My recommendation to people interested in what happened, in the sense of how this man stepped out of his isolation and alienation to murder nine people, is to keep following the story after it falls out of the big media news cycles.
The authorities so far (next day) are being a bit closed mouth about the details. Chris Mercer was obviously not your routine 26-year-old, so the question remains as to what it was that sucked him down into the vortex of a compulsion to kill as many people as he could.
I followed the case of James Holmes (the mass killer in the Aurora, Colorado movie theater shooting) well beyond the initial media uproar, and wonder how many people learned that Holmes had been seeing a University of Colorado psychologist and that he had, in fact, threatened her. She knew he was dangerous and reported it to university officials, but when he was dumped out of the university neuroscience program and out of the university itself, there was no indication at all that the university told local police that Holmes was a threat.
In other words, Holmes had been in the mental health net, but he didn’t slip through it. He was tossed out of it. The university was hoping to be rid of him, and that was that.
So, follow the story beyond the immediate horizon. You can do that by continuing to do Google searches on it when it starts to disappear from the national media. You’ll get the local, regional, and state news reports.
I don’t expect the Mercer case to resemble the Holmes case, but I do expect that there will be a lot more to his story than will be caught in the current avalanche of coverage. And that having an intelligent discussion of his case and the problem of mass shootings will be impossible without those details.