Columbine by Dave Cullen:
Just after noon, a SWAT team made its first approach on the school. The officers commandeered a fire truck for cover. One man drove the truck slowly toward the building, while a dozen more moved alongside. Near the entrance, they split in half: six and six. Lieutenant Terry Manwaring’s team held back to lay down suppressive fire and later work its way to another entrance. At approximately 12:06, the other six charged inside. Additional SWAT team members arrived moments later and followed them.
The team thought they were in striking distance of the cafeteria. They were on the opposite end of the building. Lieutenant Manwaring had been inside Columbine many times, but he was unaware it had been remodeled and the cafeteria moved. He was perplexed.