Police in Vallejo, Calif., fire officer in 2020 shooting death of Sean Monterrosa

A police detective in the San Francisco Bay Area city of Vallejo was fired after an independent investigation concluded that his use of deadly force in the shooting of a 22-year-old man in 2020 "was not objectively reasonable" — a rare move by a department that has come under review for its high rate of fatal shootings by officers.

The Vallejo Police Department, which commissioned the investigative report, did not name the officer in a news release Monday, but an attorney with the family of the man who died, Sean Monterrosa, identified him as Jarrett Tonn, a detective with the department for more than six years.

The department has not publicly named Tonn nor the other officers who responded to a report of looting at a Walgreens after midnight on June 2, 2020. The incident came amid widespread protests in the wake of the killing of George Floyd by police in Minneapolis.

Vallejo police officials aren't identifying the fired officer because a court order in a related lawsuit brought by the union, the Vallejo Police Officers' Association, prevents them from doing so.

The department and the city also declined to comment further, but said it would make a redacted copy of the "notice of discipline" publicly available.

Neither Tonn nor his attorney could immediately be reached for comment, and it was unclear whether he planned to challenge his firing in arbitration.

He was placed on leave in the aftermath of the shooting of Monterrosa, who was from San Francisco. At the time, authorities said, an officer arriving at the scene was sitting in the back of an unmarked police truck when he fired five times through a windshield, fatally hitting Monterrosa, who the officer believed had a gun and was kneeling "in preparation to shoot."

Monterrosa had stopped and was crouched down in a half-kneeling position facing the officers, authorities said, and investigators later retrieved a hammer from his sweatshirt pocket.

A month after the shooting, police released officers' body camera footage. Three officers in the truck had activated their cameras, but none of the videos showed Monterrosa prior to Tonn firing his weapon through the front windshield. The vehicle itself did not have a camera.

In a notice to Tonn on Dec. 1, 2021 warning that he was facing termination, Vallejo Police Chief Shawny Williams noted that while the officer felt compelled to use his Colt M4 Commando rifle, none of the other officers at the scene had even unholstered their weapons.

"Your generalized concern that people were engaged in criminal activity, i.e. looting, did not give you a reasonable basis to believe that Mr. Monterrosa, in particular, posed a threat of death or serious bodily injury to you or anyone else," Williams wrote. In addition, the police chief said that Tonn "failed to timely active your body worn camera," which violates department protocol, and his actions "undermine public confidence" in the department.

But at a hearing in April, an outside consultant reviewing the case recommended that he not be fired.

The Vallejo Police Officers' Association said Tuesday it was "disappointed" that Williams went against that guidance and "unilaterally decided to terminate our member."

"We are confident this egregious political move will be overturned in arbitration," the union said in a statement.

The firing of a police officer in Vallejo for actions while on duty is rare and comes as the California Department of Justice is conducting an "expansive review" of the city's police department after the community demanded accountability over fatal shootings by officers, with the majority of those killed Black men and other men of color, records show. Monterrosa was Latino.

Vallejo last fired an officer in October 2020 in connection with the death of Willie McCoy, a local rapper who was shot by officers 55 times in 3.5 seconds. That officer, however, was not fired over his use of deadly force but because Williams said he had endangered the lives of other police officers, neglected basic firearm safety and demonstrated "unsatisfactory work performance."

The state Department of Justice's investigation into the death of Monterrosa is ongoing. House Speaker Nancy Pelosi had called for the FBI to investigate as well.

In the weeks after the shooting, the city confirmed that the bullet-riddled windshield from the police truck from which the officer fired had been destroyed. A police lieutenant was placed on administrative leave in connection with the windshield's destruction.

Monterrosa's family said in a social media post Monday that while they believe Tonn should have been fired immediately, they were "grateful for this administrative step."

"After two years we continue to demand that the California DOJ under the leadership of [state Attorney General] Rob Bonta take immediate action to prosecute and hold the responsible Vallejo officers accountable for their crimes," said the family, which has a pending wrongful death lawsuit against the city and Tonn.

The city has denied the allegations in the suit.

Melissa Nold, an attorney who is working with Monterrosa's family on advocacy issues, has said that reviewing the windshield was necessary to accurately recreate the scene and help determine the trajectory of the bullets, since bodycam video does not show Monterrosa until he was already lying on the ground.

"Tonn's termination is a pivotal step towards reform and accountability," Nold said Tuesday. "Real leadership requires difficult and sometimes unpopular decisions, but rules and laws must be enforced."

This article was originally published on NBCNews.com