April 20, 1999, was an ordinary school day for students at Columbine High School in Littleton, Colorado. Classrooms were full of students finishing their last assignments before final exams. When the bell rang for the first lunch period, some went outside to enjoy the warm weather, but minutes later, the sound of gunfire pierced the peaceful spring day. At 11:19 A.M., two students, Eric Harris and Dyland Klebold, unleashed a long-planned murderous...