Chilling New York City surveillance video shows a woman walk up behind a Brooklyn mom, pull out a handgun and shoot her in the back of the head on a crowded street, according to the NYPD.

Police identified the victim as Delia Johnson, a 42-year-old who can be seen leaning against a railing and talking to a group of people on a front stoop in Crown Heights in the moments before her slaying.

A police source said investigators have a possible suspect ID but have not yet made an arrest.