Chris said something which the witnesses could not hear. His assailant became angrier. Chris then said something that made him even more furious. He jammed the knife into Chris's chest.
There's "evil," and then there's turning a mugging into getting knifed in the chest. Unless you're saying that this was the norm for SF muggings in the 80's. It's pretty likely that 22 year-old guy acted smart. That doesn't make it right, all I said was that I'd be interested in what exactly he said to provoke the response.