"Evidence that shows or tends to show a defendant has committed a prior crime generally is inadmissible to prove the crime charged." Guill v. Commonwealth, 255 Va. 134, 138, 495 S.E.2d 489, 491 (1998). "This is because such evidence confuses one offense with the other, unfairly surprises the defendant with a charge he is unprepared to meet, and, by showing that the defendant has a criminal propensity, tends to reverse his presumption of innocence of the crime on trial." Lewis v. Commonwealth, 225 Va. 497, 502, 303 S.E.2d 890, 893 (1983). Although evidence of other crimes is not admissible when offered merely to show the accused's propensity for such crimes or acts, see Kirkpatrick v. Commonwealth, 211 Va. 269, 272, 176 S.E.2d 802, 805 (1970), it is admissible when it is "relevant to an issue or element in the . . . case." Sutphin v. Commonwealth, 1 Va. App. 241, 245, 337 S.E.2d 897, 899 (1985). Thus, evidence of other crimes is allowed when it tends to prove motive, intent, or knowledge of the defendant. Among other exceptions, evidence of other crimes also is allowed if relevant to show the perpetrator's identity when some aspects of the prior crime are so distinctive or idiosyncratic that the fact finder reasonably could infer that the same person committed both crimes. Guill, 255 Va. at 138-39, 495 S.E.2d at 491. When offered to prove identity, the prior crime does not have to be a "signature" crime; however, it must show "'a singular strong resemblance to the pattern of the offense charged.'" Spencer v. Commonwealth, 240 Va. 78, 90, 393 S.E.2d 609, 616 (1990); see also Chichester v. Commonwealth, 248 Va. 311, 448 S.E.2d 638 (1994), cert. denied, 513 U.S. 1166, 130 L. Ed. 2d 1095, 115 S. Ct. 1134 (1995).