His first victims were his mother and stepbrother. Then he slaughtered students at a school he dropped out of at age 14. He started trans-ing at age 12.
Connecting dots that may not have been in real life, it sounds like things did not go well with his sexual identity thingy, it did not go over smoothly at home, and went much worse for him at school (12YO-14YO can be pretty cliquey, "intolerant" of people who are different, and thar be bullies) Sounds like he got "revenge" on his family, the school, and finally on himself. My guess and a tenner will get you a latte at Peet's or Dutch Bros and change.
His welcome to eternity was probably "warm" and less than pleasant.