Anthrax timeline:Late September, 2001
Envelopes containing threatening letters and a grainy brown substance arrive in the offices of ABC, CBS, NBC, and the New York Post.
October 5th, 2001
Robert Stevens, a photo editor for the Florida-based tabloid "The Sun," dies of inhaled, pulmonary anthrax after opening an anthrax letter sent to the paper's office in Boca Raton. He was 63.
October 15th, 2001
A threatening letter containing a purer form of anthrax spores arrive in the offices of Senator Tom Daschle, D-S.D. — a similar letter destined for the office of Senator Patrick Leahy, D-Vt., is incorrectly routed to the State Department mail center.
Late October, 2001
Government mail service is shut down; 31 workers in the Capitol test positive for the presence of anthrax, although most are not actually infected. Two Postal Service employees die of anthrax inhalation. The House of Representatives temporarily closes in response, and Homeland Security head Tom Ridge wonders if this second round of letters could be said to contain "weaponized" anthrax.
A second wave
President Bush calls the anthrax letters "a second wave of terrorist attacks upon our country." The USPS begins irradiating mail destined for government offices in particular Washington, D.C., zip codes. A 94-year-old, Ottilie Lundgren, is the fifth and final person to die of anthrax.
President Bush says that investigators still aren't certain where the anthrax came from. DNA testing shows that both sets of letters used anthrax from a single strain of the disease — the "Ames" strain — which has been used for vaccine testing in U.S. labs for years.
Who had the ability?
The FBI says they are looking at some 20 scientists who could have had the access and means to produce the mailed anthrax.
Stephen Hatfill: a "person of interest"
The FBI says that biowarfare expert Stephen J. Hatfill is a "person of interest" in the investigation.
Hatfill sues Attorney General John Ashcroft and the Department of Justice for libel, saying they are ruining his good name as a scientist.
Government settles with Hatfill
In June, 2008, the Justice Department settles with Hatfill, agreeing to pay him US $5.82 million.
Bruce Ivins: investigation and suicide
After an 18-month investigation, the FBI informs scientist Bruce E. Ivins, 62, that he is likely to be charged in connection with the 2001 letters. Ivins worked at the same biodefense center as Hatfill, and had been working for years on a more-effective anthrax vaccine. In an apparent suicide, Ivins takes an overdose of Tylenol with codeine. His therapist said Ivins' state of mind had worsened in past weeks, and that she was scared of him. His defense attorneys say Ivins was innocent and under extreme pressure as a result of the investigation.
Sources: the New York Times, the Washington Post, and the LA Times.