STEWARTSTOWN, N.H. — The body of an 11-year-old New Hampshire girl who disappeared almost a week ago was discovered Monday in a river less than half a mile from her home, and authorities said they considered her death suspicious.

Celina Cass was reported missing July 26. N.H. Fish and Game Department divers found her body Monday near a hydroelectric dam that spans the Connecticut River between her hometown of Stewartstown and Canaan, Vt., said Senior Assistant Attorney General Jane Young.

Authorities said that Celina, who lived with her older sister, mother and stepfather a mile from the Canadian border, was last seen at her home computer around 9 p.m. on July 25 and was gone the next morning. Police said there was no sign of a struggle, and there was no indication she ran away or that someone took her.

An autopsy was scheduled for today to determine the cause and manner of death. “Based on what we have seen visually, we are treating it as suspicious,” Young said.

According to several media outlets, Celina’s stepfather was taken to a hospital Monday. MSNBC reported that Wendell Noyes was taken by ambulance after repeatedly lying down in the family’s driveway and rolling around, and video showed him dropping to his knees in the driveway and then lying face-down, with his head resting on his hands.

In 2003, Noyes was involuntarily committed to New Hampshire Hospital in Concord after he entered his girlfriend’s house in the middle of the night and threatened to throw her down stairs, according to court documents. An order signed by a probate judge indicated Noyes suffered from paranoid schizophrenia and believed corrections officials implanted a transmitter in his body to keep track of him.

A court motion filed by his attorney at the time indicated Noyes served in Operation Desert Shield before receiving a medical discharge from the Air Force because of schizophrenia.