Siegfried Hecker, sitting in a cold conference room, was asked by his North Korean hosts if he would like to see their "product." "Yes," Dr. Hecker replied. "Do you mean plutonium?" Hecker, former director of the U.S. weapons lab at Los Alamos and familiar with the hazardous properties of plutonium, was surprised when two technicians carried a small red metal box into the room. Inside was a white wooden box containing two glass jars -- they looked like marmalade jars -- one containing a piece of plutonium metal, the other plutonium powder. He later asked if he could hold the...