Take a look at some of the worst mass shootings in U.S. history.
Sources say close to 30 people were killed, many of whom were children, during a school shooting the Sandy Hook Elementary School in Newton, Conn.
Brendan McDermid/Reuters
Boy Scouts of America
Ed Zurga/Reuters
Rebecca Vitsmun/iReport
Madi Alexander
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Library of Congress
TriviaKing/Wikimedia Commons
Jim Castel/CNN
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