Investigators charged a man with murder in the killing his girlfriend in their South Carolina home, but he says the gun went off by accident.

Sumter County Sheriff Anthony Dennis told The Item of Sumter that 45-year-old Beverly Thomas was shot in the head in her Rembert home Saturday night.

Deputies arrested her live-in boyfriend 29-year-old Derrick Shannon at the scene.

Dennis says the couple were arguing during the day, but says Shannon told investigators he found the gun a few weeks ago and was trying to clean it when it went off, striking Thomas as she cleaned the shower.

Shannon also is charged with being a felon in possession of a handgun. It wasn't immediately clear if he had an attorney.