NEW YORK (CBSNewYork/AP) — Testimony is continuing Tuesday in the trial of a rookie NYPD officer charged in the shooting death of a Brooklyn man.

Officer Peter Liang is accused of firing his gun in a darkened stairwell at the Pink Houses in East New York back in 2014, killing Akai Gurley.

Police Officer Salvatore Tramontana, who was the first to respond to the radio call reporting a man shot in a stairwell, testified Tuesday that he rushed into the building unaware that a police officer had shot an innocent man, WCBS 880’s Irene Cornell reported.

Tramontana said he immediately stepped in to do CPR, taking over for Gurley’s girlfriend, Melissa Butler, who he described as crying hysterically.

The officer said he kept performing CPR and yelling at the victim, trying to rouse him, even though he had no pulse.

On Monday, jurors heard the dramatic 911 call where Butler can be heard in the background trying to administer CPR.

“He’s not breathing!” Butler yelled as the caller stood nearby and relayed a medic’s phone instructions for CPR.

The recording also captured a brief exchange between the caller — a resident who heard the shot — and Liang and his partner. The uniformed officers appeared while Butler, her hands covered in blood, was frantically trying to save Gurley’s life. But they never offered any assistance as they descended the stairwell, Melissa Lopez told the jury.

Liang “didn’t do nothing,” Lopez said.

Prosecutors sought to use the recording and Lopez’s testimony to show that, along with recklessly firing his weapon, he callously ignored his duty to aid his victim.

“A police officer, this police officer, shot an innocent person and he never even knelt down and try to fix what he’d done,” prosecutor Marc Fliedner said in opening statements Monday.

The defense claims Liang, because his weapon accidentally discharged, didn’t commit a crime. The officer has pleaded not guilty to second-degree manslaughter, criminally negligent homicide and other charges.

“Peter Liang had no intent to hurt anybody,” said defense lawyer Rae Koshetz.

At the time of the shooting, Liang, an officer for 18 months, and his partner were patrolling the Brooklyn housing project amid reports of a spike in violent crime. The officer had his gun drawn as he entered the stairwell on the eighth floor because he was headed to the roof, “the most dangerous place of a dangerous place,” his lawyer said.

The 28-year-old Gurley and Butler had already entered the door into the seventh-floor landing to head down to the exit. Liang, his gun in his left hand and using a flashlight in his right because the lights were burned out, fired a shot that ricocheted and hit Gurley, who made it down two flights of stairs before collapsing.

Koshetz said Liang initially had no idea the bullet had struck anyone. Once he learned, “he was in a state of shock and was hyperventilating,” she said.

But prosecutors said after the gun went off, rather than check to see if someone was hurt, Liang repeatedly told his partner it was an accident, argued over which one should report it and fretted about what it would mean for him.

Liang “stood there whining and moaning about how he could get fired,” Fliedner said.

Under cross-examination by the defense Tuesday, Tramontana confirmed that the Pink Houses have a reputation of being one of the most dangerous projects in the city.

Prosecutors are expected to call Butler and Liang’s partner as their key witnesses. Liang also is expected to testify in his own defense.

Gurley’s family has brought a wrongful-death lawsuit on behalf of his estate and his young daughter.

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