NYPD officer testifies at manslaughter trial of his former partner, Peter Liang

NEW YORK (WABC) -- Testimony resumed Thursday in the trial of NYPD Officer Peter Liang, charged with manslaughter in the fatal shooting of Akai Gurley in a Brooklyn stairwell in 2014.

Liang's partner on patrol with him that night took the stand, and jurors saw the bullet that killed Gurley. Liang says he fired his gun accidentally.

Officer Shaun Landau, witness for the prosecution, was forced to testify against his former partner, Peter Liang.

"Peter was in shock," Landau told the jury. "He couldn't believe he just shot someone."

Landau and Liang were patrolling the Pink Houses in East New York, when Liang fired his weapon in a darkened stairwell. A single shot that ricocheted off the wall and into the chest and through the heart of Akai Gurley.

The panic was captured in a neighbor's 911 call.

Liang claims he fired his weapon by accident, and is on trial for manslaughter.

"Did you see a threat", asked the prosecutor. "No", Landau answered.

"Did you hear a threat?". "No".

"Did you take your gun out of your holster?" "No", said Landau.

Landau described his partner as distraught, but admitted that neither of them even tried to revive Akai Gurley, that they radioed for an ambulance and then stood by as Gurley's girlfriend unsuccessfully performed CPR.

"You didn't know what to do?", the prosecutor shouted. "You didn't know how to perform CPR?"

"I didn't feel qualified to perform CPR," said Landau.

Prosecutors insist Liang drew his weapon for no reason and fired recklessly into the stairwell, telling Landau after the shooting that he was sure to be fired over it.

"Did he say, 'I'm fired', or did he say, 'I fired'"?, asked Liang's defense attorney.

"No," Landau hit back. "He said, I'm fired."