11:10 Harris and Klebold arrive, leaving their cars in the car park outside the cafeteria.

11:14 They leave bags containing 20lbs of explosives in the cafeteria.

11:23 They stand outside the west exit. They pull out shotguns and semi-automatic weapons and begin to fire on students. People start to run and a student makes the first 911 call.

Harris was under psychiatric treatment for anger management and depression before the killing.

11:24 Students in the cafeteria realise what’s happening. Staff try to move them to safe areas. A police patrol car arrives and fires at the suspects.

11:27 Harris and Klebold walk into the school, firing random shots.

11:28 They enter the library, killing 10 and wounding 12 people in the next 7.5 minutes. They fire out of the window at police who have now gathered in the car park. Over the next 40 minutes Harris and Klebold roam the school, firing shots and dropping explosive devices.

2:06pm, the suspects kill themselves in the library. As the authorities are unaware the suspects are both dead, and due to explosive devices planted around the building, it takes the emergency services more than three hours to reach all the survivors and find Harris and Klebold.

* Images from Zero Hour program