Um, I have this Crazy crackpot theory. No, I don't think it was our own government, and that's pretty stupid I think. But it wouldn't surprise me if they might have possibly did some sort of emergency demolishing. Not, because they wanted to, but because it may have leaned over, and taken out several more buildings, and could have claimed a lot more lives. Please excuse the crappyness, its just so I could do it quick.
Basically, it shouldn't fall straight down, it would have more likely, fell over from the top.