LITTLETON, Colorado -- April 20 marks the anniversary of one of the deadliest school shootings in U.S. history.
RELATED: Columbine shooter's mother talks exclusively to ABC
On April 20, 1999, Eric Harris and Dylan Klebold went on a shooting rampage at Columbine High School in Littleton, Colorado, killing 12 students and one teacher. More than 20 others were wounded.
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The pair made home videos prior to the attack making references to what they were going to do and apologizing to their parents for it.
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Harris and Klebold turned the guns on themselves after carrying out the attack.
More than 100 explosive devices were recovered from the scene.
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