You have a very short memory. Is 9/11 not enough reason to start deporting Moslems in serious numbers? Not the Cole? Not the embassy bombings? Not the LAX shooting? Not the shooting of the Marine in Kuwait? Not the bombing of the French oil tanker, nor the earlier likely sabotage at a fertilizer plant in Toulouse? Not the bombing in Bali? It that not warning enough? We have to wait until we convict one or more Moslems of this sniper attack, and attacks outside our borders don't count?
The POINT of deporting as many Moslems as possible is to prevent these kinds of attacks by reducing the supply of terrorists and their support networks. Prevent. Not respond to. PREVENT.
Think about how we can PREVENT or reduce the impact of the next attack. Oh no! By your reasoning, we should just wait.
Oh, and to anticipate your response, the Amish have not been active terrorists overseas, either.