Erroneous early reports said New York was the target of the plot, but that has been denied by both the FBI and by New York Mayor Rudolph Giuliani.
The suspects, to be arraigned later Thursday in Nevada, include a central Ohio man who was given probation after pleading guilty to illegally obtaining bubonic plague bacteria through the mail.
The two were taken into custody late Wednesday in a luxury car outside a doctor's office in Henderson, Nev., a Las Vegas suburb. "The safety of the community was the FBI's top priority throughout the investigation" Bobby Siller, an FBI special agent, said at a Nevada press conference.
"There is no evidence of contamination anywhere in this area as a result of this investigation," he said.
Siller said the FBI acted on a tip about the suspects "from an individual" and had the two men in custody less than 12 hours later. The two were planning to test the substance at an area medical center, Siller said.
The Clark County Detention Center in Las Vegas said 46-year-old Larry Wayne Harris and 47-year-old William Leavitt were in custody on charges of possessing "weapons for mass destruction.".
At a hastily called news conference in New York, Giuliani insisted the current arrest had nothing to do with New York. However, he added, "Any connection to New York might come out in the history or background of one or more of the suspects."
Last year, Harris, of Lancaster, Ohio, pleaded guilty to a count of fraud after he was accused of illegally obtaining bubonic plague bacteria through the mail from a laboratory in 1995. He said he never intended to hurt anyone and was sentenced to 18 months' probation.
"These individuals were involved in the construction of a weapon," said FBI spokesman Aurelio Flores. "We have no idea where they were going to use it."
Flores and Siller said the FBI has secured the area where the car was found and had "made everything safe." Siller said the U.S. Army and the U.S. Air Force assisted the FBI.
In New York, another FBI source had said earlier that the suspects were members of the Aryan Nation, a white supremacist group, and allegedly planned to release a "dangerous bacterial substance" in some city's subways. Flores and Siller said a number of cities may have been discussed.
In Tokyo in 1995, 12 people were killed and another 5,500 were injured when a doomsday cult loosed nerve gas in the subway system.
"These individuals were trying to be maybe copycats of what happened in Japan," Flores said. "They might have talked about different cities." Flores said.
In Washington, a federal law enforcement source said agents were investigating allegations that the two mepossessed anthrax. The source stressed that the tests were not complete and that there have been unfounded instances in the past involving allegations of anthrax.
Siller said the FBI was told the two had anthrax and that initial tests indicated that may be true.
Anthrax is an infectious disease that usually afflicts only animals, especially cattle and sheep. But Anthrax spores can be produced in a dry form suitable for weapons and can be fatal to humans even in microscopic amounts.
The luxury car was taken to Nellis Air Force Base. In statement, base officials said explosive ordnance disposal personnel "were asked to assist FBI agents last night in the Green Valley-Henderson area. Nellis personnel impounded a vehicle on their behalf."
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