OAKLAND — The Oakland police scandal reached a new low Friday night as the department lost its third chief in a week amid accusations that several African-American commanders had sent racist text messages to each other and that a sergeant had his girlfriend ghostwrite his homicide report in a high-profile 2013 murder case.

“I’m here to run a police force, not a frat house,” a visibly angry Mayor Libby Schaaf said Friday evening, referring to the department’s growing list of scandals, which until this week had centered on allegations that multiple officers had sex with the teenage daughter of a police dispatcher.

Sources say that Sgt. Mike Gantt came forward about the alleged 2-year-old racist text messages after learning that he was under investigation himself.

The saga appeared to prove too much for Acting Chief Paul Figueroa, who voluntarily took a leave of absence and demotion to captain after struggling with the stress of a job he held for only two days, sources said.

After considering tapping a new acting chief — who would have been the department’s fourth in eight days — Schaaf instead placed City Administrator Sabrina Landreth in charge of the department and pledged to root out a “toxic, macho culture” that she also described as “disgusting.”

The mayor called for civilian oversight of the police department.

Multiple sources said police commanders — lieutenants and officers both white and African-American, and some in the homicide unit — frequently texted each other, and at least two of those messages were racially charged. One of those messages depicted a picture of Klansmen suggesting that they did not need to harm black people because black people were killing each other.

Lt. Tony Jones has been placed on leave as part of the ongoing investigation, multiple sources said.

Jones and Gantt, who are both African-American, had a falling out, which led to Gantt going to investigators with text messages dating back to at least 2014, sources said.

Gantt is under investigation for mishandling a homicide case, apparently leaving evidence at the home of a girlfriend who would also do his investigative paperwork, according to sources. The veteran homicide detective who handled several high-profile cases is also on leave, sources said.

The evidence was part of Gantt’s investigation into the shooting death of 66-year-old Judy Salamon. Salamon was killed in July 2013 after using her cellphone to take a video of her suspected killers committing a crime in her Maxwell Park neighborhood. Stephon Lee, 22, and Mario Floyd, 21, have been charged with homicide in her death and are awaiting trial.

The case and numerous others investigated by Gantt could be compromised if he made a habit of not authoring his own homicide reports.

The city now has no police chief after cycling through three chiefs in eight days. Figueroa replaced Ben Fairow, whom Schaaf fired Wednesday after he apparently admitted to having an extramarital affair while working in the department more than a decade ago. Fairow, who was on loan from BART, where he serves as a deputy chief, was the city’s top cop for five days, having replaced now ex-Chief Sean Whent.

Whent was pushed out as chief June 16 because of the department’s sexual misconduct scandal, according to sources. Figueroa was the fifth chief in Oakland since 2013.

“We’re left with an administrator, and she doesn’t know anything about policing,” Councilman Noel Gallo said. “It all comes down to lack of experience and failed leadership, We went from worse to worse.”

“The department is spiraling out of control, and we need to stop it,” Councilwoman Desley Brooks said. “The mayor needs to demonstrate some leadership. I’m extremely disappointed. It’s embarrassing for the members of the department as well as the city.”

Meanwhile, police and the Alameda County District Attorney’s Office continue to investigate claims that officers were sexually involved with a police dispatcher’s daughter who worked in the sex trade and was underage during some of her contact with officers.

When asked who might be next to go, Schaaf said: “I’m hoping to not have to fire anyone else anytime soon, but we will continue to take this matter extremely seriously.”

Staff writer Matthias Gafni contributed to this report. Contact David DeBolt at 510-208-6453. Follow him at Twitter.com/daviddebolt.