Updated

No link has been established between the Sept. 11 hijackings and anthrax attacks that were meant to terrorize the nation, FBI Director Robert Mueller said Wednesday.

Mueller assured the nation's mayors the bureau has assigned unprecedented resources — one of every four employees — to the hijacking and anthrax investigations.

"At this point it is not clear if the few confirmed anthrax exposures were motivated by organized terrorism," Mueller told the U.S. Conference of Mayors. "But these attacks were clearly meant to terrorize a country already on the edge."

The director said more than 7,000 FBI personnel are conducting the investigations.

Three anthrax-tainted letters made public Tuesday included the words "Death to America" and the date "09-11-01" at the top, indicating the anthrax incidents were coordinated.

The Justice Department released copies as it sought help from the public in identifying those responsible for the mail attacks that have killed three people and possibly infected more than a dozen others.

The letters have other similarities suggesting anthrax attacks in New York, Washington and Florida were an organized effort. The strain of anthrax found in two letters and bacteria found at a Florida publishing company were similar. And the three letters were all postmarked from Trenton, N.J.

Letters sent to NBC News anchorman Tom Brokaw and the New York Post appeared identical. Both warned recipients to "Take penacilin now," with penicillin misspelled, and also said, "Death to America," "Death to Israel" and "Allah is Great."

The envelope that contained the New York Post letter was written in the same sort of block letters, slanted to the right, as two envelopes addressed to Brokaw and Senate Majority Leader Tom Daschle, released earlier.

The letter to Daschle contained seven lines written in block letters similar to the other two. "You can not stop us. We have this anthrax. You die now. Are you afraid? Death to America. Death to Israel. Allah is great."

Atop all three notes was the date "09-11-01" in identical handwriting. The envelopes to Brokaw and the newspaper were postmarked Sept. 18. The Daschle letter was postmarked Oct. 9.

Attorney General John Ashcroft said investigators hoped to develop new leads by releasing photographs of the letters and to warn Americans of mail to be wary of.

"All of these ... we hope will alert citizens and others to the kind of thing to look for," said Ashcroft.

Despite the dates on the letters, Ashcroft said authorities can't prove a link to the men who carried out the airliner attacks last month.

Experts in profiling criminals viewed the release of the letters and the identical dates as indications that investigators believe they are dealing with a domestic terrorist capitalizing on the Sept. 11 attacks.

They noted that authorities caught Theodore Kaczynski, the Unabomber, after releasing his 35,000-word "manifesto," which was recognized by Kaczynski's brother.

"The key is access to the bacteria," said Robert K. Ressler, a former FBI criminal profiler.

USA Today reported Wednesday that authorities were trying to determine whether chemicals in the anthrax matched samples of biological weapons stocks from Iraq, the former Soviet Union and other nations. The chemicals help the anthrax spores float in the air and thus become capable of being inhaled. But officials told the newspaper this does not necessarily mean the U.S. attacks were state-sponsored.

Investigators have questioned researchers at labs and universities that may have access to anthrax. They are also questioning labs that have supplies of anthrax available for researchers about who has obtained the bacteria.