Reid may have been an incompetent idiot, but that's not all he was. He was an incompetent idiot who was 6' 4" -- and who thus presumably had large feet -- and who had a British passport. Thus he had useful qualities as far as al Qaeda was concerned, and they made use of them. No wonder, as was reported in one of today's stories, bin Laden went to the trouble of meeting Reid when he was in an al Qaeda training camp in Afghanistan.
I hadn't seen this thread until today. I saw a report in the German newsmagazine Focus today about the phone calls between Reid and Moussaoui being intercepted, so I did a search before posting the Focus story. I see this thread was already up here.
The Focus article also mentiones that this guy was using the same explosives as used with the Lockerbie bombing and that the detonator did not contain metal.