GEORGETOWN, Ohio (AP) — A 400-pound Ohio man who pinned his 11-year-old step-grandson against the arm of a couch while trying to control the boy with mild autism during a tantrum has pleaded guilty to killing the boy.

Fifty-eight-year-old Donald Martin Jr., of Mount Orab, entered a plea Thursday to a reckless homicide charge in Brown County.

Brown County sheriff’s Sgt. Chad Noble on Friday called Dylan Dylan’s death a “tragic accident.” He says Martin tried to intervene when the 90-pound boy began acting out last November.

Dylan’s grandmother called 911 to report that the boy had passed out after a tantrum. He was pronounced dead at a hospital.

A coroner ruled that he died of positional asphyxiation.

Martin’s attorney couldn’t be immediately reached for comment Friday. Sentencing is scheduled for May 8.