Now Mr. O’Neill finds himself in a delicate position. He must strike a balance between supporting his rank-and-file officers and sending a message to New York’s elected leaders that the unnecessary death of an unarmed man in police custody will not go unpunished. He can choose to fire Officer Pantaleo and strip him of his pension, or take less drastic measures.

“For him, it’s going to be about the public symbolism and the morale of the Police Department,” said Richard Emery, the former chairman of the Civilian Complaint Review Board. “I don’t think there’s any doubt in his mind that there’s something wrong with what Officer Pantaleo did. But how do you punish him? It’s a very delicate decision.”

Chuck Wexler, the executive director of the Police Executive Research Forum in Washington, said commissioners in Mr. O’Neill’s position are in a no-win situation.

“They do know going in that some part of that constituency is going to be disappointed and some part is going to think it’s the right thing to do,” he said. “That’s what’s so tough about these decisions.”

The commissioner has given mixed signals about his intentions. He told the New York Daily News in 2017 that he had made up his mind. But when asked about the case at a City Council hearing on May 15 , he said he was waiting for the judge’s decision. “I won’t prejudge it,” he said.

Mr. O’Neill won praise recently from critics of the department for opening the notoriously opaque disciplinary process to an outside panel that recommended improvements. But when it comes to punishing officers who have been found by the administrative judge to abuse civilians, they say his touch has been as light as that of his predecessors. He has never fired an officer for using a chokehold.