The Columbine Attack
Eric Harris and Dylan Klebold planned Columbine primarily as a bombing. The timers were set to begin with the eruption of two big propane bombs in the cafeteria at 11:17 a.m. That was the start of "A" lunch, the maximum human density anytime, anywhere in the school on any given day. Maximum body count.
Eric and Dylan then intended to open fire at fleeing survivors (guns here). They also loaded their cars with bombs and gasoline, set to detonate about noon.
These are the official Jeffco sheriff's photos of the big bombs. All failed. (Only the pipe bombs worked. The "diversion" bomb in a field ignited its detonator and started a grass fire, but also failed to explode.)
Explanations appear below the photos.
Screen print from the bomb summary pages of the JeffCo Sheriff's Department's official report. Read more here.
Another screen print from the bomb summary pages of the JeffCo Sheriff's report. These are a great intro.
One of the two big propane bombs in the cafeteria. The timing device is to the left. (This is how it was found. Its duffel bag was burned away by the Molotov Cocktail Dylan Klebold threw at it trying to set it off, late in the attack. Eric Harris also fired at it with his rifle.)
The second big propane bomb in the cafeteria. You can see the gasoline can as part of the bomb. The mess left during the panic is also captured well here. (The yellow cards are evidence markers, added by Jeffco.)
Timing device from one of the cars, employing a 9V Duracell battery, set to noon.
One of Eric Harris's pipe bombs, lodged in a wall, with evidence marker.
This slide and the following show the car bomb explosives, at various stages of disassembly by Jeffco. (Eric Harris and Dylan Klebold didn't bother to rig everything together. The main device in each car was supposed to set it off and erupt the big jugs of gasoline, etc.)