Originally Posted by Bart

Actually, terrorists are also amateurs. Yeah, hard to believe, but it's true. The planners, organizers, fund-raisers and bomb-makers are the professionals. But the person who actually carries out the attack is usually an amateur who has received training but has very limited operational experience. And, depending on the motivation, this person may exhibit even more suspicious behavior than even the drug smuggler.

Even so, even professionals have a hard time concealing their behavior. They all have a "tell."