Sadly, because this was a made-for-TV movie, it rarely pops up anymore. This is one I need to see again.
I remember seeing this when it first came out in the 70s and seeing a disclaimer that it was "based on real events." The "real event" enacted in the movie was gruesome murder of Kitty Genovese in the early 1960s in New York City. The fact that more than a dozen people witnessed the murder, either visually seeing it or hearing Genovese's cries for help, but did not summon for help or assist the police in her investigation, became a stark picture of big-city indifference, the divide between Manhattan and the Outer Boroughs and even, a picture of homophobia (Genovese was reportedly a lesbian).