AUGUSTA – An investigation is under way in the rape of a female patient at the Augusta Mental Health Institute, according to police.

The woman allegedly was assaulted Saturday evening by a male patient living on the same floor, police said.

An AMHI staff member saw the suspect leaving the woman’s room and told him to go back to his own room, police said. The staff member then checked the woman’s room and said she appeared to be sleeping.

Staff members were not aware of the assault until the woman confided in a staff member the next day, police said.

Advocates for people with mental health are criticizing the way AMHI handled the incident, saying too much time elapsed between when staff members were told about the assault and when they called police.

“Minutes can make a difference,” Augusta police Lt. Dennis Passmore told WMTW-TV. “It depends on whether the victim has bathed or somehow contaminated the evidence. So time is always a factor.”

Passmore said the woman is 31 years old, and the suspect is 20.

As at many hospitals, most patients at AMHI have individual rooms without locks and live in coed units, said Lisa Kavanaugh, AMHI’s superintendent.

The woman was moved to a separate unit at AMHI after the assault was reported, Kavanaugh said, and both she and the suspect are being monitored at all times for safety reasons.

Kavanaugh said the facility would conduct an internal investigation into the incident.

No instances of sexual assault have been reported at AMHI in about 15 years, police said.

In February, the Joint Commission on Accreditation of Hospital Organizations gave AMHI high scores in several areas, including medical and psychological services and environment in which care is given.