On the vast lawn of the plaza near the courthouse in Brooklyn where Peter Liang, a former New York City police officer, was convicted in the fatal shooting of an unarmed black man just over a week ago, a crowd of several thousand people gathered on Saturday.

They chanted, “No scapegoat! No scapegoat!” and carried signs bearing the same message. Some said they had never had a reason to protest before, while others said they had taken the day off from work or had come by train and bus from across the city — or as far as New Jersey and Connecticut — to take part in the demonstration at Cadman Plaza Park to show their support for Officer Liang.

Prosecutors had described Officer Liang’s behavior as reckless when he fired his gun inside a public housing complex, and argued that after the man, Akai Gurley, had been shot, the officer seemed more concerned about his career than in helping Mr. Gurley, who was 28.

Yet Officer Liang’s conviction has gripped many in the city’s Chinese-American community, who believe that he had been targeted for prosecution because of his race. They followed the case closely and have been denouncing the jury’s verdict, arguing that Officer Liang, 28, was a victim himself.