Key dates in the investigation of the anthrax attacks:
October: Anthrax is mailed to lawmakers on Capitol Hill and members of the news media in New York and Florida. By November, five people are dead and 17 others sickened. The victims include postal workers and others who came into contact with the anthrax.
January: Senate office building where anthrax-tainted letters were sent reopens after three months and fumigation. FBI doubles the reward for helping solve the case to $2.5 million.
June: FBI is scrutinizing 20 to 30 scientists who might have had the knowledge and opportunity to send the anthrax letters, a U.S. official says.
August: Law enforcement officials and Attorney General John Ashcroft call Steven J. Hatfill, a biowarfare expert, a "person of interest" in the investigation.
June: FBI drains pond in Frederick, Md., in search of anthrax-related evidence. Frederick is the home of the Army Medical Research Institute of Infectious Diseases, one of the nation's main anthrax research centers. Nothing suspicious is found.
August: Hatfill sues Ashcroft and other government officials, accusing them of using him as a scapegoat and demanding that they clear his name.
December: Postal workers begin moving back into Washington's main mail center, almost two years after anthrax-laced letters killed two employees. The Brentwood facility underwent more than $130 million worth of decontamination and renovation.
February: A white powder determined to be the deadly poison ricin is found in an office of Senate Majority Leader Bill Frist. No one is hurt and no arrests are made.
August: FBI searches homes of Dr. Kenneth M. Berry, who founded a group to train medical staff to respond to biological disasters, as part of anthrax investigation. No charges are filed.
July 11: BioONE, a company founded by former New York City Mayor Rudolph Giuliani, begins fumigating the former headquarters of The Sun, the Florida supermarket tabloid that was the first target in the anthrax attacks.
July 12: Testing determines The Sun's former headquarters is free of anthrax.
July 13: Hatfill sues The New York Times for defamation, claiming the newspaper ruined his reputation after it published a series of columns pointing to him as the culprit.
March 10: Sensor at Pentagon mailroom indicates possible presence of anthrax.
March 14: Alarm at second Pentagon mail facility also sounds possible anthrax presence. Post office in Hamilton, N.J., that handled anthrax-laced letters in 2001 reopens. Further testing determines no anthrax in Pentagon mailrooms.
March 27: The Supreme Court declines to block Hatfill's suit against the Times.
April 11: It's reported that Hatfill's lawyers have questioned at least two journalists and are subpoenaeing other reporters, seeking the identities of their confidential government sources.
Oct. 23: A federal judge orders The New York Times to disclose a columnist's confidential sources as part of a libel lawsuit filed over the newspaper's coverage of the 2001 anthrax attacks.
Dec. 2: The New York Times asks a federal judge to dismiss Hatfill's lawsuit.
Jan. 12: A federal judge dismisses libel lawsuit filed against The New York Times by Hatfill.
Feb. 2: Explaining his ruling, the judge says a New York Times columnist did not act with malice when writing about whether a Hatfill was responsible for the 2001 anthrax attacks.
Aug. 13: A federal judge says five journalists must identify the government officials who leaked them details about Hatfill.