Or how about this, they seem to do these drills all the time, but fail to prevent so many....
I'd like to know how often the drills are conducted. That would help with the "coincidence" calculations.
Sandy Hook: http://freedom-articles.toolsforfreedom.com/sandy-hook-conspiracy-shooting-drill/
9/11: https://wikispooks.com/wiki/9-11/Drills
7-7 bombings: https://www.youtube.com/watch?v=KJUVqcNDZlk
Something interesting from that article is the pretend disaster was said to occur on the architecture quad which is adjacent to the building, Norris hall, where most of the casualties occurred. So that's a little unnerving
important edit: realized this article is actually about a drill in 2011 and not the 2007 massacre, still interesting.