Originally Posted by TSORon

He brought the C4 back with him from the war, stored it for a couple of weeks in his garage, then took it with him on the flight in question. Most likely he flew back from Afghanistan using a military contract flight, if not an actual military flight, and would not have been screened by the TSA. How he got from his flight termination point to his home is a good question, and may not have involved a commercial flight.