COLLEGEVILLE, PA (CBS) — A 68-year-old former teacher’s aide at Conestoga High School, who pleaded guilty to child sexual assault, was found dead in his Graterford prison cell earlier this week.

Arthur Phillips was working in the TV production studio at Conestoga High when he sexually assaulted a girl over a period of months.

In November, Phillips pleaded guilty to involuntary deviate sexual intercourse, aggravated indecent assault and other charges. He was sentenced to 10 to 20 years in state prison.

The Montgomery County Coroner’s Office lists the cause of death as suicide and says Phillips hung himself.

ALSO READ: Man Admits Killing His Mother During Thanksgiving Weekend

Investigators say Phillips groomed the girl, starting when she was 15. They say she tells them she rejected his advances, but that didn’t stop him.

When the investigation began, Phillips crashed his car in what was believed to be an attempt to take his own life. A note inside the car said, “I was just a guy trying to help a kid and the boundaries just got gray.”