TRENTON, S.C.  — A 60-year-old man who strangled his girlfriend died of a heart attack while burying her body in their South Carolina backyard, investigators said.

Deputies found Joseph Anthony McKinnon’s body Saturday after neighbors called and reported an unconscious man in a yard in Trenton, the Edgefield County Sheriff’s Office said in a statement.

As they investigated McKinnon’s death, deputies found a body wrapped in trash bags in a freshly dug hole and determined it was his girlfriend, Patricia Ruth Dent, 65, investigators said.

An autopsy on Dent determined she had been strangled and neighbors told officers they saw McKinnon digging a hole in his yard the day before, deputies said.

An autopsy on McKinnon determined he died of a heart attack. Deputies said it appeared he was nearly done filling the grave when he set the shovel down, walked away and collapsed.