Officer Peter Liang cried on the witness stand on Monday morning, breaking down as he described the moment he discovered that a bullet he fired into a dark stairwell had mortally wounded an innocent man.

“I went back to see where the bullet was. When I got down to the seventh floor I heard someone crying. I saw Mr. Gurley there at the time, and I said, ‘Oh my God, someone’s hit,’” Liang testified, before taking a short break to compose himself.

Liang told the jury that he fired because he was “startled by a quick sound.”

“It happened so quick, I couldn't say what it was.”

Liang, who is on trial for manslaughter, criminally negligent homicide, and other charges relating to the fatal shooting of 28-year-old Akai Gurley in November of 2014, was the final witness for the defense inside a packed courtroom in Brooklyn Supreme Court.

Nervous and unsteady, with Gurley’s family sitting in the gallery, Liang had to be told multiple times by the judge to speak clearly into the microphone. He began his testimony by telling the jury that he became an NYPD officer because the economy was slow when he graduated college, and he was admitted into the police academy far earlier than he expected to.

“Did you learn CPR at the police academy?” Liang’s attorney, Rae Koshetz, asked her shaken client.

“Sort of,” Liang replied, explaining that his class had been fed the answers by the police academy instructor, and had never been trained for CPR with a dummy.

Liang also admitted that he “never really touched” his firearm training manual, and that he learnt mostly about firearm safety from Powerpoint presentations.

Last week, Liang’s partner, Officer Shaun Landau, testified that Liang bickered with him over who should call their superior after he fired his errant bullet, and stalled for around four minutes before locating Gurley, who was dying in the stairwell of East New York’s Pink Houses.

Landau, who received immunity from the prosecution for his testimony, also recalled Liang’s words immediately after he fired the shot: “I’m fired.”

On cross-examination, Liang explained that he decided to call his sergeant and not to radio in the accidental firing, because he didn’t want other officers to leave their post because of his mistake.

“It wouldn’t make sense to call all the officers over to search for a bullet,” Liang testified. “I said give me your cell phone, so I could see the number of our sergeant. I dialed the phone and [Landau] took the phone away from me and put it back in his pocket.”

While trying to call his sergeant, Liang told the jury that was still unaware that Gurley had been hit by the shot.

"I didn't hear any footsteps in the stairwell. My ears were ringing, the gunshot was so loud."

Liang, who currently lives in Bensonhurst with his mother, father, cousin, and wife, claimed that he only argued with his partner for 30-40 seconds, but admitted that he said “I’m fired” after shooting his service weapon.

Liang testified that he immediately put in a radio call for backup once they found Gurley’s body, but that he was unable to get a clear answer on what the address of the building was from either Melissa Butler or Melissa Lopez, both of whom were trying to help save Gurley’s life.

“I felt the best way to get help for him was to get professional medical help,” Liang said. “I asked Ms. Butler was the address was. I was panicking so much, I couldn’t process the information.”

Liang said that after he finally transmitted the address, it was only 20-30 seconds before other officers arrived.

Liang also testified as to why he had his gun drawn in the dark stairwell: “I’ve done hundreds of verticals, and this was how I always did it. There’s never been a problem.”

The defense rested its case after Liang gave his testimony, and Judge Danny Chun set closing arguments and jury instructions for tomorrow morning.

Outside the courthouse Akai Gurley's mother, Sylvia Palmer, told a group of reporters that "saying it was accidental is not enough."

"He shows no remorse," she added.

"He murdered my son and I want justice for my son."