After the deadly shooting in Newtown, Conn., Dr. Charles Catania sent The Rachel Maddow Show a graph revealing the number of people killed in the 12 deadliest mass shootings in the United States.
The grey area shows the time when the U.S. had a law banning most semiautomatic weapons, which can shoot relatively quickly because they don't have to be reloaded after each round.
That law expired in 2004, and since then mass shootings have gotten deadlier every year. See for yourself:
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