Interestingly, while the bystander effect is a real thing -- the Kitty Genovese story doesn't really support it. As wikipedia points out in its understated way, the story that prompted all this research has "been criticized as inaccurate." There were actually very few witnesses who could have seen her murder and it's entirely possible that at least one of them did call the police.
From memory I think there were a number of calls, but the police didn't prioritise them highly enough. I think in the end it was a neighbour who ID'ed the murderer.
