Jon E. Yount, 74, had been in good health before he was found hanged in the state prison in Greene County, Pennsylvania on April 26.
His suicide came just three days ahead of the 46-year anniversary of his gruesome crime.
On April 29, 1966, he stopped 18-year-old Pamela Sue Rimer as she walked home from her school bus stop.
He was her maths teacher at the Dubois High School, where she was a senior, but she had been trying to get out of his class as she disliked him.
Yount beat, raped and stabbed Rimer before slitting her throat and leaving her to die in a wooded area near her home in Luthersburg. Yount left the scene, burnt his clothes and collected his children from their babysitter.
Rimer was buried in her prom dress and classmates laid their graduation tassels across her grave.