Federal authorities are now convinced the anthrax mailed in poison letters was made in the United States, and told ABC News they are investigating a former anthrax researcher who allegedly threatened to use the potentially deadly bacteria.

        Unknown to all but a few government officials, the United States has been producing small quantities of weapons-grade anthrax for several years at two secret locations, one of them the Army's Dugway Proving Ground in the Utah desert.

        The FBI is now interviewing current and former scientists in Utah and at the second secret anthrax-producing facility, Battelle in Columbus, Ohio, a nonprofit corporation that does the work for the CIA and the military.

        An estimated 200 U.S. scientists dealt with the anthrax program over the last five years, and federal authorities have told ABC News they are now investigating the activities of a senior research scientist who FBI sources say was twice fired from Battelle and who allegedly made a threat to use anthrax in the days after Sept. 11.

        According to an FBI affidavit, agents searched the home of one former top Battelle scientist in late September after he allegedly made threats. Agents said they found suspicious chemicals but no anthrax, according to the sources.

        The scientist confirmed to ABC News that agents had searched his home and taken his personal computer, but he denied any involvement in the attacks. He also insisted he had quit his post at Battelle and was not fired.

Battelle research aids the ailing, military

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