The New York Police Department says a gunman who ambushed two officers in their car told two passers-by to “watch what I’m going to do.”

Chief of Detectives Robert Boyce says 28-year-old Ismaaiyl Brinsley talked to people on the street just moments before the shooting and told them to follow him on the social media site Instagram.

Boyce said Brinsley had a criminal history with at least 19 arrests and his family told police he tried to hang himself last year.

Brinsley approached a parked squad car from behind on Saturday and opened fire, fatally striking two officers before killing himself. Hours earlier, he had shot and wounded his ex-girlfriend at her home outside Baltimore.

Boyce says Brinsley had ranted online about police and government and expressed despair about his own life.

(AP)