8 Tuesday Morning – April 20th, 1999
Eric Harris and Dylan Klebold arrived at the campus and placed two duffle bags full of propane bombs in the cafeteria. The bombs were set to go off at 11:17 a.m.
There is some question of when the bombs were placed, but researchers have claimed to have footage of the bags being left at 10:58.
Two backpacks containing pipe bombs, aerosol canisters, and small propane bombs were found three miles south of the high school.
These were set to detonate three minutes earlier, possibly a distraction for the police and fire departments. But most of the explosives failed, and only the pipe bombs and aerosol canisters exploded. The resulting fire was contained and quickly extinguished.
At approximately 11:10, Harris and Klebold returned to campus. As Harris pulled into the junior lot, he ran into student Brooks Brown, who, despite recent arguments, warned him to go home immediately.
17-year-old Rachel Scott was having lunch with her friend Richard Castaldo when Klebod threw a pipe bomb in the parking lot that only partially exploded.
Thinking it was just a prank, they paid little attention until Klebold appeared and opened fire. Scott was killed instantly, and Castaldo was shot eight times in the chest, arm, and abdomen. He survived but was left paralyzed below the chest.
Harris and Klebold headed up the west staircase, picking off students at random. Their supposed main focus, the cafeteria, was only briefly entered by Klebold. Harris stayed on the staircase shooting, and officials speculate Klebold checked on the bombs before rejoining him.