OAKLAND — A longtime Oakland police sergeant is suing the city on allegations that he was harassed and retaliated against for pursuing a fellow officer as a suspect in a homicide investigation and for speaking out against racism within the department.

The lawsuit filed by James Michael “Mike” Gantt in Alameda County Superior Court last week seeks general and punitive damages and calls for a jury trial. The city of Oakland did not immediately return a request for comment Monday. Gantt declined to comment.

Gantt,, who is black, is a highly decorated investigator employed by the department since 1998. He filed a claim against the city in November that revealed the same allegations of racism and retaliation for pointing the department to evidence that a fellow officer killed his wife in 2014. Gantt said he was also retaliated against for reporting racist texts, including Ku Klux Klan images, that he had received from other officers in 2014.

Gantt alleges he started being harassed by members of the department in 2014 after he was removed from the investigation of the fatal shooting of Irma Huerta Lopez, the wife of Oakland police Officer Brendan O’Brien. The department ruled her death a suicide, a classification later reaffirmed by the Alameda County District Attorney’s Office, but Gantt believes O’Brien may have killed her. The woman’s family also believes O’Brien was responsible.

O’Brien killed himself in September 2015, leaving behind a suicide note in which he named some officers who had been sexually involved with a teenage daughter of a police dispatcher who previously used the name Celeste Guap. The exploited young woman claimed to have had sexual relations with about 30 Bay Area officers, and seven current and former Oakland officers were later charged with crimes during the ensuing scandal. In claims that seek millions of dollars from Oakland, San Francisco, Richmond and other local municipalities, the woman alleges she was sex-trafficked as a minor.

Gantt’s lawsuit outlines reasons he suspected O’Brien had killed his wife, despite O’Brien’s claims that she shot herself while he was out buying cigarettes after a fight: O’Brien didn’t smoke and claimed he walked to a store a mile away while barefoot. He admitted that he cheated on his wife and they had been fighting about his infidelity. There were two shots fired, which is unusual in a suicide. The placement of the bullets and the bullet shells was inconsistent with the suicide narrative. And Huerta Lopez had removed her wedding ring and had packed a bag, indicating she had planned to leave, the lawsuit says.

Gantt alleges that when he pointed out the evidence to Inspector Caesar Basa, Basa said “don’t be so closed-minded” and told him it looked like a suicide. As soon as he started questioning O’Brien as a suspect, Gantt said he was told he lacked compassion and was pulled from the investigation by then-Lt. John Lois and replaced by an inexperienced homicide investigator.

Gantt claims that Basa and Lois began a “campaign of harassment” after that, and thereafter he was routinely denied assignments and at least one promotion.

Gantt further alleges that Oakland police leadership ignored the allegations of sexual misconduct in O’Brien’s suicide note until court-appointed monitor Robert Warshaw learned of the allegations and demanded an investigation in February 2016.

The sergeant also said top OPD officials, including former Chief Sean Whent, knew about the sex scandal but the department didn’t investigate what they knew or how the case was handled.

The lawsuit names the city of Oakland, Mayor Libby Schaaf, City Administrator Sabrina Landreth, Deputy Chief John Lois and John Does 1-50 as defendants.

Gantt was placed on administrative leave in April, when he was involved in a domestic incident with his wife at their home. The incident did not involve injuries to either party, and he and his wife declined to press charges against each other. Gantt’s lawsuit alleges the department prolonged his leave to “discredit and silence him” and that the city has pursued numerous baseless claims against him in the interim. He returned to work last Tuesday.

In June, he was accused of misconduct for having a civilian from outside the department transcribe audio recordings that were evidence in a murder case. The DA’s office cleared him of any criminal wrongdoing.