From the shooter:
I'm a girl who's been trapped in a man's body for two and a half decades, and I need to get the hell out. I don't belong on this planet, nor have I ever. I need to die, and I'm taking whomever I can down with me."
From a quick google:
TL;DR(the news) big meanie was a wannabe animator that made some shitty thing involving his waifu ember from Danny Phantom. Had Massive online presence for that thing including Twitter accounts for his all his OCs. Was convinced he was some cartoon ghost possessing a dude's body. Apparently the only way to free himself was to kill himself, but he's such a big meanie he had to take a couple of people he hated with him. Reading back on his online history it seems completely obvious he'd go postal. Apparently he didn't shoot his parents because he wanted them to suffer in the aftermath.
Andrew Blaze
Sooooo - paranoid delusional guy that's convinced he's a female waifu trapped in his boring suburban dork body. So he shoots every one.
The common string is always some isolated young man that shows all signs of mental health problems and everyone pawns it off as "quirky" or whatever.
We need both mental health services, but we also need the cultural shift to be allowed to say, "yo, Andrew is legit strange and needs to be checked on. Something seems more than the average nerd hobby". Not every one is just a spectrum of quirky. And watching ANY of his videos shows serious mental health problems.