As the verdict was read, Liang dropped his head -- his hands around the back of his neck -- as one of his attorneys comforted him.
The rookie cop was fired after the highly unusual conviction of a police officer for the shooting death of a civilian.
Officer Shaun Landau, Liang's partner the night Akai Gurley, 28, was shot, was fired Friday, the New York Police Department announced. Landau, who was not charged with a crime, had been on modified assignment. He testified for the prosecution in the trial.
When the verdict was read, Gurley's partner, Kimberly Ballinger, dabbed tears and later pumped her fist in the air.
"He was a son. He was a brother," Brooklyn District Attorney Kenneth Thompson said after the verdict. "I told his mother, I'm sorry. There are no winners. This is a tragedy all over."
In a news release, Thompson added the decision was not a verdict against all officers of the NYPD, but one who ignored his official training.
The jury's verdict came after 17 hours of deliberations. Sentencing will be April 14.
The seven men and five women of the jury reached their decision on their second full day of deliberations after requesting white boards and the NYPD's firearm and tactics guide.
On Thursday evening, about an hour before the verdict, the jury asked Justice Danny Chun to read them the charges and legal definitions, the second time this week.
The case went to the jury Tuesday, with the panel deliberating for an hour.
Chun Wednesday denied a defense request for a mistrial, saying Liang's legal team fell "way, way short" in arguing that the prosecution in closing arguments implied the officer intentionally shot Gurley.
Jurors asked that the testimony of Liang and other witnesses be read back. And they asked the judge to reread the charges and replay a 911 call, which brought some of Gurley's relatives to tears.
The jury also asked to handle Liang's firearm, a request the judge allowed with the assistance of an officer.
During closing arguments, the officer's lawyer called the fatal shooting tragic, but not a crime, stressing that Liang followed procedures. Police determined that Gurley was "a total innocent."
"What happened here is a tragedy," defense attorney Rae Koshetz said. "It's a terrible tragedy, but it's not a crime."
Prosecutor Joe Alexis argued that Liang showed poor judgment, again and again, and that the shooting wasn't an accident beyond the officer's control. He asked jurors to hold Liang accountable.
The trial has garnered attention beyond New York because of the national controversy over allegations that police are too quick to use lethal force
, sometimes against unarmed people. Outrage over police shootings or excessive force has spurred protest movements in major cities such as Chicago, Baltimore and New York.
In the most well-known cases -- the fatal shootings of Michael Brown in Ferguson, Missouri
, and Walter Scott in North Charleston, South Carolina
, and the death of Freddie Gray while in police custody in Baltimore
-- the victims were unarmed black men.
'An accidental discharge'
Gurley was shot in the chest in Brooklyn and died at a hospital in November 2014.
The next day, police Commissioner William Bratton told reporters the 28-year-old was "a total innocent" who fell victim to "a very unfortunate tragedy ... involving an accidental discharge."
On Tuesday, the defense told jurors that Liang handled his firearm as trained, and that the video of the crime scene shows that having his weapon drawn in the darkness of the stairwell was the correct course of action.
Liang gave tearful testimony on the stand Monday, just before both sides rested in the case. He lost his composure when asked to recount what happened in the stairwell on that night
"I was panicking. I was in shock, in disbelief that someone was actually hit," he said.
The prosecutor has accused the rookie officer of recklessly shooting into a dark stairwell "for no reason."
"Then, instead of doing all that he could to help Akai Gurley, he wasted precious time arguing with his partner about calling for help," Assistant District Attorney Marc Fliedner told jurors last month
. "In fact, instead of calling for help, he just stood there and whined and moaned about how he would get fired."
Liang's lawyer has argued that the officer's gun accidentally discharged when he had it out while on patrol in the dangerous building. He was in shock, she said, and didn't know Gurley had been shot.
"He's shaken and terrified and totally, and I mean totally, unaware that a bullet has struck anything," Koshetz said.
When Liang and his partner went back into the stairwell to investigate, they discovered Gurley and his girlfriend on a stair landing below, Koshetz said.
"The evidence in this case will show that this was a million-to-one possibility. The bullet had traveled downward, hit the cinderblock wall on the side of the stairs and then ricocheted and hit Mr. Gurley a floor below and completely out of sight. And it hits him on his left side," she said. "It is a fatal wound, and you will hear that no amount of CPR would have saved his life."
Gurley's family: Not buying it
Gurley's family was less than sympathetic at a Monday afternoon news conference.
"Peter Liang says that it was an accidental death. Peter Liang, my son was no accident," said Sylvia Palmer, the victim's mother. "You murdered my son. I need justice for my son. I need a conviction of Peter Liang."
Stepfather Kenneth Palmer said the trial has taken its toll on the family.
"If you fire a gun and you know you're guilty, say 'I'm guilty' and that's it," he said. "Don't put any family through what we're going through."
The 2014 shooting death came amid strained relations between police and the community, just a few months after the death of Eric Garner
as police tried to arrest him on Staten Island. The chokehold death of Garner, an unarmed 43-year-old man, sparked street protests, a review of police procedures and calls for a federal civil rights investigation. A grand jury declined to prosecute the officer.
Liang was indicted
a year ago. He could face up to 15 years in prison.