Chris Colwell, director of emergency medicine at Denver Health, has treated victims from two of the deadliest mass shootings in the U.S. He says he's deeply disturbed by how easy it is to get guns.
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Police gathered at the east entrance of Columbine High School in Littleton, Colo., on April 20, 1999, after two teen students went on a shooting rampage before turning the weapons on themselves.
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