More data on mass killings:

Economists John Lott and William Landes conducted a groundbreaking study in 1999, and found that a common theme of mass shootings is that they occur in places where guns are banned and killers know everyone will be unarmed, such as shopping malls and schools.

I spoke with Lott after the Newtown shooting, and he confirmed that nothing has changed to alter his findings. He noted that the Aurora shooter, who killed twelve people earlier this year, had a choice of seven movie theaters that were showing the Batman movie he was obsessed with. All were within a 20-minute drive of his home. The Cinemark Theater the killer ultimately chose wasn’t the closest, but it was the only one that posted signs saying it banned concealed handguns carried by law-abiding individuals. All of the other theaters allowed the approximately 4 percent of Colorado adults who have a concealed-handgun permit to enter with their weapons.

“Disarming law-abiding citizens leaves them as sitting ducks,” Lott told me. “A couple hundred people were in the Cinemark Theater when the killer arrived. There is an extremely high probability that one or more of them would have had a legal concealed handgun with him if they had not been banned.”