Man I can't imagine how bad be saw his life to go through with that given what he had and what he could have.
I don't say this glibly: Try being depressed. There is a segment of the population for whom these things are all too understandable. No less tragic for it.
I read "The Teenage Brain" a couple of months ago. It's #1 on my must-read list for anyone who has or will have or is interested at all in adolescents. It was written by a Harvard neurologist, and it goes through the brain's life cycle in purely physical terms. The takeaway: We as parents, and often the kids themselves, have shockingly little control over what's happening in there. The brain simply isn't ready to make rational decisions.
(tl;dr Don't yell. They won't take your message and all you'll do is feed the dangerous impulses.)
It scared the daylights out of me and it will until my youngest child, who is 5 now, is in his mid-20s at least.
Regarding concussions, love gone bad or anything else, I'm not dismissing those as possible factors, but there could have been a million things going on. Sleep patterns could have contributed. Marijuana use could have contributed. (Read that chapter and you'll be a YankeeFan convert -- pot is really, really bad at that age.) Hell, he could have been pissed about a grade, and the impulses got ahead of the reasoning as is normal at that age, and he does something that can't be undone.
It's a frightening time. I never felt it when I was that young, I know others did, but it's one area where we're starting to know how much we don't know.