Arla "Caroline" Christensen, 85, was dead in one of the bedrooms. On the bed lay a metal rod later identified as a golf club with a missing head.
The defendant's wife, Angela Cuillard, told officers her husband was having a psychotic episode and had beat her grandmother to death with the club, according to documents.
The wife said she saw her husband come out of the garage of their home holding a golf club and walk into her grandmother's bedroom. He closed the door and locked her out of the room, documents state.
After telling her two juvenile children to flee the home, Angela Cuillard returned to the now-unlocked bedroom and found her husband kneeling over the elderly woman's unmoving body. There was blood on the closet door, documents say.
Christensen, who appeared to have been bludgeoned about the head, was declared dead at the scene, according to Sandy police.
Christensen had moved in with her granddaughter sometime during the past year due to health problems, Sandy police Sgt. Jon Arnold said. She previously lived in Mount Pleasant.
In an interview with Sandy police, Cuillard admitted the blood on his clothing was "grandma's," according to jail documents.
He also told police that "he had to do what he did to make things better," the jail document says. "In his mind, had he not done it, things would have been worse."
Cuillard's wife told officers her husband has a history of "severe mental illness" and had not been sleeping in the days leading up to the alleged crime.
Cuillard is being held without bail at the Salt Lake County Jail.