A Lebanon man who was incarcerated for allegedly sexually assaulting a 12-year-old girl died Monday night at the MacDougall-Walker Correctional Institution in Suffield, an apparent suicide, according to a release from the state Department of Correction.

Robert Chesters, 42, was in custody after his Sept. 27 arrest on charges of first-degree sexual assault and risk of injury to a minor.

At approximately 8:31 p.m. Monday, correctional staff discovered Chesters unresponsive in his cell with one end of an extension cord tied around his neck and the other end secured to the bunk bed. He was the only inmate in the cell at the time.

Correctional and medical staff immediately initiated emergency and life-saving measures, the release said. Chesters was taken to St. Francis Hospital in Hartford, where he was pronounced dead at 9:55 p.m.

The exact manner and cause of death will be determined by the State Medical Examiner’s Office. The Department of Correction and state police are investigating the death.

According to an arrest warrant affidavit, school officials contacted state police at Troop K in Colchester in September after several students in an unnamed school approached administrators to report that a classmate was involved in a sexual relationship with an older man.

Approached by investigators on Sept. 10, Chesters, who was a widower, said that he and the alleged victim, a friend of his teenage child, started texting each other, and the texts escalated emotionally and sexually.

As they continued to investigate, troopers were called to Chesters’ house on Sept. 11 and found him unresponsive in the front driver’s seat of his pickup truck. He smelled of alcohol, according to the affidavit. Chesters was taken to Windham Hospital because police believed he was a danger to himself.

While taking an inventory of his belongings, troopers found in his pocket a suicide note he had written to his family and to the victim, in which he apologized for being in love with the girl, according to the affidavit.

The alleged victim reported that the sexual relationship started in August. She said Chesters, whom she called Bob, told her that if people found out about their relationship, he would go to prison for 10 years. She said Chesters would give his own teenage child Benadryl for allergies so the teen would sleep soundly while she had sex with him during sleepovers at Chesters’ house.