The FBI has yet to make any direct connection between the September 11 terrorist attacks and the anthrax letters.

CNN: FBI raids Trenton, N.J., apartment

Hatfill had his apartment searched three times as part of the investigation into who mailed the anthrax letters in fall 2001.

CNN: Researcher says he'll sue over anthrax probe

Investigators say the FBI did not intensify its search for a presumed anthrax letter at the AMI building until 10 months after the first anthrax death because, in part, the FBI was concentrating on its massive search in Washington following anthrax letters discovered there.

CNN: Search is on for anthrax leads at tabloid offices

The officials, linguistic and behavioral experts who have been analyzing the three known anthrax letters, made their assessments more than a month after the first anthrax outbreak in Florida, where no letter was ever recovered -- and at a time of growing congressional frustration over the lack of progress in the investigation.

CNN: FBI profiles anthrax letter writer

Hatfill has twice held news conferences to deny any role in the mailings of anthrax-laced letters last fall.

CNN: Hatfill

Hatfill is one of about 20 to 30 people who have been under scrutiny by the FBI in its investigation of last fall's anthrax-laced letters.

CNN: LSU defends firing Steven Hatfill

Hatfill, who once worked at the nearby U.S. Army biological lab at Fort Detrick, has been called a "person of interest" in the investigation into anthrax-laced letters that were mailed around the nation last year.

CNN: Anthrax agents hunt lab equipment in pond

While Hatfill worked at the government bioweapons lab at Fort Detrick, Maryland, he maintains he never has worked with anthrax and that he was not in New Jersey when the anthrax-laced letters were mailed from there last fall.

CNN: Hatfill

The Maryland facility was designated to screen mail for Congress after letters containing anthrax were sent in 2001 to two senators and media companies.

WSJ: Suspected Poisoned Letter Sent to Senator