11:10 am
Harris and Klebold arrived at the school in separate cars and placed two 20-pound propane bombs in the canteen. They returned to their cars to wait for the explosion, which did not occur.
11:19 am
Two pipe bombs that Klebold and Harris had set up in an open field several blocks away exploded.
Klebold and Harris walked through the halls, shooting randomly. Klebold threw a bomb at the duffel bag bomb in the canteen, which exploded and started a fire.
12:05 - 12:08 pm
Klebold and Harris went to the south side of the library and shot themselves in the head, ending the massacre that had lasted under one hour.