With regard to the scanning device that sees through clothes. It does not use Xrays. I don't have time right now to pull the source info. The military also has some very experimental versions that look like binoculars so that people approaching a checkpoint with a handgrenade in their clothes would be spotted before they get to close. It does let you see the human body but not the same as a nude portrait. I am very sure that many people will be very uncomfortable with this technology. Also I am very unsure that this would have caught the explosives in his shoe. First the machine mainly spots variations in densities, but is only sees through relatively light substances. Therefore the shoes outer layer may have come across as normal. I am also unsure that exraying would necessarily caught explosives in shoes. The xray is going to show various consistencies/cavities in a shoe, which with the wide variety of padding etc in some sneakers and shoes, might mean nothing.
I would say that this is a case of someone not associated with a real terrorist cell. From the little we know so far, I would say that someone with very little knowledge of demolitions came up with this stunt. I have only heard that he had detcord and something of C4 consistentcy in the shoe. The det cord by itself would not have set off the explosive if it was C4/semtex style. If this had been planned by Al Qaida or any other major group he would have had something that did not rely on trying to light the explosive with a match. Someone that wanted a simple system with the minimum of metal would use an elctrical detonation system with a PDA as the something that looks like earphones to connect to the shoe.
Again profiling is the best thing that can be done but that is not full proof. It is possible that the reason this person was passed by the french police is because he could not be linked to a terror cell and that would help account for the very amature nature of his explosive. He probably has weak links through mosques with banned groups, but again a terrorist group is not going to want to waste a chance by not having a high probability of success.
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Robert