Connor Betts, 24, had a hit list of classmates and a rape list of girls.
Betts was suspended at Bellbrook High School after a hit list of those he wanted to kill was found in a school bathroom.
The gunman had a history of violence.
He killed nine people outside a crowded bar on Sunday, injuring dozens.
Among the nine people killed was his sister.
Police said a cheerleader at the school was also included on the list of targets.
The woman said she didn’t know Betts and was surprised when a police officer told her she was on his rape list.
Police said there was nothing in the 24-year-old’s background that would have prevented him from purchasing the gun with extended ammunition magazines.