A 15-year-old teenager allegedly killed his father, then set their home on fire because he was afraid his father would find out he was failing some classes, prosecutors said. Ryan Watts was charged Friday with murdering his father, 50-year-old John E. Bruner, who was initially believed to have died in the fire earlier this week. He was charged as an adult. Watts was arrested Wednesday after an autopsy determined that Bruner died from multiple gunshot wounds and not from the fire, Santa Clara police said. According to court documents, Watts told police he took a .45-caliber handgun from a safe in his father's bedroom and stashed it in his room shortly before the killing. Court documents allege he shot his father in the head at close range Monday, then set the body on fire because it was too heavy to carry to the backyard, where he had planned to bury it. Watts hid the gun and went to a Taco Bell fast-food restaurant before calling emergency services to report the fire, the documents said. Watts' parents apparently were separated, and he had been staying at his mother's home since the fire, police said. If convicted, Watts faces life in prison. He is not eligible for the death penalty because he's a juvenile. Watts is expected to enter a plea during a Dec. 22 court appearance.