“Do your job,” she said. “Come forward and show yourself as the mayor you were elected to be.” As she spoke, Mr. de Blasio, who won election largely because of support from black New Yorkers while promising to hold the police accountable, was at Gracie Mansion, miles away.

City law seems to preclude the city from firing Officer Pantaleo until the conclusion of the hearing.

Given the facts of the case, it’s hard to see his continued employment by the Police Department as anything but an insult to the people of New York.

Mr. Garner, who was unarmed and supposedly selling loose cigarettes, which is illegal, died because Officer Pantaleo used a chokehold. The Police Department banned the use of chokeholds in 1993 amid a rise in deaths linked to the maneuver.

In searing testimony at the departmental trial this year, the medical examiner said the chokehold triggered an asthma attack that led to Mr. Garner’s death, which he ruled a homicide.

A police internal affairs investigator also testified that he recommended disciplinary charges against Officer Pantaleo in 2015. None came until last year.

Beyond any violation of departmental rules, Officer Pantaleo’s actions violated good sense and demonstrated the kind of overly aggressive policing that has led to many controversial deaths. He chose to escalate an encounter, involving several officers, with an unarmed man over a minor violation, then used a dangerous and banned maneuver. Video of the episode, viewed by millions, shows the officer with his arm across Mr. Garner’s throat.