They lied. They said they checked the building twice and found nothing. The camera shows them upstairs for under 3 minutes. There is no way, in the entire 11 minutes they were in the building, they checked it twice, with thermal gear.

They did not do their best, and the video shows them just milling about. They jimmied the lock because they were worried about the fire alarm, but then did not check the building. Not saying schools bares no blame.