[Mitchell]

Why would Atta attempt to get a federal loan and act like a lunatic in front of her?

Maybe because he was a lunatic? Many a lunatic can't help but act like a lunatic, at least some of the time.

[caa26]

Atta was crazy, but he had to have some deal of control to pull off the whole plot. Most of the highjackers didn't even know they were on a suicide mission, it seems unlikely to me he would blab his intentions to a federal paper pusher.