There are certain topics, like guns, that come up over and over again in the wake of mass killings like the one in Isla Vista. 

Things like mental illness, or a culture of violent video games, are looked to for explanations, but what other factors connect the perpetrators of these crimes?

Graduate student Cliff Leek and sociology professor Michael Kimmel have studied the profile of mass shooters and found a striking commonality: they are overwhelmingly white and male. Cliff Leek joins us now with more.