Ira and Barbara Clemons were found dead in their beds from apparent gunshot wounds. The body of their son, Allen, was found in the basement with a gun nearby.
Police said Allen had a history of strange behavior. Detective Don Jolly from the Pekin Police Department said unusual markings discovered inside the house are raising concerns.
"There was some red spray paint inside on the walls, you can see there's a few crosses spray painted inside the house," he said. "There's basically gibberish with religious undertones painted on the walls. You can tell it was obviously someone who psychologically had some issues."
Police said all three victims lived in the home and they aren't looking for a suspect in the case.