OAKLAND, Calif. (AP) — An officer’s suicide prompted an investigation into allegations that Oakland police officers committed sexual misconduct with a minor, the department’s police chief said Friday.

Oakland Police Chief Sean Whent did not specify how Officer Brendan O’Brien’s suicide in September led to the sexual misconduct probe by the department’s internal affairs division. O’Brien killed himself a little more than a year after police say his wife, Irma Huerta-Lopez, also took her life.

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The sexual misconduct allegations are the latest blow for a police department that remains under federal oversight, and a U.S. district court judge expressed concern in a March order that the internal affairs probe could affect the department’s ability to demonstrate “commitment to accountability and sustainability — both of which are key to ending court oversight.”

City officials said Friday the Alameda County District Attorney’s office will conduct its own investigations of O’Brien and his wife’s suicides and the sexual misconduct allegations and review the city’s investigatory process. The allegations have prompted the department to put three officers on administrative leave. Whent declined to say whether other officers have been implicated, only saying the investigation was ongoing.

“The allegations in this case are extremely troubling ...,” he said. “We want to ensure that all of our employees are of the highest moral character and conduct themselves professionally, not only on duty, but off duty as well.”

Huerta-Lopez’s family told the East Bay Express newspaper that they believe O’Brien shot his wife. Police on Friday defended their investigation of Huerta-Lopez’s death, saying her hands tested positive for gunshot residue, and there were no signs of other trauma to her body or a struggle in the apartment.

Whent said he was skeptical when he initially heard she had committed suicide, but the department investigated the case thoroughly.

The department is overseen by a federally appointed monitor as part of court-mandated reforms to settle a multimillion-dollar lawsuit alleging widespread misconduct by a notorious group of police officers known as “The Riders.”

The group was accused of beating and framing suspects in the West Oakland more than a decade ago. The settlement included 51 specific reforms the department agreed to make within five years.

In his March order, U.S. District Court Judge Thelton Henderson, who is overseeing the reforms, directed the monitor to use his authority to ensure that the sexual misconduct allegations and “any related matters are properly and timely investigated, and that all appropriate follow-up actions are taken.”