COLUMBINE: 12 years later

Two heavily armed teenage gunmen injured 24 other students before killing themselves April 20, 1999.

The two people who engineered their hometown's infamy were Dylan Klebold, 17, and Eric Harris, 18. They are perhaps two of the most talked about teenagers in recent history, their names and faces stamped in the annals of American crime forever.

What made these two young men, who seemed to have no outwardly threatening, overtly violent tendencies, arm themselves to the teeth and blow away twelve classmates and a teacher, before each taking a bullet themselves? To understand what went on before the Columbine High School shooting, we must look at what went on that Tuesday - and what went on before.