Austin Cook was sentenced to 2 years of community service and 8 years of probation after making a similar threat, albeit without as much evidence:
Jared Cano's attorney discusses options after judge issues 15-year prison sentence
That, plus counseling help, seems more appropriate. It looks like the rough upbringing had a fair amount to do with this (these type of things tend to be related to emotional/mental state, and they certainly appear to be here).
I know of a couple somewhat-related cases in real life, and in both cases things wound up okay without prison. Even the bloke who had a hit list, got caught, etc., went to a juvenile re-education type program for a couple years, but was able to return to school eventually, make some friends, graduate, etc. in much better condition. Last I heard, he's a productive member of society.