The Training Day star was shooting new movie Brooklyn's Finest in one of New York's roughest neighbourhoods when he stopped to visit a diner with cast and crew - and while he was eating, four men gunned down two victims in a barber shop.
He recalls, "It's not even a joke... it was a full-blown assassination and they accidentally killed the guy cutting his hair - it was a woman cutting his hair. It was terrible.
"I stood there, like, an actor in a movie. I kept expecting the AD (assistant director) to go, 'Cut, cut...' The police shut the block down."
Hawke admits he was questioned about the incident - but was a useless witness: "I saw a bunch of hoods - that's what I saw."