OAKLAND — In what is becoming a recurring theme at the Oakland Police Department, a rookie cop is under investigation by Internal Affairs, sources said Friday, on allegations of having sex in the basement of police headquarters on Seventh Street.

The revelations are another blow to a department recovering from a widespread sex scandal involving the teenage daughter of a police dispatcher and an investigation into racist and homophobic text messages between patrol officers and homicide investigators.

The troubling accusation surfaced as Oakland police officials acknowledged that another officer was recently arrested on suspicion of domestic violence, and officials and sources say that a criminal investigation has been opened after a large amount of narcotics removed from an evidence room more than a decade earlier was recently discovered in a locked cabinet at OPD.

In an internal document obtained by this news agency, police Chief Anne Kirkpatrick on Friday notified all OPD members of the incidents.

“I want to make it clear that I take these matters seriously and will not hesitate to hold those accountable who choose to engage in misconduct and violate the trust of the community and our law enforcement position,” the chief wrote. “We are in the business of regulating other peoples’ conduct, so I expect us to regulate our own conduct — on and off duty.”

Spokesman Officer Marco Marquez said that on May 27, the department received an allegation of “workplace misconduct” involving an officer. The department did not release the officer’s name or describe the misconduct, but multiple sources said he is a rookie who was hired in 2014. The sources said the officer had sex with a person in a basement office while off-duty. It’s unclear when the encounter took place.

Nearly a month later, on June 24, Officer Marcos Gocobachi was arrested on suspicion of felony domestic violence at a home in Richmond, police officials with Richmond and Oakland said. Gocobachi, 27, another rookie who joined the department in 2014, has not yet been charged, according to court records.

The next day, on June 25, police employees cleaning a basement office in Oakland police headquarters found narcotics in a locked cabinet, according to Marquez. The drugs, which sources said was a large amount that included cocaine and marijuana, were sealed, “and all contents were accounted for.”

Multiple sources said the narcotics were taken from evidence and stored in the cabinet more than a decade ago, and it’s unclear why they sat there. Sources said the drugs trace back to a lieutenant currently working in internal affairs.

For more than a year, the department has been dealing with the fallout from the sexual-misconduct scandal, which has resulted in criminal charges against one officer accused of having sex with the young woman while she was underage.

Two court-appointed attorneys, Edward Swanson and Audrey Barron, in a report issued last week, criticized the department’s handling of the case, first investigated after details of the sex scandal were revealed in a 2015 suicide note written by Officer Brendan O’Brien. Top police commanders, including then-Chief Sean Whent, knew of the allegations that officers were involved with the teen but conducted an inept investigation and did not notify the District Attorney’s Office for months, the attorneys wrote.

U.S. District Judge Thelton Henderson and monitor Robert Warshaw, who oversee the department’s federal reform program, ordered a new investigation that resulted in the discipline of 12 officers, including four who were charged with a variety of criminal offenses.

Civil rights attorney Jim Chanin said the department had been making reform strides before last year’s sex scandal set it back, and the recent cases could further hurt the department’s chances of ending the reform program.

OPD came under the watch of Henderson 14 years ago following the Riders police-misconduct scandal, a case in which Chanin and John Burris represented West Oakland residents who sued the city and accused a band of rogue officers of beating them and planting drugs.

“It’s an insult to the many hard-working officers at the OPD,” he said. “But most of all, it’s an insult to the taxpayers of Oakland who have to foot the bill for this unending series of atrocious and unacceptable conduct by some members of the Oakland Police Department.”

The offices of Mayor Libby Schaaf and City Administrator Sabrina Landreth did not offer any comment. Under an order from Henderson, the city will be forced to comment on the Swanson and Barron report before a July 10 hearing in the judge’s courtroom.