Kitty Genovese would have been 74 today. Her killer, Winston Moseley, is still alive, althought the parole board keeps turning his requests down (most recently a year ago).
A lot of research was done after her death - how on earth could 38 people stand by not just while she was attacked, but also when the attacker comes back later to deliver the coup de grace? 38 people is a platoon, for crying out loud.
Diffusion of Responsibility happens when something needs to be done, and there are clearly a large number of people who could do it. The more people, the smaller the chance that anyone will step forward to do what needs to be done.
You get paradoxical results, where people will allow something to happen that they would never have let happen if they had been there alone. A lot of big organization paralysis (the Dilbert Syndrome) can be explained with this.