Is being afraid of foreign terrorists easier than home grown crazies?

Timothy McVeigh, the D.C. Sniper, countless school shootings in the last 10 years. But thinking about these things isn't nearly as scary as the threat of terrorists, although they happen all over America. Is the next big attack going to come from terrorism, or will it be one of our own that inspires destruction? Should be be more wary of our own citizens?