The temporary shutdown of much-needed lab space at the U.S. Army Medical Research Institute of Infectious Diseases marks a notable return of investigators to the Frederick facility where numerous employees were questioned by the FBI in the early months of the investigation. In recent months, FBI agents have seized medical records and computer hard drives from the institute, causing friction with Fort Detrick officials, according to a source in contact with the Army institute's scientists.
Neither the FBI nor the Army would describe the work being done since the labs were closed Friday. But a law enforcement official and a scientist said it has not produced a major breakthrough in the case.
Debra Weierman, a spokeswoman for the FBI's Washington field office, said agents would be at the labs "for a few more days."
Investigators have shut off access to bacteriology labs in the main USAMRIID building and an adjoining building where anthrax research is done or has been done, according to the source. Only caretakers responsible for feeding research animals are being permitted to enter, the source said.
Outside scientists said the agents might be hunting for stray spores of anthrax that match the genetic and chemical signature of the anthrax mailed in September and October 2001. The FBI has said in court papers that it has engaged 19 labs to study the spores in order to trace them back to a particular facility.
Investigators have found that the mailed anthrax consists of a combination of two different samples that form slightly different patterns when the bacteria are grown in the lab, The Sun reported this month. Scientists can use this peculiarity in combination with the genetic fingerprint of the anthrax, isotopes in the water used to grow it and the properties of chemical additives to try to match the powder to its source.
Henry L. Niman, a Pittsburgh molecular biologist who has followed the anthrax case closely, noted that spores of anthrax can survive for centuries in soil, and that spores might linger in a laboratory for years after research was performed there.
"My guess is they'd be vacuuming in all the corners, hoping to find spores that match," Niman said. "If they can show it came from a certain lab, then they can see who had access to that lab."
A possible complication if a match is found at USAMRIID is that its laboratories were used extensively after the anthrax mailings to study the envelopes and their contents. So if matching spores are found, it might be difficult to prove whether they were there before the mailings or spilled during a subsequent examination of the evidence.
The anthrax killed five people, including two Washington, D.C., postal workers, and sickened at least 17 others, leading to the shutdown of numerous government buildings.
Because the accompanying notes included militant Islamist rhetoric and were mailed in the weeks after the Sept. 11 attacks, investigators at first pursued the possibility that al-Qaida might be responsible.
But the notes also warned that the letters contained anthrax and urged recipients to take antibiotics, which investigators believe points to an American more intent on sounding an alarm about bioterrorism than killing large numbers of people.
Since late 2001, the investigation has appeared to focus chiefly on American biodefense laboratories, including USAMRIID, which first identified the Ames strain of anthrax used in the letters and was its main distributor.
Last August, Hatfill sued the FBI and Justice Department, alleging that they had wrongly targeted him as the anthrax mailer. The lawsuit has been put on hold until at least October, after the FBI told the judge that it might interfere with the investigation.
This month, Hatfill filed a second lawsuit against the New York Times and one of its columnists, Nicholas D. Kristof, claiming Kristof's columns implied he was the perpetrator.