Supply teacher=Subsitute teacher.
If he wanted to avenge his mother, why’d he kill her, too?
She may have been trying to stop him from getting guns. Or perhaps she did not want him to carry out the plan he told her about. She had pulled him out of High School because she did not agree with the way the school was handling him. So why would he not then got to the High School ? How old was he when he graduated from Elementary School ? He was 20 and still in the 10th grade ?