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The anthrax (search) false alarm this week served as a reminder that federal authorities still haven't caught whoever was responsible for the all-too-real attacks in 2001 that left five people dead.

No arrests have been made and no charges filed in the case the FBI has dubbed Amerithrax. Attorneys and scientists who have followed the investigation — and at times been touched by it — say they see no evidence of recent activity.

Debra Weierman, spokeswoman for the FBI's Washington field office, disputed that. She said 30 FBI agents and 15 postal inspectors are assigned to the anthrax probe, and more than 5,000 grand jury subpoenas have been issued.

"The investigation remains intensely active," Weierman said.

Dr. Steven J. Hatfill (search), the one person identified by former Attorney General John Ashcroft as a "person of interest" in the case, has filed suit against Ashcroft and the government, asserting they ruined his reputation. Hatfill has said repeatedly that he had nothing to do with the anthrax-tainted letters that scared a jittery nation a month after the Sept. 11 attacks.

The FBI's dogged surveillance of Hatfill has all but ended. Aides to Attorney General Alberto Gonzales (search) refused to comment when asked whether Hatfill remains of interest to investigators.

Hatfill, 51, reportedly has been unable to find work. His attorney, Thomas Connolly, would neither agree to be interviewed nor make Hatfill available for this story.

U.S. District Judge Reggie Walton, who is overseeing Hatfill's civil lawsuit, provided a concise summary of the investigation at a court hearing in October. Walton criticized federal officials for leaked information that cast suspicion on Hatfill and said he doubted the FBI was close to solving the case.

"It doesn't seem to me there's a significant likelihood of anything in the near future that's going to change the status quo," Walton said after reading a sealed affidavit from the FBI agent who is in charge of the investigation.

The anthrax letters, bearing postmarks from Trenton, N.J., began surfacing in October 2001 at media outlets in New York and Florida, and in senators' offices on Capitol Hill. By November, five people had died — a photo editor for the tabloid newspaper The Sun, two postal workers who were infected at a Washington mail-handling center and two women who had no known connection to any of the recipients but who may have come into contact with contaminated mail.

Investigators quickly focused on 20 to 30 scientists with the training and experience to handle anthrax and turn it into a deadly weapon. Authorities took a particular interest in the U.S. Army Medical Research Institute of Infectious Diseases at Fort Detrick in Frederick, Md., which housed the strain of anthrax found in the mail.

Hatfill was once a researcher at Fort Detrick (search). The FBI twice searched Hatfill's apartment near the lab. Agents drained a pond outside Frederick in 2003, hoping to find discarded evidence. They didn't.

Last year, they interviewed employees at the Fort Detrick lab, asking about access to sensitive areas where scientists work on anthrax and other biological agents, said Rosemary McDermott, the lawyer for the employees.

Another McDermott client, former lab employee Ayaad Assaad (search), also talked to the FBI for at least a second time.

Assaad, who now works for the federal Environmental Protection Agency, said the agents quizzed him about his knowledge of producing finely powdered anthrax like that used in the letters.

They assured Assaad he is not a suspect in the attacks, both Assaad and his lawyer said.

Assaad is an expert on the toxin ricin (search) and says he has never worked with anthrax. He said he gave the FBI receipts and other materials showing he was in the Washington area during periods in September and October 2001 when the letters might have been mailed from New Jersey.

An anonymous letter sent to the FBI after the first anthrax letters were mailed but before anyone turned up ill. were known warned that Assaad might be planning a biological attack. Investigators believe it is more likely the anthrax mailer sought to frame Assaad for the crime.

Since that round of questioning, "all has been quiet," McDermott said.

In August, authorities searched the homes of Dr. Kenneth M. Berry of New York as part of the anthrax investigation. Berry founded an organization that trains medical professionals to respond to chemical and biological attacks. No charges were filed.