Explosion at Boston Marathon ... was there a planned drill or wasn't there?

I just found out about the "Terrorist Attack" from Whatreallyhappened.com, and then parroted what they said at NaturalNews.com:

What's not yet being reported by the mainstream media is that a "controlled explosion" was under way on the same day as the marathon explosion.

As the Boston Globe tweeted today, "Officials: There will be a controlled explosion opposite the library within one minute as part of bomb squad activities."

Bloomberg news is now saying, "This is very likely a terrorist attack."

The question is: Who are the terrorists? It's far too early to take an informed guess on all this. However, it is indisputable that the FBI is actively engaged in carrying out bomb plots in the United States, then halting them at the last minute to "catch the terrorists." This fact has been covered by the New York Times, among other publications.

But now it turns out that tweet came after the "terrorist attack," so the controlled explosion doesn't seem to be a drill at all, but a means to destroy an already existing bomb. Sorry for jumping the gun like that! I'll try to keep on this, but the library's going to be closing pretty soon and I'll have to go home, losing access to this computer.