By the time police arrived a few blocks later, the suspect and his female friend had disembarked. The driver was oblivious of what had occurred, but police claim the bus was equipped with working security cameras.
The working description of the assailant: A man in his late teens or early 20s with a white t-shirt and blue jeans. So, you know, everyone in the city. Including you, young Marlon Brando.
Update, 9 a.m.: The San Francisco Police claim that the stabbing victim first witnessed his alleged attacker and that man's female companion argue and then have a physical fight in which the man slapped the woman. The victim claims he intervened and blows were exchanged -- the victim was "punched in the head and body." After the suspect and the woman stepped off the bus at Winston and Lake Merced along with another man in their group, the victim "soon realizes he has minor stab wounds to shoulder and waist and calls PD." The victim is a white male of 35 years. The suspects are described as Caucasian and in their 20s.