(MCT) — Christopher Vaughn's attorneys tried Monday to bolster their theory that his wife murdered the couple's three children, telling a judge that their oldest daughter told a classmate her mother "was hearing thoughts in her head" and was a "psycho."

Vaughn, 37, is scheduled to go on trial in August in the handgun slayings of his wife, Kimberly, and their children, who were shot inside the family's vehicle on the way to a Springfield water park in 2007. His attorneys have argued Kimberly shot the children, tried to kill her husband, then shot herself.