Connor Betts was obsessed with violence and mass shootings

Why did he shoot his sister though? That seem cold blooded. I think maybe his sister knew about his mental health problem and probably called him a "weirdo" a "wacko" maybe he then got angry at her.

Or they were close and he killed her out of some twisted sense of empathy. He knew his act would ruin her socially and emotionally, which could not hold him back from committing it, so he zapped her too.