SAN FRANCISCO (AP) — The Oakland Police Department lost its seventh head of police in as many years Wednesday over the alleged cover-up of an officer’s misconduct in a scandal that threatens to extend two decades of federal oversight — the longest of any police department in the country.

Democratic Mayor Sheng Thao said at a news conference she was firing Police Chief LeRonne Armstrong after a probe concluded the chief and the department failed to properly investigate and discipline a sergeant who was involved in a hit-and-run with his patrol car and, in a separate incident, fired his service weapon inside an elevator at police headquarters.

Thao, who took office in January, said she wants to be confident the police chief in the city of 400,000 people will be effective “in making improvements that can be recognized by the federal monitor, the federal court and the people of Oakland.”

“I am no longer confident that Chief Armstrong can do the work needed to achieve the vision so, today, I have decided to separate Chief LeRonne Armstrong from the city without cause,” she said.

Thao placed Armstrong on paid administrative leave last month to review investigations by the department’s federal monitor that found the police chief responsible for gross dereliction of duty.

The probes by the law firm of Clarence Dyer and Cohen concluded Armstrong failed to investigate and discipline Sgt. Michael Chung after he was involved in a hit-and-run with a parked car in 2021 at his apartment building in San Francisco, according to a report first obtained by KTVU-TV and made public by Oaklandside, a local news site.

The Oakland Police Department made national news in 2000 after a rookie officer came forward to report abuse of power by a group of officers known as the Oakland “Riders.” The four officers were charged with making false arrests, planting evidence, using excessive force, falsifying police reports and assaulting people in west Oakland, a predominantly Black area. Three of the officers were acquitted after two separate juries deadlocked on most of the charges. The fourth officer is a fugitive and is believed to have fled the country.

The case resulted in the department coming under federal oversight in 2003 and being required to enact 52 reform measures and report its progress to an outside monitor and a federal judge.

Armstrong, a native of Oakland, was appointed in 2021 with promises of enacting all the reforms within a year.

He said he was deeply disappointed in Thao’s decision and that once all the facts are evaluated, it will be clear he committed no misconduct and his termination was “wrong, unjustified, and unfair.”

“After the relevant facts are fully evaluated by weighing evidence instead of pulling soundbites from strategically leaked, inaccurate reports, it will be clear I was a loyal and effective reformer of the Oakland Police Department,” he said in a statement.

In its report, the law firm said a police captain in the department’s Internal Affairs Division downplayed the hit-and-run incident and coached the investigating officer to draft a report that allowed Chung to escape discipline.

The following year, Chung fired his service weapon inside an elevator at police headquarters, got rid of evidence and did not inform his supervisors until a week later. He has been on paid administrative leave since then.

“Sgt. Chung escaped serious discipline and was left to commit even more egregious conduct — discharging his firearm in an elevator — which he also failed to report and tried to cover up,” the investigators said.

The law firm report concluded Armstrong failed to hold his subordinate officers accountable.

Federal Judge William Orrick last year put the agency on a one-year probationary period that was set to end by June and finally free it from federal oversight, saying the department had achieved “substantial compliance.” But last month, he made public a portion of the law firm reports, prompting the mayor to place Armstrong on paid leave.

“The report … demonstrates that the significant cultural problems within the department remain unaddressed,” he said during a virtual hearing in January.

Orrick ordered the city to present a plan by April 4 on how it plans to come into compliance.

Armstrong, the 13th person to head the embattled police department in 20 years, received the backing of some of the city’s Black leaders, including John Burris, one of two attorneys who in 2000 filed the lawsuit against the police department on behalf of 119 plaintiffs.

Burris said he was disappointed that Thao based her decision on what he considers to be “not very strong evidence of wrongdoing on the part of Mr. Armstrong.”

Burris, who has been meeting on a regular basis with the police department and federal monitor for the last 20 years, said the police department has made great strides and positive changes on how it deals with the community, which largely supported Armstrong.

“We don’t have the beating that we used to have. We don’t have people being stopped because of their race at the same level we had before. We don’t have the shooting and the use of deadly force that we had before. We don’t have the mistreatment of the mentally impaired in the same way we did,” Burris said.

“But this is a (police) culture question and the disappointing part is it hasn’t changed,” he added.