An occupational therapist was arrested Friday on a charge of sexually assaulting a patient in 2012 at a Prince William County military clinic, police said.

Robert Edward MacDonnell, 44, is accused in the attack, which happened in September 2012 at the Dumfries Health Center, 3700 Fettler Park Drive, according to authorities. Police said MacDonnell, who lives in Purcellville, is being held without bond.

Authorities said they started investigating a report of the attack on Dec. 19, 2013, and concluded that MacDonnell had sexually assaulted a 21-year-old woman from Woodbridge at least once while he was caring for her in 2012.

MacDonnell works for Spectrum Healthcare Resources, which has placed him on administrative leave until the end of the investigation, said Tracy Young, a spokeswoman for the staffing agency.

A spokesman for Fort Belvoir Community Hospital, which is affiliated with the health center, said in a statement that the hospital is aware of MacDonnell’s arrest and is cooperating with military and civilian investigators. Chris Walz, the spokesman, declined to comment further, citing the ongoing investigation.

A court date was unavailable for MacDonnell, according to police.

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