OAKLAND, Calif. (CN) – A veteran police sergeant has sued Oakland, California, saying the police department covered up for a fellow officer who allegedly killed his own wife, and failed to investigate allegations that police were sexually exploiting a teenage girl after the officer revealed it in a suicide note.

In the whistleblower lawsuit in Alameda County Court, Sgt. James Gantt says he was harassed, denied promotion and placed on administrative leave after he identified Officer Brendan O’Brien as a suspect in the 2014 death of O’Brien’s wife, Irma Huerta Lopez.

Gantt, a 28-year veteran of the department and a decorated homicide investigator, says his superiors called the death a suicide and cleared O’Brien of wrongdoing despite evidence that he had killed Huerta Lopez in their Oakland Hills home, then retaliated against him to “silence” him so he wouldn’t reveal the cover-up.

The Alameda County District Attorney’s Office also ruled Huerta Lopez’s death a suicide, but Gantt says that evidence at the scene pointed to murder, and to O’Brien as her killer.

Two bullets had been fired, which Gantt called “unusual” for a suicide, and one of the bullet shells landed at Huerta Lopez’s right foot rather than at her side. Moreover, the bullet hole in the wall of the room where Huerta Lopez died indicated that the bullet was fired from the door of the room, not by Huerta Lopez from the bed where her body was found, according to the complaint.

Nor did Gantt believe O’Brien’s alibi that he was out buying cigarettes when Huerta Lopez killed herself — because didn’t smoke. “In addition, O’Brien stated that he had walked barefoot for a mile to the store,” Gantt says in the complaint.

It continues: “Gantt learned that O’Brien had left his gun and badge at the house, even though officers, especially white male officers in East Oakland, rarely leave their guns and badges behind when they go out onto the streets.”

Gantt’s attorney Dan Siegel with the Oakland civil rights firm Siegel & Yee said in an interview that Gantt ran into the Blue Wall when he refused to cover for O’Brien.

“He was taking an approach to this investigation that was contrary to the very protective internal environment the Oakland Police Department and many police departments have, so he clearly angered people in the Homicide Division who really treated him terribly after this investigation,” Siegel said.

O’Brien killed himself a year later. He revealed in a suicide note that he and several other Oakland police officers had been sexually exploiting an underage girl who previously went by the name Celeste Guap.

Guap, the daughter of an Oakland police dispatcher, claimed to have had sex with dozens of officers from seven law enforcement agencies around the Bay Area. Criminal charges were filed in September last year against six officers, including five from Oakland, accusing them of having oral sex with Guap while she was a minor, prostituting her and accessing criminal databases on her behalf without permission.

In his complaint, Gantt says city officials targeted him for criticism as the sexual misconduct scandal unfolded to distract from their failure to investigate the allegations, which were leaked to the public in June 2016.

That month, Schaff and City Administrator Sabrina Landreth, also a defendant in Gantt’s lawsuit, held a news conference accusing Gantt of allowing a woman to transcribe confidential audio recordings that were used as evidence in a 2013 homicide investigation. The District Attorney’s Office cleared Gantt of criminal wrongdoing

Then Schaff announced that two officers were being investigated for sending racist text messages to other officers, on the same day that she announced that Police Chief Paul Figueroa had resigned as acting chief after two days on the job.

While the city did not identify the officers it was investigating for the texts, media reports widely cited Gantt as one of them. Gantt says in his complaint that he was threatened with suspension over the texts.

He has been on paid administrative leave since an April 2016 altercation with his wife at their home in Hayward.

Siegel said on Thursday that Gantt was a natural target for city officials who needed to shift blame for the scandal after he drew their ire during the investigation of O’Brien.

“Fast-forward to next year and there is this series of leaks coming out of OPD, which is really getting Mayor Schaff’s goat,” Siegel said of the leaks that revealed the scandal. “Likewise, there were upset people in the community who felt the department was involved in this bad behavior, there hadn’t been an effort to uncover it and deal with the sex scandal, and I think they were looking for scapegoats.”

Schaff’s spokeswoman Erica Terry Derryck declined to comment on the lawsuit, and directed inquiries to the City Attorney’s Office. City Attorney spokesman Alex Katz also declined to comment, saying the city had not yet reviewed the allegations.

Though Gantt has won multiple awards for his work, including a national police officer of the year award in 2001, he was fired on allegations of hindering a 2004 rape investigation that involved his friend. He was reinstated.

It’s just the latest in a continuing series of scandals for Oakland police.

U.S. District Judge Thelton Henderson has twice indicated that he is not satisfied with how the city investigated the sex abuse allegations. Henderson wrote in a Feb. 14 order that he has appointed an independent attorney to review the city’s investigation, and granted him access to privileged correspondence from the Oakland City Attorney’s Office to facilitate the inquiry.

That order came nearly a year after Henderson turned over the investigation to a federal monitor, after revelations that the police department knew about the allegations but had failed to properly investigate them.

“This case raises most serious concerns that may well impact defendants’ ability to demonstrate their commitment to accountability and sustainability,” Henderson wrote in the March 2016 order.

“At the end of the day, a court is going to decide who is telling the truth here,” attorney Siegel said in the interview. “Whether the accusations against Officer Gantt are valid, meritorious accusations … or if in fact he is being subjected to retaliation because he’s done things that have angered other people in the police department and contributed to the embarrassment of city officials.”

Gantt seeks reinstatement, lost wages and benefits and punitive damages for civil rights violations, retaliation, emotional distress and pain and suffering.