THE EXPLOSIVES: Who Built Reid's Shoes?

People who make a living taking bombs apart don't scare easily. But the FBI laboratory experts who dissected Richard Reid's black suede sneakers were horrified by what they found in the soles: bombs that were, as one agent says, "the first of their kind and extraordinarily well concealed."

Each shoe contained about 4 oz. of PETN (pentaerythritol tetranitrate), a powerful explosive produced by the ton for military and construction use. Some was mixed with a plasticizer to produce a substance that resembled putty. More was in short lengths of detonation cord, which looks like a clothes line and is used to cut heavy steel objects like girders. Packed around the PETN was a whitish powder that turned out to be homemade TATP, or triacetone triperoxide. If Reid had succeeded in lighting the fuses sticking out of his soles, the TATP would have blown instantly, setting off the less combustible but more destructive PETN main charge.

"TATP is one of the most sensitive explosives known," says a U.S. government bomb expert. "Drop something on it or rub something against it, and it can go. He was taking a big chance just stomping on it." There is no commercial market for TATP; it's too hard to handle. Terrorists increasingly favor it because recipes are all over the Internet, the ingredients can be found in any pharmacy, it's hard to detect, and mules like Reid are going to die anyway.

Alarmed at the lab reports, FBI director Bob Mueller sent an urgent alert to the FAA, air-security personnel and the law-enforcement community. He ordered agents based in Europe to find out how Reid had acquired the explosives.

The FBI and its European counterparts still don't know who helped Reid, but they are sure that anybody crazy enough to put on those shoes didn't build them himself.

--By Elaine Shannon/Washington