SACRAMENTO, Calif. -- A Sacramento police officer is under arrest, charged with a number of crimes that allegedly occurred while he was on duty.

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After a police investigation, Chief Arturo Venegas (pictured, right) announced the arrest Monday of Officer Darryl Rosen.

"I stand before you today saddened that I have to announce the arrest of a Sacramento police officer. After an extensive investigation by our department and at our request, the Sacramento District Attorney's Office made a determination that there was probable cause to arrest Officer Darryl Rosen for on-duty criminal misconduct," Venegas said.

Rosen, a 5-year veteran of the police force, is facing one count of felony rape, four counts of felony sexual battery, eight counts of assault by a public officer, one misdemeanor count of sexual battery and three misdemeanor counts of false imprisonment.

"All of the evidence indicated that this officer acted alone when he committed the alleged crimes," Venegas said.

The chief said that the department undertook an "exhaustive investigation" into Rosen's on-duty behavior that utilized 18 investigators, put him under surveillance and contacted multiple citizens.

Authorities said that there are five alleged victims in the case, but detectives said that there could be more.

Rosen has been on paid administrative leave for several months during the investigation.

"As a result of this incident and the investigation, we are taking an internal look into our hiring and supervision of Mr. Rosen," Venegas said.