WASHINGTON -- Since the Sept. 11 hijackings, an FBI lab here has been compiling a database of easily concealable knives -- including long, fixed blades hidden in canes, retractable short blades hidden in keys and lipstick tubes, and others made of nonmetal composites that can escape detection by airport magnetometers and X-ray machines. Most of the nearly 90 samples photographed in the extensive database of concealable weapons are commercially available for less than $20, the FBI says. "These knives should be treated as potentially dangerous weapons," warns the "FBI Guide to Concealable Weapons 2003." The booklet, put together by the...