The partner of NYPD Officer Peter Liang, who is on trial for fatally shooting an innocent man in the stairwell of an East New York housing project, told a jury Tuesday afternoon that the pair spent the crucial minutes after the shot was fired arguing over who should call their superior.

“He pulled my phone out of my hand and tried to call the sergeant. I took the phone back and hung up,” Officer Shaun Landau testified in Brooklyn Supreme Court.

Around 11 p.m., after Liang fired the single shot, Landau said he repeatedly told Liang to call their superiors on his own cell phone, but Liang resisted. When Landau took out his phone to display the number to Liang, Liang grabbed the phone and tried to call their superiors from Landau’s phone.

“He was the one who had the accidental discharge. I felt he should call,” Landau testified.

While the two rookie officers bickered over who should call their sergeant, 28-year-old Akai Gurley lay dying three floors below them, Liang’s bullet having torn through his heart.

“I leaned over him in a puddle of blood and urine and I was telling him to stay with me, I’m getting him help,” Melissa Butler, Gurley’s girlfriend, testified through sobs.

The prosecution played the single 911 call from that night, placed by Butler’s neighbor Melissa Lopez, and the distraught 28-year-old identified her own voice as the one that shouted out, “he’s not breathing!”

Back on the eighth floor, immediately after the shot was fired, Landau testified that he asked Liang “What the fuck happened?” According to Landau, Liang responded, “It went off by accident,” and then, “I’m fired.”

Landau has already been given immunity by the Brooklyn District Attorney’s office, something that Liang’s defense wanted to make abundantly clear to the jury. The two counts of official misconduct that Liang is facing could easily have been applied to Landau as well, the defense pointed out.

“Did you understand what the concept of immunity was when you testified?” defense attorney Robert Brown asked Landau, referring to his agreement with the DA.

“I knew that whatever I would say could not be used against me,” the clean-shaven Landau responded.

“You never agreed to cooperate against your partner?” Brown pressed.

“No,” Landau answered.

Landau has been on modified duty since the shooting and has had his gun and shield taken away from him while he awaits administrative charges from the NYPD. He also has been named in a lawsuit by the Gurley family.

On cross-examination, the defense pointed to discrepancies between the testimony Landau had just given in court and a previous interview he had given the NYPD in the days following the shooting.

During those interviews, Landau told the NYPD that Liang had in fact used his radio to summon other officers to the scene, mentioning that there had been an accidental discharge. Landau left that information out of his testimony on Tuesday afternoon.

“You do realize he’ s [Liang] being charged with official misconduct?” Brown questioned Landau. “But he did in fact make the call as soon as he ran down. He did in fact do this.”

“Yes,” Landau responded.

Landau was accompanied by a large contingent of Patrolmen’s Benevolent Association members, the same police union that has avoided Liang for much of the trial.

Landau testified that he had graduated in the same class as Liang from the police academy in December 2013. By March 2014, the two had been assigned together in the Police Service Area 2, which served housing developments in Brownsville and East New York.

While the pair did most of their patrols together, Landau said he didn’t socialize with Liang outside of the NYPD. On the night of the shooting in November of 2014, it was only their second time working in the Pink Houses.

The officers were taking part in “Operation Impact,” a now-defunct policing strategy that sent rookie cops to areas considered by the NYPD to be among the most dangerous in the city. The two partners were told to do a check on the building, taking the elevator up to the top and then walking the length of each floor, in a procedure known as a vertical patrol.

But when they encountered a stairwell Landau described as “pitch black,” officer Liang removed his gun from his holster.

Earlier in the day, an NYPD firearms expert testified that officers are instructed to never have their fingers on the trigger unless they plan on firing their weapon.

Acting out their positioning during the shooting with an Assistant District Attorney next to the jury box, Landau demonstrated that Liang had the gun in his left hand, his flashlight in his right hand, and opened the stairwell door on the eighth floor with his shoulder.

In a surreal moment before Landau’s testimony, jurors were invited to shoot Liang’s gun, to test how much force it would take to pull the trigger.

“The shot just went off,” Landau testified. Liang immediately returned to the eighth floor hallway and it was there that the two had the argument, which Landau estimated lasted around four minutes.

Landau testified that he told Liang to “just call Sergeant Martinez [their supervising officer] and let him know you had an accidental discharge.” Landau says Liang resisted his advice.

“There was a back and forth over who was going to call it in. I told him to call and he told me to call,” Landau told the jury.

The bullet that Liang fired had ricocheted off a wall and struck Gurley on the seventh floor landing. Gurley was able to run down to the fifth floor before collapsing, and it was only when the officers went searching for the bullet that they became aware it had struck someone.

“I heard some kind of noise coming out from the floors below,” Landau testified. “I just hear some kind of noise. It was kind of like, grunting, crying, something along those lines. We ran down the stairs.”

When Liang encountered Gurley, Landau said Liang kneeled close to the body and said, “Oh my god, someone’s shot.”

Landau’s cross-examination will resume Thursday morning.