Now, that I'm reading the story and reflecting on it, we do not have the facts of what happened and perhaps never will given the perpetrator's age. Nonetheless, here is some speculation:
The Frickers, I would hope would be carrying a concealed weapon and if they were not which it appears to me, let this be a lesson for others. I don't mean this in a heartless or senseless way. I know of another news story of a few years ago, where the head-of-the-household, shot a young male in the bedroom of the daughter of the house and I'm rather sure, that head-of-the-household never had charges press against him. It was a case of self-defense it was decided.
Secondly, the unidentified male in this case, tried to kill himself and some stories say his condition is "life-threatening", so, I imagine this teen is in very bad shape and perhaps even has "brain damage". See:
https://patch.com/virginia/reston/nazi-boyfriend-center-reston-triple-shooting-reportIt's a very disturbing story and the two killed were surely, very decent people. My prayers go out to those affected by this tragedy.