Saturday will mark 25 years since the shooting at Columbine High School in Littleton, Colorado. Twelve students and one teacher were killed when a pair of students opened fire during a school day. Author Dave Cullen wrote the book Columbine which details the events and stories behind that tragic day and he spoke with CBS News Streaming.

<p>Saturday will mark 25 years since the shooting at Columbine High School in Littleton, Colorado. Twelve students and one teacher were killed when a pair of students opened fire during a school day. Author Dave Cullen wrote the book Columbine which details the events and stories behind that tragic day and he spoke with CBS News Streaming.</p>

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