 404(a). Similarly, “[e]vidence of other ... acts is not admissible to prove the character of a person in order to show action in conformity therewith.” Fed.R.Evid. 404(b). Exhibit 4-A, the photograph of a man identified as Todd masturbating, is clearly evidence of an “other act.” So, probably, is Todd’s possession of Exhibit 22-E, the picture of the boy’s genitals.
It is true that evidence of other acts can be admitted for purposes other than to prove character. It can be used to prove intent, Fed.R.Evid. 404(b), and modus operandi to establish identity, United States v. Perkins, 937 F.2d 1397, 1400 (9th Cir.1991). But when such acts are used for those defined purposes, a limiting instruction should be given. United States v. Min-yard, 461 F.2d 931, 934 (9th Cir.1972). None was given here. This omission was error and, in my view, prejudicial error.
Exhibit 22-E, the photograph of the boy’s genitals, was admitted to prove a mental element of child molestation, a crime of which Todd was acquitted. It was utterly unnecessary for that purpose. For the crime of child molestation, Arizona requires proof of a defendant’s unnatural sexual interest in children “in order to distinguish the criminal conduct from innocent conduct as, for example, the act of the physician in treating the child, or the parent in bathing the ‘private parts.’ ” State v. Madsen, 137 Ariz. 16, 18, 667 P.2d 1342, 1344 (App.1983). The act of child molestation with which Todd was charged was fellatio. No contention was offered, or could reasonably have been offered, by the defense that Todd’s alleged act of fellatio was performed with an innocent motive like that of a physician, or of a parent bathing a child. If the jury found that Todd had committed the act, it would have had to find from the same evidence that he demonstrated an unnatural sexual interest in children in so doing. See United States v. Hester, 719 F.2d 1041, 1043-44 (9th Cir. 1983). Indeed, Todd’s counsel conceded as much. On the issue of Todd’s state of mind, therefore, Exhibit 22-E could add nothing.
I confess that the line between circumstantial evidence of intent and improper evidence of character is often unclear, but with no limiting instruction, the danger that the photograph would be used to show bad character certainly existed. That danger was maximized by the government’s final arguments. The prosecutor never argued that Exhibit 22-E showed Todd’s state of mind. Instead, he stated that “[t]his particular photo shows that Mr. Todd was not the treasured member of the community, was not the great guy that the defense would have you believe.” After such an invitation to the jury, I am unwilling to conclude that the jury, without instructions, confined the use of the photo*934graph to (unnecessary) proof of intent.1
Exhibit 4-A, the photograph of a man identified as Todd masturbating, was also subject to question as evidence of modus operandi. “Other act” evidence may be used to establish that a defendant employed a distinct modus operandi when committing other crimes, and typically is admitted for the purpose of establishing the identity of the perpetrator of the charged crime. See, e.g., United States v. Perkins, 937 F.2d at 1400. Here, of course, the purpose was not to establish identity, but to corroborate testimony of minor witnesses that they had seen Todd masturbate.2 Nevertheless, there is good reason to require here, as in cases where identity is the issue, that the modus operandi be distinctive. See id. If there was some distinctive method of masturbation used by Todd that was testified to by the alleged victims, then a photograph of Todd using that same method would appear to be admissible and probative that the crime occurred as the alleged victims testified that it had. The difficulty with Exhibit 4-A is that the method used by Todd is not particularly distinctive. There is nothing inherently unusual about the use of a tissue while masturbating.
If Todd’s method is not at all unusual, then Exhibit 4-A is nothing more than a picture of Todd masturbating at some time. The mere fact that Todd has masturbated at some time does little to corroborate the testimony of the minor witnesses that Todd masturbated at some other time in their presence, and thus committed the crime of sexual indecency.
Despite these problems, it might have been within the discretion of the district court to admit the evidence for purposes of showing modus operandi if a limiting instruction had been given. Without it, the photograph might simply have added to the inference of bad character already raised by Exhibit 22-E.
There is one other significant consequence of the trial court’s failure to give a limiting instruction with regard to Exhibit 4-A. A proper limiting instruction would have informed the jury that, in order to take the prior “bad act” evidence into account, the jury must first find by a preponderance of the evidence that the defendant committed the prior bad act. See United States v. Marashi, 913 F.2d 724, 735 (9th Cir.1990); United States v. Miller, 874 F.2d 1255, 1268 (9th Cir.1989). There was dispute in the testimony over several identifying features in the photograph. The identification of Todd as being the male figure in the photograph was subject to question. The jury was never required to find that the person depicted was Todd before making use of the photograph. And they might have concluded that Todd’s possession of the photograph reflected on his character, no matter who was depicted.
In urging admission of Exhibit 4-A, the prosecutor argued that it was “extremely critical evidence,” because of the attacks that had been made on the credibility of the government’s witnesses. I agree, and would not find its admission without a limiting instruction, or the admission of Exhibit 22-E without a limiting instruction, to be harmless error. For that reason, I dissent *935from the majority’s ruling regarding these two exhibits, and from its judgment.
. As the majority opinion indicates in its footnote 8, there may well be another defect in Exhibit 22-E: the scientific method of establishing that the age of the person depicted was under 16 was not established or demonstrated to be reliable.
. There is considerable question whether Exhibit 4-A was truly rebuttal evidence at all. Corroboration of the facts testified to by the alleged victims would appear to be part of the government's case-in-chief. Rebuttal of the defense’s opinion testimony concerning the untruthful character and reputation of the alleged victims would normally be counter-testimony as to their character and reputation for truthfulness. See Fed.R.Evid. 608(a)(2).
The government has also contended that Exhibit 4-A was admissible as evidence to rebut defense counsel’s statement in opening argument regarding Todd's character. Rule 404(a)(1) permits rebuttal evidence on the subject of a defendant's character only when evidence of the defendant's character, such as testimony as to his honesty or good intentions, is offered by the defense. United States v. Gillespie, 852 F.2d 475, 479 (9th Cir.1988). The opening statement of Todd’s lawyer was not evidence, and no other evidence of Todd's character was offered by the defense.