'More questions than answers' in Fed anthrax case

WASHINGTON (CNN) -- A spokesman for the U.S. Postal Inspectors said Friday he has few answers about a preliminary test that found anthrax in a mail bin at a Federal Reserve sorting facility.

Dan Mihalko said further testing is being done to double-check the findings of the preliminary test. Meanwhile, investigators are trying to track the source of the apparent mail bin exposure, including determining whether the results came from the bin itself or from letters, and where the mail in question had been before arriving at the Fed, he said.

"Right now, even I have more questions than answers," Mihalko told CNN.

Five people have died from inhalation anthrax since early October, when anonymous anthrax-laden letters were sent to several media outlets and U.S. congressional leaders. Authorities believe the letters may have been sent by the same person. Six other people also contracted inhalation anthrax but survived, while at least seven others contracted a milder skin form of the disease.

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Tests on the 100 to 150 letters that were in the Federal Reserve bin are expected to continue over the weekend, said Federal Reserve spokeswoman Michelle Smith. So far no letter has shown any sign of anthrax, she said.

The sorting facility is in a processing facility set up in a courtyard outside the Reserve building. The Fed said tests on both the inside and outside the Federal Reserve building so far have been negative.

Although the preliminary tests on the bin came back positive Thursday, Mihalko cautioned that all mail sent to U.S. government agencies in Washington since the anthrax attacks began is irradiated before delivery, and irradiated mail can show positive field test results.

"You see so many false positives," he said. "We may see things change."

The Fed's environmental testing contractor, Applied Environmental, opens each piece of mail and swabs it for anthrax exposure before sending it into the building, Smith said. The company is conducting additional tests in an effort to single out the source of the anthrax exposure found Thursday, she said.

Three Federal Reserve employees and three contractors process mail at the facility in safety suits to avoid direct contact with incoming mail.

Federal Reserve Chairman Alan Greenspan and board members were notified about the discovery late Thursday.

As a precaution, the board postponed Friday's planned meeting at the Federal Reserve building.

-- CNN National Correspondent Susan Candiotti contributed to this report.