Who killed Gwen?

[Local Hero]

I think it's been accepted in cannon now that she was dead before Gobby tossed her off the bridge (letting Peter think he had killed her was just another twist of the knife), but at the time, and for a long time after Peter did believe he had killed her.

I don't think finding out after the fact that he didn't has lessened the impact on him, it just reiterates his feeling that she shouldn't have been put in that position in the first place and the only reason she was, was because of their association.