The Oakland police department will fire four officers and suspend seven others after a teenager revealed that some had traded police information for sexual favors.

The announcement Wednesday evening by Oakland Mayor Libby Schaaf caps a yearlong investigation that uncovered widespread wrongdoing in the department. The source of much of the information was a teen known by the pseudonym Celeste Guap, who claimed she’d had sexual encounters with 30 officers, sergeants and captains in multiple departments around the Bay Area.

“We care deeply about this community and its officers and believe that the outcomes in this case will root out misconduct, encourage a culture of transparency and continue the work of restoring trust,” Schaaf said in a statement.

Guap, now 19, said she was underage during some of the encounters and that officers knew it. She also claimed she received money and tips about undercover operations and prostitution raids from some officers in exchange for sex.

According to Schaaf, the four unidentified cops to be fired committed at least one of the following acts:

Attempted sexual assault

Engaging in lewd conduct in public

Assisting in the evading of arrest for the crime of prostitution

Accessing law enforcement database for personal gain

Being untruthful to investigators

Failing to report a violation of law, or rules by not reporting allegations of a minor having/had sexual contact with Oakland police officers

Bringing disrepute to the Oakland Police Department.

Some of the officers who will be disciplined did not have sexual contact with Guap, the investigation found. Those slated for suspension without pay had failed to report their fellow cops’ misconduct, misused police databases or dishonored the department, according to Schaaf. A 12th officer will undergo counseling for bringing disrepute to the force.

None of the officers is named because California state law prohibits identifying officers subjected to disciplinary action or even involved in personnel investigations.

Schaaf’s statement didn’t specify whether Guap said she was a victim of attempted sexual assault, and the mayor’s office didn’t immediately respond to HuffPost’s inquires.

While Oakland officials reviewed only the conduct of the department’s officers, the Alameda County district attorney may pursue criminal charges against them after completing a separate investigation. That should wrap up soon, Schaaf said. And although some of the Oakland cops may have already left the department, the findings will nonetheless go into their personnel files.

To prevent future abuse, Schaaf added, there will be better training for officers about victims of sexual exploitation, stricter controls on police databases and the creation of a policy for officers’ social media accounts.

An Oakland police spokeswoman declined to comment on Schaaf’s announcement.

The expansive probe into officers’ misconduct began last year, after the suicide of Oakland police officer Brendan O’Brien. He killed himself after Guap allegedly threatened to expose their relationship, TV station KGO reported. Guap says the two had sex when she was 17, but O’Brien denied that in a note, KGO said.

The fallout from the scandal created more instability in the upper ranks of a police force rocked by other controversies. During a tumultuous 9 days in June, three Oakland police chiefs departed in quick succession. The city administrator, a civilian, is temporarily at the helm while the city conducts a national search for a top cop to restore the department’s footing.

A federal monitor has overseen the Oakland police department for 13 years as part of the settlement of the so-called Riders scandal, in which four rogue cops beat and planted evidence on 119 plaintiffs. All but one of the victims was African-American.

Jim Chanin, one of the attorneys who brought the Riders case, said the department did a poor job investigating Guap’s allegations before the upheaval that pushed out three police chiefs. Since then, the investigation became more aggressive.

“What’s important is not that they never happen but that they’re stomped on effectively by the command staff and internal affairs. That did not happen here,” Chanin said.