Sometimes the similar way that two or more crimes are committed supports the conclusion that they were each committed by the same person. Although identity cases are resolved using the general similar fact evidence rule described above, the Supreme Court of Canada in R. v. Arp provided extremely formalized suggestions for analyzing such cases.
Two inquiries must be undertaken before this kind of similar fact evidence can be admitted. First, the judge is to "assess the degree of similarity demonstrated by the manner in which the acts in question were committed to determine whether it is likely the same person committed the alleged similar acts."139As the Court noted, "[g]enerally . . . a high degree of similarity between the acts is required . . . . The similarity between the acts may consist of a unique trademark or . . . a series of significant similarities."140It is important to remember that in answering the predicate question of whether the same person likely committed both acts, the focus must be on the acts themselves and not on other evidence of the accused’s involvement in those acts. As explained, the probative value of the similar fact inference turns on similarity between the events, not on other evidence.141The case of the lipstick robber described earlier in this chapter would pass this part of the test for admission because the "unique trademark" employed by the robber renders it unlikely that different persons would, by coincidence, be acting in this same unusual fashion. By contrast, in R. v. Trochym, proof that the accused had in the past banged aggressively and incessantly on the door of another girlfriend after their relationship ended, was too generic to yield the "improbability of coincidence" required to enable the trier of fact to infer that it must have been Trochym who was heard knocking on the door of his deceased former girlfriend the day she died.142Although on the outer edge of admissibility, the Arp case itself illustrates how even a series of "significant similarities" short of a "unique trademark" can, on the basis of coincidence reasoning, establish that
the same person likely committed both offences. The facts were these. Approximately three and one-half years apart, two lone, young, intoxicated females went missing in the early-morning hours. Each was transported to a remote location near Prince George, B.C. Each was killed and left naked. In each case the victim’s clothes were...