After a Seminole County man slapped his wife, his son-in-law walked into the room and shot him dead, according to the county Sheriff’s Office.

Shaun Paul Simon, 42, was arrested Wednesday on a charge of first-degree murder in the killing of 80-year-old Bill Toth. Simon lived with Toth outside of Sanford along with his wife and her mother, according to his arrest report.

Deputies responded to the home Tuesday after Simon’s wife called 911. Seminole County Fire Rescue was already on scene treating Toth, who had been shot in the chest. He was taken to a hospital, where he died of his injuries early the following morning.

Simon was identified as a suspect and detained.

Simon’s wife and mother-in-law told deputies Toth had been showing signs consistent with dementia for months, which had caused turmoil within the home. There had also been suspicions Toth had been unfaithful to the mother-in-law. Both said Toth had slapped the mother-in-law Tuesday evening, according to the report.

When the mother-in-law entered Simon’s bedroom to tell him and his wife about it, Simon appeared visibly upset and left the room to confront Toth. Shortly thereafter, the two women heard a loud bang and exited the bedroom to find Toth lying on the kitchen floor and staring blankly at the ceiling, the report said.

Simon admitted to deputies he shot Toth in the kitchen, telling them he decided to do so upon hearing he hit the mother-in-law. He said he placed a blanket over Toth’s face after shooting him. Simon described the man as a narcissist who “had been making his life miserable,” the report shows.

Simon is currently in custody at the Seminole County Jail. His arraignment is scheduled for March 24.