Deborah Blum of the Knight Science Journalism Tracker has a great roundup of answers to the question: “Why would someone, anyone, buy four semi-automatic weapons and 6,000 rounds of ammunition for the single-minded purpose of harming people he did not know?”
She links to a fistful of well-researched articles making it clear that most of our presumptions about mass killers from Columbine on are wrong, or at least drastically oversimplified.
We may never know what actually motivates someone to slaughter a bunch of strangers, but we do know what makes it easy for them to do it: America’s laissez-faire gun laws. Mother Jones looked into the biggest mass murders of the last 30 years and found that “of the 132 guns possessed by the killers, more than three quarters were obtained legally.” (Are you listening, President Obama?) MoJo has posted an excellent clickable map showing where each of the killings happened and who it involved.