Brooklyn prosecutors and a witness Monday described an NYPD rookie charged in a 2014 fatal housing-project shooting as cold and uncaring as the unarmed victim lay dying at his feet.

Officer Peter Liang seemed more interested in keeping his job than helping the man he had just shot, Akai Gurley, 28, Assistant District Attorney Marc Fliedner said at the start of Liang’s manslaughter trial.

“He didn’t even get down on the ground to touch him,” Fliedner said in his opening statement.

Liang, on the job for less than 18 months at the time of the Nov. 20, 2014, shooting, is accused of shooting Gurley once in the chest in a darkened stairway of the Louis H. Pink Houses in East New York.

NYPD officials said at the time that Liang’s weapon discharged accidentally as he and the victim crossed paths in the stairwell while the officer and his rookie partner patrolled the Linden Boulevard housing project.

Akai Gurley is seen in this Facebook photo. Photo Credit: Facebook

The officer also faces charges of second-degree assault, criminally negligent homicide, reckless endangerment and official misconduct.

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Liang has pleaded not guilty to the charges. Liang faces a maximum sentence of 5 to 15 years in prison if convicted.

One of his defense attorneys, Rae Downes Koshetz, told the jury the young officer was working overtime in one the city’s “most crime-ridden public housing developments” at the time of the shooting.

She said Liang “had his gun out because he was on his way up to the roof, which is the most dangerous place.”

Koshetz said Liang did not see or hear “a soul” as he opened the door to an eighth-floor landing, holding his gun and flashlight.

“Suddenly the gun goes off by itself,” Koshetz said.

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When Liang realized he had shot Gurley, “he was in shock and beside himself. He’s shaken and terrified. . . . He is in no shape to take care of himself or anyone else.”

Melissa Lopez, a resident of the complex who dialed 911 after the shooting, testified Monday that Liang and his partner “did nothing” while Gurley’s girlfriend pressed down on his bleeding chest with a towel as she attempted to revive him via mouth-to-mouth.

She said she called 911 and spoke with an emergency medical technician who gave CPR instructions, which she repeated to Gurley’s girlfriend.

Lopez testified that when “a million cops” showed up at the scene, she heard Liang tell his supervisor: “I shot him accidentally.”

Jurors heard a recording of the 911 call where Gurley’s girlfriend yell’s out: “He’s not breathing.’’

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Defense lawyer Robert Brown told Lopez her account Monday contradicted her grand jury testimony describing Liang as in “shock.”

Lopez stuck to her Monday testimony, telling Brown the rookie officer “looked stuck — just standing there doing nothing.”

Fliedner said Liang “in a split second with a flashlight in his hand burst into the stairwell and fired a shot towards the seventh floor.”

The bullet hit Gurley, Fliedner said, and “exploded through his chest.”

Outside the courtroom, Yiping Wu, 53, of Great Neck, joined half a dozen other supporters of Liang. Wu said he was present at the trial to show solidarity as an Asian-American.

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“We need to support our next, our new generation like Peter Liang, who is a good example of someone who wants to serve his community,” Wu said. “ . . . he worked in an environment where you can’t send a new guy out without supervision. He was scared just like any other human being.”