By Mayra Cuevas and Holly Yan
(CNN) -- An Oklahoma City police officer is accused of sexually assaulting several women while on the job, his department said.
Officer Daniel Holtzclaw, 27, was arrested Thursday and faces nine charges, including three counts of forcible oral sodomy, two counts of indecent exposure, two counts of rape and two counts of sexual battery, according to the Oklahoma County Sheriff's Office.
The case started after one woman came forward and accused Holtzclaw of "sexual impropriety" during a traffic stop, Oklahoma City police Capt. Dexter Nelson told CNN.
After that woman's complaint, investigators started looking into all of Holtzclaw's traffic stops for other potential victims, CNN affiliate KOKH said.
Nelson said authorities found six other victims. He said some of the women "were initially less than cooperative, but investigators were able to gain statements," he said.
Officials said all the alleged attacks took place during traffic stops, CNN affiliate KFOR reported.
The city's police chief said there may be more.
"We kind of anticipate there may be more victims out there because this goes back to February -- February was the earliest that we have here, through June," Oklahoma City Police Chief Bill Citty told reporters.
"If there's anyone that was victimized by this officer, we certainly want to hear from them."
It was not immediately clear whether Holtzclaw had an attorney. His bond is set at $5 million.
CNN's Darrell Calhoun contributed to this report.
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