Sources close to the FBI's anthrax investigation say that new genetic information from the spores helped them narrow their search, and that the work allowed scientists to determine the spores were a mixture of different types. But the research has not been made public, and it's unclear how much weight the evidence would carry in court.
The new work is what apparently made investigators confident that the anthrax had come from the Army's biodefense laboratory at Fort Detrick, Md. In 2002, researchers studied the DNA of the anthrax and determined the anthrax used was a strain called Ames. The strain originally came from a cow in Texas and was then sent to a laboratory in Iowa and passed around.
"It's clear that the anthrax ... used in 2001 came from a laboratory," says Richard Lenski, a microbiologist at Michigan State University, who was not involved in the investigation. "And it's a strain that was shared between a number of different laboratories, making it very difficult to sort out exactly which laboratory the strain came form."
So, what to try next?
One idea floating around has been to see if the spores used in the attacks were really all the same. They may have been a mixture, for example, in which 99 percent of the spores were the standard Ames strain mixed with trace amounts of slightly different spores. If there was a mixture of spores in the envelopes, and that mixture was the same as in a vial in a laboratory, that would be interesting.
Lenski says this sort of analysis would have been difficult in 2001 after the attacks, but tools have improved, and this sort of analysis is now possible.
"I don't think there is a name yet for it," he says. "We're very interested in trying it in some laboratory experiments here.
"It's technically very challenging. But again, we don't have the resources that the FBI would have brought to this investigation."
A source briefed on parts of the investigation says the FBI indicated it had matched the anthrax used in the attacks to anthrax at the Army lab in Maryland.
But investigators will have to be careful about saying they've "proved" it came from there.
"The word 'match' is a very dangerous word to use," says Randall Murch, a former deputy director of the FBI laboratory.
Imagine, he says, that the mixture of spores in the attacks is the same as those in a vial at the lab. That's a "match." But for that to really mean something, the best you can do is collect as many samples as you can — from labs, from the wild — and show they do not match.
"That gives you increasing confidence that it came from that laboratory," Murch says. So you can say, with some degree of certainty ... that "this is similar to that."
The technique would be far less convincing than human DNA fingerprinting. If DNA is found at a crime scene, chances are only one person on the planet matches it.
"To my knowledge, bacterial forensics has not been tested in a court of law yet. Not yet," Murch says. "So it would have been a very interesting case had it gone to trial. Because it would have been the first case that I'm aware of where this would have happened."
Federal investigators were looking into what role Army researcher Bruce Ivins played in the 2001 anthrax attacks. An indictment against Ivins was weeks away. The Army scientist apparently took his own life last week.
There's another caveat. Linking the spores to the lab would not necessarily lead investigators to a particular person. A source familiar with parts of the investigation says that in this case, a number of people had access to the supply of anthrax apparently used in the attacks.