Credit: FILE - In this April 20, 1999 file photo members of a police SWAT march to Columbine High School in Littleton, Colo., as they prepare to do a final search of the school. Classes are canceled Tuesday, April 20, 2010 at Columbine High School on the anniversary of the 1999 shootings. Twelve students and a teacher died in the shootings before two teenage gunmen committed suicide. (AP Photo/Ed Andrieski, File)

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