Trivia: During the protracted 11-minute car chase scene between the Ford Mustang and Dodge Charger, we repeatedly see a number of the same incidental cars in background traffic. For examples: In addition to the green VW Beetle that magically reappears in several nonsequential shots, the same white 1968 Firebird also repeatedly appears (as many times as does the Beetle), and the same lavender Cadillac nearly collides head-on with the Charger at two different points in the chase. This is mainly because many of the shots had up to 8 cameras shooting from different angles, and there was a lot of redundant footage. So, the same cars noticeably kept popping up time and again (and the Charger somehow threw 7 or 8 hubcaps). These were all blatant editing problems; however, strangely enough, Bullitt still won the 1969 Academy Award for Film Editing. Go figure.
Trivia: The famous car chase took three weeks to film, and lasts 10 minutes and 53 seconds.
Answer: Notice: Aprea is credited as "Killer", not "The Killer." I think this confuses reviewers, as they assume he must be one of the hit men. However, the hit men are credited as "Phil" (Bill Hickman) and "Mike" (Paul Genge). Genge is much older than Aprea and Aprea does not look like the grey-haired hit man, as another contributor has pointed out already. There is no other killer in the plot. Perhaps Aprea's scenes were cut.