The Oakland Police Department, already reeling from a large-scale sex scandal involving several of its officers, announced Thursday that another officer was arrested and charged with soliciting prostitution and obstruction of justice charges in an unrelated case.

Oakland police said they arrested Ryan Walterhouse, 26, Wednesday night when he reported to work. Investigators say Walterhouse was placed under surveillance about three weeks ago after a colleague reported suspicions of Walterhouse to a supervisor.

Court records alleged that Walterhouse befriended a prostitute six to eight months ago and paid to have sex with in a Castro Valley, California, motel on Oct. 1.

He is also charge with warning the prostitute of police stings.

"You may want to call it a night," he allegedly texted her on Oct. 13. "They may or may not being doing something right now."

The next night he warned again.

"I'll let you know when to," he allegedly texted. "Not yet, they still out, probably after 12."

The Alameda County district attorney's office charged Walterhouse with two felony obstruction charges and a misdemeanor count of soliciting a prostitute.

"It is completely outrageous," Oakland Mayor Libby Schaaf said at a news conference announcing the arrest.

Deputy Chief John Lois said Walterhouse joined the department in 2014.

Walterhouse was released from jail early Thursday morning, Alameda County jail records show. It's unclear if he is represented by counsel. Oakland Police Officers Association President Barry Donelan didn't return a phone call or email inquiry.

Lois said Walterhouse's arrest was unrelated to the ongoing sex scandal involving the teenage daughter of a department dispatcher. The teen says she slept with 29 San Francisco Bay Area officers while working as a prostitute

Three police chiefs and four officers have been fired or quit the department since the sex scandal became public in June.

Alameda County District Attorney Nancy O'Malley said seven current and retired San Francisco Bay Area officers are being charged criminally for their alleged involvement with the teenager. Two officers have been charged with having underage sex with teenager.

The Associated Press generally doesn't identify victims of sexual crimes.