Liang was sentenced to 800 hours of community service and five years' probation Tuesday after Judge Danny Chun reduced his manslaughter conviction to criminally negligent homicide in the shooting death of Gurley, 28, who was not armed.
But Chun said that for manslaughter to stand, the prosecution had to prove that Liang not only "created a substantial and unjustifiable risk that a death would occur" but also that the the officer "was aware of and consciously disregarded that risk."
"There is no evidence either direct or circumstantial that the defendant was aware of Akai Gurley's presence and still disregarded any risk by firing the weapon," Chun said. "The evidence showed that it was a quick reaction to perhaps a sound, which in my opinion only amounts to failing to perceive a unjustifiable risk."
The prosecution said it will appeal the judge's decision to reduce the verdict.
"My office vigorously prosecuted Peter Liang for manslaughter because the evidence established that his conduct was criminal and the rule of law demanded that he be held accountable for his actions in taking Akai Gurley's life," Brooklyn District Attorney Ken Thompson said in a statement.
"The jury, the voice of the Brooklyn community, agreed and returned the verdict of guilty against Mr. Liang, who is now a convicted felon, forfeited his career as a police officer and must now always live with the fact that he recklessly caused Mr. Gurley's death."
Liang, who was immediately fired after his conviction, on Tuesday apologized to Gurley's family.
"Growing up my parents thought it was a foolish dream that I wanted to become a police officer," he told the court. "When I graduated from the academy it was a dream come true."
He added, "Judge, my life is forever changed. I hope I have a chance to improve."
Gurley's domestic partner, Kim Ballinger, told the court that Liang's reckless actions changed many lives. She described Gurley as a "lovely father" and said their young daughter asks why a police officer killed her father.
"An innocent man was shot and killed due to the reckless actions of a police officer and then, after the shooting, a police officer did nothing to help him as Akai lay bleeding to death on a cold stairway," she said.
Thompson had written the judge with a recommendation of five years of probation, including six months of home confinement with electronic monitoring and 500 hours of community service. Liang faced up to 15 years in prison.
"Mr. Liang has no prior criminal history and poses no future threat to public safety," Thompson said in a statement last month. "Because his incarceration is not necessary to protect the public, and due to the unique circumstances of this case, a prison sentence is not warranted."
Liang, with 18 months on the job, was on patrol in the dark stairwell of a Brooklyn housing project in November 2014 when he fired his gun. The bullet ricocheted off a wall and struck Gurley in the chest. Gurley died at a hospital.
Liang's lawyers argued that the officer's gun accidentally discharged when he had it out while on patrol in the dangerous building. He was in shock, and didn't know Gurley had been shot, the lawyers said.
Defense lawyers called the shooting a tragedy, not a crime. Prosecutors argued that Liang was reckless and was more concerned about his story than helping Gurley.
Liang gave tearful testimony on the stand during the trial. When asked to recount what happened in the stairwell on that night, he said he lost his composure.
"I was panicking. I was in shock, in disbelief that someone was actually hit," he said.
Liang had a brief meeting last month with Ballinger at Thompson's Brooklyn offices, according to attorneys for Liang and Ballinger, who were present.
"He said how sorry he was that she had lost a loved one," attorney Paul Shechtman said of Liang. "He said how difficult a year it had been for him and could only imagine how difficult it was for her."
Ballinger did not accept his apology, according to her attorney, Scott Rynecki.
"She looked him right in the eye and said, 'I just want to let you know that your actions that night have left my daughter without a father, have left me without a partner,' " Rynecki recalled.
Gurley's death "turned her life upside-down," Ballinger told the ex-cop.