My husband actually used to work on this kind of technology. It's much harder than you think.
That's exactly why I think it's what happened. Most of these spree killers are looking for infamy. You know troubled, loner teenagers from a down-and-out town especially would have reason to try to reach "legend" status, and considering they were "raised by the internet," on the internet (especially the 4chan kind of communities they were probably part of) a lot of times fame and infamy are the same thing. If they had committed the murders, torched the victims' van and escaped, they would have easily gotten away with it but nobody would know who they were. They clearly wanted people to know they were the killers. If they had killed themselves in an area where they would be found, or been killed by police, nobody would care about this news story after a few days. Life as a fugitive sucks and they could be captured at any time, thus shattering the illusion of them as mastermind criminals. By killing themselves where they could never be found, it gives a ton of attention to them, and always leaves the question open of "what if they really did escape?" Plus they obviously didn't value their own lives (or other peoples' for that matter) very much anyway since they threw them away that easily.