In the case of Kemper he also had issues with other female family members. It's ironic since he already was in a psych ward for shooting his grandparents but also due to lobbying by his mother and him learning the right answers to evaluation questions he was released early.can't these guys just kill their abusive bitch moms instead of murdering women who never harmed them?
edmund killed his mom but only after killing a bunch of innocent women
By his teens the guy was fundamentally broken and regularly tortured and killed animals. He later upgraded to killing humans. Whether that's due to the abuse or genetics is an open question.