"I am here to run a police department," she said, "not a frat house."

Schaaf's city, Oakland, California, has cycled through three police chiefs in less than two weeks as the department faces a rapidly spiraling controversy that shows no signs of slowing.

The shakeup started with a sex scandal. And as she stepped to the podium Friday, Schaaf told reporters she had more bad news to share.

The latest twist: an investigation into racist text messages.

That, Schaaf said, made her decide to hold off on appointing another interim top cop.

"I feel that this is an appropriate time to place civilian oversight over this police department," she said, "and to send a very clear message about how serious we are, of not tolerating misconduct, unethical behavior, and to root out what is clearly a toxic, macho culture."

Since June 9, three police chiefs have been fired or resigned.

The police union didn't immediately respond to a request for comment. And authorities have been tight-lipped about the changes at the helm. Schaaf told reporters she's constrained by California laws that stop her from speaking out on personnel issues.

"I have not been able to share the full story, because I may not under state law," the mayor said.

Allegation: Sex scandal involved a number of officers

It all started last fall with an officer's suicide. Officials say an investigation into his death uncovered disturbing allegations.

Oakland police sexual misconduct probe sparked by suicide. https://t.co/TCpY7AdYxq pic.twitter.com/ZkWPwUyDCY — KRON 4 News (@kron4news) May 14, 2016

Within months, an 18-year-old alleged she had sex with him, as well as with a number of other officers from the Oakland Police Department and officers from nearby jurisdictions.

The 18-year-old, who describes herself as a former prostitute and goes by the pseudonym Celeste Guap, told CNN's Nick Valencia on Sunday that she has a message for people following the controversial case.

"There's people saying that I wanted this to happen, that I screwed over all these cops on purpose, that it was me who put it out there and stuff," she said. "As long as people know that I didn't want this to happen."

It all started, she said, when she was 17 years old and became romantically involved with an officer who saved her from her pimp. That officer, she said, introduced her to other cops who became customers.

Details are still emerging about the case, and no charges have been filed.

A group of demonstrators protested outside police headquarters in Oakland on Friday. Two climbed flagpoles to hang a banner that read: "OPD guilty of: human trafficking and statutory rape."

The mayor has slammed the situation, while providing few details.

"We continue to be disgusted and outraged by the idea that anyone could abuse an underage victim of sexual exploitation -- particularly those who have sworn to uphold the law and protect our communities," Schaaf said last week. "We are sickened to think anyone could even know of such abuse and not bring that information forward."

Allegation: Officers sent racist text messages

When Schaaf announced the investigation into racist text messages, she said she couldn't specify how many officers sent them, what they said or when the messages were sent.

"We do think it's relevant to share that the text messages were sent by African-American officers, but they are wholly inappropriate and not acceptable from anyone who wears the badge of the Oakland Police Department," she said. "This investigation should be concluded within a matter of days, perhaps a week or two, and I will not share any additional information, because I do not want to compromise our ability to seek the maximum punishment available for these alleged acts."

One officer already has been placed on leave in connection with the investigation, she said.

We are hell-bent on rooting out this disgusting culture and holding those accountable responsible for their misdeeds. Oakland Mayor Libby Schaaf

The mayor said the number of officers involved in the racist text messages scandal was not as widespread as the sex scandal. The two scandals aren't related, she said.

She laughed when a reporter asked if any other police officials would be let go.

"I'm hoping to not have to fire anyone else anytime soon, but we will continue to take this matter extremely seriously," she said.

Feds already monitor department

This isn't the first time police in Oakland have come under scrutiny. The department has been under federal monitoring since 2003 as part of a settlement in a police misconduct case.

A visibly disheartened Schaaf said Friday that the police department has made progress and that it was a shame many good officers were being tainted by the scandals.

"The good men and women of the Oakland Police Department do not deserve to have their good work, their progress in making this city safer and implementing progressive reforms, marred by this scandal," she said. "I want to assure the citizens of Oakland that we are hell-bent on rooting out this disgusting culture and holding those accountable responsible for their misdeeds."

Without a police chief at the helm, Oakland City Administrator Sabrina Landreth will be responsible for administrative and personnel decisions, the mayor said. Oakland police commanders will make operations decisions.

But more oversight might be necessary, Oakland City Councilman Noel Gallo told CNN affiliate KRON

"We may have to go to complete federal oversight of our police department," he said.

City Council President Lynette Gibson McElhaney told CNN affiliate KGO that she's trying to keep the mounting allegations in perspective.

"I still believe the vast majority of our officers serve with integrity and honor in a very difficult climate," she said. "For me, it's been difficult to think, how do we recruit at a time like this?"