Coroner Sabrina Gast said Tuesday autopsy results show 34-year-old Matthew Grose died of blunt force trauma to the head.
Grose was arrested in October and charged with running over 53-year-old Sandra Thomas, then beating up and running over his mother, 65-year-old Sandra Grose. Both were found dead in their yards.
Authorities have said Grose was combative and repeatedly hurt himself after his arrest, trying to drown himself in a jail toilet and hitting his head against the wall before officers put him in a restraint chair.
Gast says Grose had bleeding on the surface of his brain and in tissue that separates the brain from the skull.