Also perhaps worth noting: when he entered his most recent residential facility, he was the first planned-school-shooter they'd ever had. By the time he left today, he was one of three.

It's a problem.

Is the school aware of his hobby?

The old school certainly was--one hospital notified local police after his biological mom refused to cooperate with medical professionals, and the sergeant assigned to the case was the permanent officer at the high school. When my stepson was transferred from one facility to another, it was in the back of this police officer's vehicle. He definitely can't go back to the old school, but the district as a whole has to take him as long as he hasn't done anything expellable.

We're unclear as to how far Bio Mom has moved forward with her choice of new school. It may be wishful thinking on her part. The district may know everything at an upper level already, and tell her it's the disciplinary high school or nothing. Or they may have their hands tied as well, if she can get a medical professional to sign off on him being stable. As of right now, he's transferring to a day program that allows him to sleep at home at night, but that only happened after Bio Mom was informed that her first choice of an afternoons-only day program (so he could jump back into school immediately) was medically unacceptable. The all-day-program may keep him for up to several months, but by August he'll definitely be in full-time school again if she has her way--or, possibly he'll have snapped again and be back in a facility, or jail, or dead.

The best I can realistically foresee happening is he attacks someone non-lethally before his 18th birthday, so he's tried as a minor and spends the rest of his life in a mental hospital. All other scenarios have worse outcomes for both him and everyone else. I'd love to be an optimist and say he keeps this thing under control and lives a productive life, but I've talked to him for too many hours about this stuff and I don't believe it's possible.

From what you've written, it seems unlikely he'll attack just someone as he seems interested in numbers. He also seems interested in the killing more so than doing it by shooting. Restricted access to firearms and explosive materials may delay acting out; but, maintain awareness of alternate methods based upon availability and simplicity - like a chemical attack!

Nothing fancy, just old fashioned mass poisoning via contaminated foods or beverages at a gathering. There are plenty of products in the home and on store shelves that can be lethal if ingested. Let others be your taste testers when he's around and keep the poison control center number handy. Don't become collateral damage.