David McNew

Christopher Harper Mercer, who killed nine people and injured nine others last week at Umpqua Community College, owned a total of 14 guns. Adam Lanza, who killed 20 children and six adults at Sandy Hook Elementary, had four firearms with him on the day of the massacre and three additional guns at home. James Holmes, who killed 12 people and injured 70 others at a movie theater in Aurora, Colo., had four guns, all purchased legally in the six months prior to the shooting.

Three men, three personal arsenals. And according to a forthcoming study from the Harvard Injury Control Research Center, they aren't outliers. The survey of 3,000 people found that 25% of gun owners reported having five or more firearms, and 8% of gun owners had 10 or more firearms. (Harvard's last study in 2004 found that 48% of gun owners reported owning four or more guns.)

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“These are people who do buy guns and have a lot of them,” Dr. David Hemenway, director of the research center, told the Trace. “So we have to wonder, who are these people and why do they have so, so many guns? What’s the purpose of it? And are they really responsible?”

And Hemenway had his theories about who these gun owners might be. “By far, the most likely person to be a gun owner is a white male," he said. "So it would be surprising if it was somebody else.”