NEW YORK — A rookie police officer who shot an unarmed man dead in a darkened public housing stairwell was convicted Thursday of manslaughter in a case closely watched by advocates for police accountability.

The courtroom audience gasped and Officer Peter Liang, who had broken into tears as he testified about the 2014 shooting of Akai Gurley, buried his head in his hands as the verdict came after 17 hours of jury deliberations. Liang is the first New York City police officer convicted in an on-duty death since 2005.

The manslaughter charge, a felony, carries up to 15 years in prison, though no requirement for any prison time. Liang was dismissed from the New York Police Department right after the verdict. His sentencing is April 14.

But an uncertainty remains: Brooklyn state Supreme Court Justice Danny Chun has yet to rule on Liang’s lawyers’ request to dismiss the charges. Liang also was convicted of official misconduct, a misdemeanor.

Brooklyn District Attorney Kenneth Thompson said “justice was done” for Gurley.

“He was an innocent man who was killed by a police officer who violated his training,” said Thompson, whose mother was a police officer.

But Liang’s lawyers said they struggled to understand how the jury could find him guilty in a shooting he said happened accidentally in a pitch-dark stairway.

“If that’s not a time to pull out your gun, I don’t know when is,” said defense lawyer Robert Brown. He said Liang would appeal.

Liang, who remains free on bail, left the courthouse without comment.

The shooting happened in a year of debate nationwide about police killings of black men. Activists have looked to Liang’s trial as a counterweight to cases in which grand juries have declined to indict officers, including the cases of Michael Brown in Missouri and Eric Garner in New York. Like Gurley, Brown and Garner were black and unarmed. Liang is Chinese-American.

Thompson cautioned that Liang’s case shouldn’t be commingled with others. But relatives of other New Yorkers killed in police encounters had joined Gurley’s family outside court during the trial to call for police accountability.

“I just want to say thank you, thank you, thank you to everyone,” Gurley’s mother, Sylvia Palmer, said after the officer’s conviction.

Meanwhile, Liang’s supporters have said he was scapegoated for past injustices.

And the head of Liang’s union, Patrolmen’s Benevolent Association President Patrick Lynch, said the verdict “will have a chilling effect on police officers across the city because it criminalizes a tragic accident.”