Federal investigators say they still do not know if anthrax attacks in the United States are domestic or international in origin, and they are appealing for help from the American public.
Top federal officials made a public appeal at the White House Friday for help in tracking down the source of the anthrax by mail attacks that have killed four people and sickened several others.
FBI Director Robert Mueller says investigators have traced three anthrax-laden letters to mailboxes in Trenton, New Jersey. But he says even a $1 million reward for information on the anthrax case has not generated much of a response and investigators are still looking at a wide array of possible sources of the attack.
"It may be well that there is somebody in the United States who is manufacturing the anthrax. As I said, we have not precluded any possibility,' Mr. Mueller said. "We have not said it is domestic, we have not said it is international. We have not precluded any possibility."
As part of the new appeal for public help, Mr. Mueller urged Americans to closely examine the handwriting on the letters containing anthrax that have been widely publicized on television and in newspapers.
"To look at those images and determine if you know who was the writer of those envelopes. And by that, I mean comparing the handwriting on it to any handwriting that you may be able to recognize," he explained.
In the meantime, federal law enforcement officials continue to defend their practice of issuing warnings about the possibility of additional terrorist attacks even though the threats contain virtually no specific information.
The latest example warned of possible attacks soon on some major bridges in California, including the famous Golden Gate bridge in San Francisco.
Attorney General John Ashcroft says he believes it is better to get the general threat warnings out to the public even when there are few specifics.
"We always have to make a judgment about public safety and the degree to which what we say affects public safety," Mr. Ashcroft said, " either by encouraging preparedness or, at the risk of somehow eliciting panic. We try to make a judgment based on two factors - the scope of the threat and the credibility of the threat. And we believe the action we took was appropriate."
One focal point of the anthrax investigation now is the case of a New York woman who died from inhaled anthrax. Officials say the same strain of anthrax that killed hospital worker Kathy Nguyen was present in letters sent to media outlets in New York and to Senator Tom Daschle's office in Washington.
However, investigators say they still do not know how Ms. Nguyen became infected with the anthrax and are now trying to reconstruct her movements in the days before she became ill.