Staff file photo by Sam Yu IVINS

Claire Fraser-Liggett, who was speaking Wednesday at a University of Maryland Law School forum on the attacks, also said the work she performed while helping the FBI was based on sound scientific techniques.

"None of the science we used in this was new," she said. "It was applied in a new way and I think we moved the field of microbial forensics forward in a way that we had never expected."

In September and October 2001, Fraser-Liggett, the former president and director of The Institute for Genomic Research in Rockville, was finishing work on the sequencing and analysis of the first genome of a strain of Ames anthrax.

That was a descendant of the same strain used in the 2001 attacks.

"I was at the right place or the wrong place at the time, however you want to look at it," she said. "To bring our expertise to bear was obviously the right thing to do."

Fraser-Liggett, now director of the Institute of Genomic Sciences at the University of Maryland School of Medicine, said the grave implications for the workers became apparent almost immediately, as the FBI required researchers sign nondisclosure agreements that if violated, would result in jail time.

Because of the nature of the life of anthrax spores, which spend most of their time dormant, mutations are relatively infrequent, she said. More than 99 percent of the DNA of anthrax spores are identical. The Ames strain involved in the attacks, which was discovered in a cow in Texas in 1981, left little time for mutations to occur.

Scientists thought this would present an enormous challenge in trying to do any sort of forensics work.

"This would be the equivalent of trying to do DNA forensics on nearly identical twins," she said.

Fraser-Liggett and other researchers obtained their first anthrax sample from the spinal fluid of the first victim, Robert Stevens, a photo editor at a Florida tabloid.

Researchers then compared the sample to their genome for anthrax and discovered four mutations.

They then developed a rapid technique to screen samples with the goal of comparing them to the original Ames genome sequence.

The FBI provided about 120 coded samples, collected from labs in the United States and other countries that stored the Ames strain. Those samples were about 11 percent of the total tested.

According to the FBI, eight of the roughly 1,100 samples could be traced to a single source flask under the control of Bruce Ivins at United States Army Medical Research Institute for Infectious Diseases, Fraser-Liggett said.

"I think that this is where the FBI is really hanging its hat on the validity of the science," she said.

In August, the Justice Department named Ivins as its sole suspect in the mailings. The scientist committed suicide on July 29, just before media reports revealed investigators were preparing to indict him for the mailings.

Ivins' attorney has maintained his client's innocence.

More than 100 people at two labs -- USAMRIID and a lab officials have refused to identify -- had access to the flask. Officials did not explain how they eliminated those other people from their investigation.

On Wednesday, Fraser-Liggett said she believes that since the Ames strain in the flask was composed of so many generations of spores, it had time to develop the four mutations, a question that had lingered until about a month ago.

She said she never believed the science alone would solve the anthrax investigation, and was sorry all of the information would not come to light in a court of law.