A New York City police officer has taken the witness stand for the prosecution at his former partner's manslaughter trial.

Officer Shawn Landau told a Brooklyn jury Tuesday that Officer Peter Liang's (lee-ANG') weapon went off without warning as they patrolled a housing project in 2014. A bullet ricocheted off a wall and fatally struck Akai (uh-KY') Gurley.

Landau testified that while Gurley's girlfriend and others tried to save him, the two officers wasted four minutes bickering over which one should report that he had fired his gun.

Lawyers for Liang say the shooting was an accident, not a crime. But prosecutors say he handled his weapon recklessly and even after he realized he'd shot an innocent man, did almost nothing to help him.