Federal investigators have almost zilch in the way of clues to identify the so called "unabomber" and are relying completely on help from the public, a source tells TIME San Francisco bureau chief David S. Jackson. Since the mailbomb killing Sunday of a Madison Ave. executive in North Caldwell, N.J., investigators from the FBI, the Bureau of Alcohol, Tobacco and Firearms (ATF), and the Postal Service have received about 500 calls with tips on the bomber, an ATF source told Jackson. "It takes time tracking them down, but they are still appealing to the public to call in with tips," says Jackson. "They have no clues." Two they have: the San Francisco postmark and the initials "FC" on pieces of most of the 15 bombs deployed over the last 16 years. The feds' tip line: 800-701-BOMB.Post your opinion on theCrimebulletin board.