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From NPR News, this is ALL THINGS CONSIDERED. I'm Melissa Block. Sources close to the FBI's anthrax investigation say that new genetic information from the spores helped them narrow their search to the Army lab where scientist Bruce Ivins worked. Ivins apparently committed suicide last week. The sources say thanks to this new research, scientists determined that the spores involved were a mixture of different types. The details have not been made public, and it's unclear how much weight the evidence could carry in court.

NPR's David Kestenbaum reports.

DAVID KESTENBAUM: The new work is what apparently made investigators confident the anthrax had come from the Army's biodefense lab at Fort Detrick, Maryland. And it's the result of many years of increasingly sophisticated research. In 2002, researchers studied the DNA of the anthrax and determined the anthrax used was a strain called Ames, originally from a cow in Texas then sent to a lab in Iowa and passed around.

Richard Lenski is a microbiologist at Michigan State University.

RICHARD LENSKI: It's clear that the anthrax that were used in 2001 came from a laboratory. 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 from.

KESTENBAUM: So, what to try next? One idea floating around has been to look and see if the spores used in the attacks were really all the same. Maybe they were actually a mixture. So, say, 99 percent of the spores are the standard Ames strain, but mixed in, hiding in there, are trace amounts of slightly different spores - Some slight genetic variation of the Ames strain that arose through natural mutation as the original sample grew in the lab, maybe different by just a single genetic letter.

If there was a mixture of spores in the envelopes and that mixture was the same as in a vial in a lab, well, that would be interesting. Lenski says this sort of analysis would have been hard back in 2001 after the attacks, but tools have improved, and you can think about doing this sort of analysis now.

LENSKI: I don't think there is a name yet for it. 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.

KESTENBAUM: A source briefed on parts of the investigation says the FBI indicated it had matched the anthrax used in the attack to the anthrax at the Army lab in Maryland. But investigators will have to be careful about saying they've proved it came from there.

Randall Murch used to be the deputy director of the FBI Laboratory.

RANDALL MURCH: And the word match is a very dangerous word to use, okay?

KESTENBAUM: Imagine, he says, the mixture of spores in the attacks is the same as those in a vial at the lab. That's a match. But in order for it to really mean something, you need to know there aren't other matches; that it wasn't passed around other labs. The best you can do is collect as many samples as you can from labs, from the wild, and show they do not match.

MURCH: That gives you increasing confidence that it came from that laboratory. So, what you can say is, with some degree of certainty, okay, you can make a certain statement that in my opinion- in my own opinion in the court of law as an expert witness - in my opinion, that with the analytical techniques I used, this is similar to that, and that's what you're going to say.

KESTENBAUM: The technique would be far less convincing than human DNA finger printing. If DNA is found at a crime scene, chances are there is only one person on the planet who matches it.

MURCH: I'll be honest with you that, you know, there's - to my knowledge, bacterial forensics has not been tested in court of law yet. Not yet. So, it had 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.

KESTENBAUM: And 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.

David Kestenbaum, NPR News.

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