Now it appears three of the dead, his roomates, were stabbed to death. So knife, gun, car all used. The only "we have to do something" cries at the moment are of course of the "ban guns" variety. Probably by people who don't own guns, but own knives and cars.
I have never been exposed to people with severe mental illness, so I may speak from naivety, but the kid's final video seems more like a really bad farce or imitation of a B, or more likely C or D movie actor, with the forced maniacal laugh, etc. No doubt he was off his rocker, but if I would have watched the video pre this tragedy, without knowing any of the kid's history, I would have thought it was simply a poorly done, poor taste, social media joke.