BENNINGTON, VT. ? For years, a man regularly confined his adolescent stepson to a bedroom rigged with an alarm, molested him several times a week and often denied him food, water and access to a bathroom, authorities said.

The 17-year-old boy, who lived with his stepfather for nearly six years, told police Robert J. Pratt would smash his head into a wall when he resisted his advances and sent him to school in long-sleeved shirts and pants so no one would see his bruises and scars.

Pratt was being held without bail on sex assault charges, accusations that surprised acquaintances who know him as a quiet, helpful neighbor.

The boy came forward after Pratt, 37, of Bennington, kicked him out of the apartment they shared and he moved in with his mother, who lived in the same apartment complex.

Once there, he told her and a counselor about his life with Pratt. He had moved in with him when he was 10 or 11, when Pratt and the mother split up. He said the abuse started about a year later and he never told anyone of it because Pratt threatened him, sometimes with a loaded gun.

Investigators, trying to verify the boy’s claims, had the boy wear a wire to record a conversation with Pratt. In that conversation, the victim asked Pratt why he sexually abused him.

“I have tried to block that out,” Pratt replied.

Questioned by police, Pratt didn’t deny the sexual activity but attributed it to the victim’s “desires,” according to an affidavit filed by Vermont State Police Trooper Tyler Burgess.

Police say Pratt sometimes threatened the boy with a loaded rifle, threatened to kill him or grabbed his genitals, asking “Whose is this?” as he pulled.

“I’d have to reply ‘yours’ or he’d pull harder,” the boy told investigators.