WASHINGTON (AP) _ Despite an intensive monthlong investigation, the Bush administration has not been able to determine whether deadly anthrax attacks were the work of domestic criminals or overseas terrorists, Homeland Security Director Tom Ridge said Wednesday.
``I am hopeful, like the rest of America, that the anthrax has stopped permanently,'' he said at a White House news conference, but he did not say he believed that was the case.
Ridge spoke as investigators worked to pierce the mystery surrounding the death last week of Kathy L. Nguyen, a New York woman who contracted inhaled anthrax. Her case is the only one that hasn't been linked to the postal service.
Investigators are tracing Nguyen's steps to see where she could have encountered the deadly germs, including using subway computer records to track how she moved about the city. Quiet federal monitoring of subway workers ``for quite some time now'' shows no evidence of anthrax exposure in the subway system, Dr. Jeffrey Koplan, director of the Centers for Disease Control and Prevention, revealed Wednesday.
Anthrax, linked to three letters thus far, has killed four Americans and sickened 13 more by the CDC's count. Four postal facilities remain closed.
``We don't know its origin,'' Ridge said of the deadly bacterium.
``We have not ruled out whether this was an act of an individual or a collective act, whether it was a domestic source or a foreign source. Hopefully one of these days we'll be able to answer both questions. Today we are not.''
He also disclosed that authorities had received roughly 10,000 anthrax hoaxes, and that 25 people had been arrested as a result. ``Obviously, the postal inspectors and Department of Justice will move as aggressively as possible'' to bring to them to justice, he said.
Eight days after the last anthrax diagnosis, a top federal health official said the worst of the anthrax-by-mail episode may be over. ``For this episode, we're out of the woods,'' said Dr. Anthony Fauci of the National Institutes of Health.
The big fear had been that the New York woman was the first victim of an anthrax attack by some means other than mail, but ``every day that goes by without seeing another unexplained inhalational case makes it less and less likely'' that happened, said Fauci.
But another attack _ either newly mailed anthrax-tainted letters or by some other means _ can't be ruled out. Particularly until the death of Nguyen is solved, ``vigilance is heightened around the country,'' said the CDC's Dr. James Hughes.
Nguyen last week became the fourth person to die from inhaled anthrax in the outbreak that began with the September mailing of tainted letters to news media in Florida and New York, and to Senate Majority Leader Tom Daschle.
Those letters are presumed to have left a trail of contamination in post offices and government buildings along the East Coast _ but traces have been found in the Midwest and as far away as Russia, in a diplomatic mailbag sent to a U.S. consulate.
The Postal Service raised to $1.25 million its reward for information leading to the arrest of whomever is responsible for the anthrax-by-mail attacks. The advertising company Advo chipped in $250,000, Postmaster General John E. Potter announced.
Concern that anthrax was being spread overseas eased on Wednesday when White House spokesman Ari Fleischer said a suspicious letter mailed to the U.S. consulate in Lahore, Pakistan, was free of spores. Preliminary tests had detected the bacteria in a substance inside the letter.
Officials in New York were using a number of methods to try to track Nguyen's last moments, including tracing a computer-coded prepaid ticket she used in the city's bus and subway system. The system records the time and place a ticketholder used the system. Nguyen used the subway to commute from her home in the Bronx to her workplace in the stockroom at Manhattan Eye, Ear and Throat Hospital.
``The key to this investigation ... is just knowing where she was,'' Koplan said, calling it vital that anyone who recognizes Nguyen from posters plastered around New York contact investigators with even the smallest tip. ``I am struck at how difficult it is to get the kind of detailed information we need on day-to-day, hour-to-hour activities.''
In Washington, thousands of pounds of mail addressed to government agencies have been piling up since Daschle's letter was opened Oct. 15. The Postal Service said Tuesday it had begun sanitizing this mail and would start delivering it within 24 to 48 hours. Two facilities, in Bridgeport, N.J., and Lima, Ohio, are cleansing about 750,000 pieces of mail a day by irradiating it.
But getting back to normal on Capitol Hill will take at least several more weeks.
Still facing cleanup is the Hart Senate Office Building where Daschle's office is located. Officials on Tuesday abandoned plans to pump chlorine dioxide gas into the entire building amid fears it may damage computers and artwork without killing all the bacteria. The latest plans are to try gassing just the offices where most of the potent anthrax spread, and do more traditional cleanup in the rest of the building, which won't reopen before Nov. 21.
Regulators are furiously trying to stem fraud arising from the public panic over the anthrax crisis.
The Securities and Exchange Commission suspended stock trading of a company that claimed it is developing an anthrax disinfectant, warning investors Tuesday to be wary of unproved bioterrorism claims. And the Federal Trade Commission disclosed it is investigating hundreds of Web sites that sell potentially illegal antibiotics, fake anthrax and smallpox remedies and fake at-home anthrax tests.