On 9/11 more than 45 drills were under way. One of them took place in New York as FEMA arrived the day before the attacks to do an anti terror drill.
In every major “terrorist” or mass shooting event since then a drill was on the way before or on the day at the same time suggesting that if one is about to take place where you live it might be a good idea to move out for the day.
This happened with Sandy hook, 7/7 London Bombings and in Wahington DC recently and in Boston to name a few. In fact as many as 63 drill went live accidentally according to this list. In the last hour or so another mass shooting was reported at the Capitol building, Washington and guess what! Yep you got it in one: A drill was taking place! (article published on the 24th 2013 indicating that the drill would take place from September through to Oktober 3th of that year)
Now call me a conspiracy nutter but with the US Government shut down and Obama and his banking mates in a panic and the gun grab stalling and the general public not buying the second massive IRS called Obama care and the war efforts stalling what could be more convenient than an attack on the government buildings itself?