OAKLAND — Sex. Suicide. Murder? A sex scandal involving Oakland police officers and a young woman who touts her law enforcement liaisons on Facebook has all the makings of a TV thriller, full of twists and turns.

Three officers were placed on paid leave this week, months after Officer Brendan O’Brien committed suicide and left a note spilling the details — including names.

Adding to the intrigue, O’Brien’s wife, 29-year-old Irma Huerta Lopez, also committed suicide, on June 16, 2014, by shooting herself in the head with her husband’s gun.

Lopez’s death was briefly investigated as suspicious but then ruled a suicide, according to the Alameda County coroner. Not that it convinced her sister or her family, who blamed O’Brien.

“I always knew it,” Paulina Huerta said Friday. “It was not possible for my sister to kill herself. But we didn’t have proof.”

Top city officials on Friday confirmed the gun that killed Huerta Lopez was fired twice — one bullet hit the floor, the other struck her head — and both O’Brien and his wife tested positive for gunshot residue on their hands. According to the coroner’s report, the two had argued the night of the suicide, before he left the home and returned to find her dead.

Although police Chief Sean Whent and Lt. Roland Holmgren of the homicide unit said it is not uncommon for both of those things to happen, the city announced Friday that the Alameda County District Attorney’s Office has been called in to review both suicide investigations and the ongoing sexual misconduct investigation.

Whent said the investigations into the deaths were thorough, and evidence supports the suicide rulings in the case of O’Brien and his wife.

Mayor Libby Schaaf called for the district attorney investigations and said no DA employees who used to work for the police department will be a part of it.

“We as Oaklanders can expect to hold officers to the highest standards of conduct — again, both while they wear a uniform and when they do not. And that is a standard that we intend to enforce in the city of Oakland,” Schaaf said Friday, clearly angry.

Whent and Schaaf declined to discuss the sexual misconduct investigation. The exact allegations have not been released.

But a source said O’Brien in his suicide note confessed to exchanging messages with a young woman who goes by the name Celeste Guap but did not have sexual contact with her. In the note, O’Brien named the officers, including one sergeant, involved in the alleged sexual misconduct with Guap, who is the daughter of a Oakland police dispatcher. The police investigation will look at whether Guap was under age during some of the encounters with officers.

Attempts to reach the woman at the center of the scandal through a relative were not successful, but she has been posting about the allegations on Facebook, the same place sources said she has met multiple officers.

This week, she wrote, “the only officer I ever messed with underage is sadly gone now, so I don’t know why this is still being brought up.” In another of her posts in late April, there was a picture of an Oakland patrol car parked at gas station with a message: “took me back to Richmond in style #saucy.”

Sources and a coroner’s report said O’Brien’s life went into a downward spiral after his wife’s death. A U.S. Marine who served in Afghanistan, O’Brien was diagnosed with post-traumatic stress disorder and was distraught over his wife’s suicide before shooting himself, according to the report. He admitted in the suicide note that was drinking heavily and suffered from lingering suspicion that he might be involved in his wife’s death, despite being cleared, a source said.

“O’Brien did not have a history of suicide attempts, but according to the note of intent he left at the scene, he was suicidal and a series of events regarding his wife and work prompted him to commit suicide,” the coroner’s report said.

Calls and messages to the O’Brien family were not returned.

U.S. District Judge Thelton Henderson, who oversees the department’s court-mandated reforms stemming from the 1999 Riders police-brutality scandal, issued an order in March saying there were “irregularities” and “violations” of procedure in the handling of the sex allegations by police. The judge wrote that it raises concerns about the department’s “commitment to accountability and sustainability.”

Schaaf has asked the department to report to the DA’s office each time an officer is suspected of criminal misconduct. Whent, citing recent arrests of two officers while off-duty, said the department will review misconduct cases in recent years to look for patterns and see if leaders can prevent future cases.

“We want to ensure that all of our employees are of the highest moral character and conduct themselves professionally, not only while they’re on duty but off duty as well,” the chief said.

Staff writer Katrina Cameron contributed to this report. David DeBolt covers Oakland. Contact him at 510-208-6453. Follow him at Twitter.com/daviddebolt.