Members of the Threat Assessment Group (TAG) attempt to determine the factors that lead to the Columbine High School shootings.

Peter Jennings and other correspondents cover the unfolding events in Littleton, Colorado, as two students over a period of four hours, murdered 13 people and wounded another 33 with gunfire and pipebombs before taking their own lives. The motives of Eric Harris and Dylan Klebold remain a mystery, although investigators have formed theories based on what was found in the killers' home and on their personal computers. Includes an address to the nation...