I agree, it looks like a sleeper cell..and with the timing of the latest tape (which are morale boosters and congratulatory) and the pickups of the NY and Oregon cells, it fits better. I can't see a motive except "kill americans".
Sac
looks like a sleeper cell..and with the timing of the latest tape Terrorism fits into this scenario more than any other profile I've heard from the so-called experts. It's not some lone gunman from the hills terrorizing the midwest. It's DC - the capital. The tapes you refer to specifally address DC and NY. They want media attention - by doing a night snipe in the DC area he gets live international coverage.
.. and don't forget the attacks on our soldiers in Kuwait.