Investigators could be seen canvassing every house, apartment and business on the route. And officials at the College of New Jersey in neighboring Ewing said FBI agents had been on the campus asking questions about the school's biology department.
Both letters were postmarked at a central mail-sorting facility in Trenton, where the two other infected postal employees worked and may have handled the letters. Authorities also used the postal bar codes printed on the envelopes in their effort to track the letters' routes.
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• N.Y., D.C., Fla. Strains 'Indistinguishable'
Federal authorities disclosed today that testing has revealed that anthrax found in New York, Washington and Florida likely came from the same strain.
"The strains are indistinguishable," said Tom Ridge, director of the Office of Homeland Security, referring to anthrax recovered from a letter sent to NBC News headquarters in Manhattan, a second letter mailed to Senate Majority Leader Tom Daschle's office on Capitol Hill, and at American Media Inc., a tabloid publishing company in Boca Raton, Fla.
The development strongly suggests the three incidents may have been linked.
"It does appear that it may have been from … the same batch," added Ridge. "It may have been distributed to different individuals to infect and descend into different communities."
Officials also said the strains do not appear to have been "weaponized," noting that they are not resistant to antibiotics commonly used to treat anthrax.
Senior law enforcement officials, however, have said the anthrax-laden powder in the letter sent to Daschle was professionally manufactured — highly concentrated and finely milled, making it easy for the spores to become airborne and infect its victims with the often fatal inhalation form of anthrax.
Those qualities require elaborate machinery, suggesting the powder was produced by a well-funded and possibly state-funded operation
Authorities were also probing similarities in the letters sent to Daschle, D-S.D., and NBC anchor Tom Brokaw. They were both postmarked in Trenton, N.J. and mailed in envelopes that had prepaid postage and similar block handwriting on them.
The handwritten letters inside the envelopes were both dated "09-11-01," the date of the terrorist attacks in New York and Washington, and contained within their messages: "Death to America. Death to Israel. Allah is great."
An NBC staffer who opened the anthrax-laced letter mailed to Brokaw contracted cutaneous or skin anthrax and is expected to fully recover.
On Capitol Hill today, officials announced the number of people confirmed to have been exposed to anthrax has dropped from 31 to 28 and that no one there has tested positive for the disease. Those exposed include 20 members of Daschle's staff, six Capitol Police officers and two staffers for Sen. Russ Feingold, D-Wis., whose office is next to Daschle's in the Hart building.
In Florida, an AMI employee who inhaled anthrax spores is continuing to recover after being placed on antibiotic treatment. A fellow employee died of inhalant anthrax earlier this month and six other employees there have tested positive for exposure to the bacteria.