More than two years after the New York City police officer Brian Moore was fatally shot while on patrol in Queens, his fellow officers relived that night, as testimony began on Monday in the trial of the man prosecutors say killed him with two bullets to the head from a silver revolver.

With the slain officer’s mother and father listening, officers who were on the scene testified in State Supreme Court in Queens, recounting the events of May 2, 2015, of watching as the young officer was shot and trying to save him.

Officer Moore’s partner, Erik Jansen, described how a routine patrol in Queens Village turned deadly. Officer Moore pulled the car up alongside a man who appeared to be trying to evade the officers’ sights and asked the man what he had on him.

Seconds later, three shots rang out.

They both ducked, Officer Jansen said, and he dove from the car, rolling onto the gravel outside. While on the ground, he radioed for help. When he stood up, he saw his partner slumped toward the passenger side, unresponsive. He took off his shirt, he said, and held it to the back of Officer Moore’s head. “I kept trying to tell him to wake up,” he explained to the jurors and the prosecutor, Daniel Saunders.