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.
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.