Key dates leading up to the 2001 anthrax attacks and the investigation that followed:
Mid-August: Microbiologist Bruce Ivins begins to spend more evenings in his lab at the Army Medical Research Institute of Infectious Diseases, at Fort Detrick, Md. His normal shift was 7:30 a.m. to 4:45 p.m.
Sept. 14-16: Ivins spends three consecutive evening shifts at the lab.
Sept. 17-24: Ivins does not enter the lab.
Sept. 18: The date of postmarks on letters containing anthrax to members of the news media in New York and Florida.
Sept. 26: In an e-mail, Ivins discusses his therapy group and how all of the other people in it are battling depression, sadness and stress. But he's different, he says. "I'm really the only scary one in the group."
Sept. 28-Oct. 5: Ivins works eight consecutive nights in the lab. The total time ranges from 20 minutes to three hours and 42 minutes.
Oct. 5: Robert Stevens, 63, a photo editor at the Sun, a supermarket tabloid published by American Media Inc., dies after inhaling anthrax mailed to AMI's headquarters in Boca Raton, Fla.
Oct. 9: The date of postmarks on letters containing anthrax to Democratic Sens. Tom Daschle and Patrick Leahy in Washington.
Oct. 16: A co-worker of Ivins tells a friend in an e-mail that "Bruce has been an absolute manic basket case the last few days."
Oct. 21: Thomas L. Morris Jr., 55, a postal worker in Washington, dies.
Oct. 22: Joseph P. Curseen Jr., 47, a postal worker in Washington, dies.
Oct. 31: Kathy T. Nguyen, 61, a hospital employee in New York City, dies.
Nov. 21: Ottilie Lundgren, 94, of Oxford, Conn., dies. She apparently inhaled anthrax from her mail.
October to November: At least 22 people contracted anthrax as a result of the mailings. Thirty-one others tested positive for exposure.
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.
February: Ivins does not follow protocol in anthrax samples he submits to the FBI, rendering them unusable.
April: Ivins provides a second set of samples for genetic testing. Both samples were found to have no presence of the anthrax used in the attacks.
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 biowarfare expert Steven J. Hatfill a "person of interest" in the investigation.
June: FBI drains pond in Frederick, Md., in search of anthrax-related evidence. 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.
Dec. 12: An FBI special agent accompanies Ivins to the lab and identifies samples that had not been submitted.
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.
April 7: An FBI special agent seizes additional samples from Ivins' lab.
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.
June 17: One of the samples taken from the Fort Detrick lab tests positive for the four genetic markers common to the anthrax in the attacks.
July 12: Following fumigation, testing determines American Media Inc.'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 31: Investigators ask Ivins about his access to the Fort Detrick lab in 2001. He tells them he went there "to escape" his home life. A review determines that Ivins' role in experiments does not justify the time he spent in the lab in 2001. Investigators ask Ivins to explain the differences in samples he submitted to the FBI in 2002 and those an investigator seized in April 2004.
March 27: The Supreme Court declines to block Hatfill's suit against the Times.
Oct. 23: A federal judge orders the 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 Times asks a federal judge to dismiss Hatfill's lawsuit.
Jan. 12: A federal judge dismisses libel lawsuit filed against the Times by Hatfill.
May 7: Ivins tells investigators that, within three months after the attacks, he had been told by co-workers that anthrax samples in his lab were similiar to the anthrax used in the attacks. Investigators interviewed the co-workers, who deny disclosing such information to Ivins.
Aug. 13: A federal judge says five journalists must identify the government officials who leaked them details about Hatfill.
Nov. 2. Authorities search Ivins' home, taking 22 swabs of vacuum filters and radiators and seizing dozens of items.
March 7: Federal judge holds a former USA Today reporter in contempt and orders her to pay up to $5,000 a day if she refuses to identify her sources for stories about Hatfill.
March 11: Federal appeals court blocks the fines.
June 27: Federal government awards Hatfill $5.8 million to settle his violation of privacy lawsuit against the Justice Department.
July 29: Ivins, 62, dies of an apparent suicide after being informed by the FBI that charges were likely to be brought against him in connection with the 2001 anthrax attacks.
Aug. 6: FBI briefs families of victims and releases documents about investigation of Ivins.