The Limits of Forensic Microbiology, or "We prosecute people, not beakers"

The FBI and major media have placed a lot of emphasis on the techniques used to identify the specific batch of Ames anthrax used in the Daschle/Leahy letters. Careful consideration of these methods is certainly important, for their accuracy is critical to the FBI's theory of the case.

However, at the end of the day, the forensics are only one piece of evidence. Much as we may desire a tidy resolution to the case, the forensics simply do not have the power to provide it. They can identify a batch, or a pooled sample, and one or more flasks. But they can never tell you who obtained anthrax from the flasks. The strains found in Ivins' flask had been shared; 100 people had access; and who knows how many more had access to the samples maintained by these 100 people?

At the end of the day, it will be the detective work that solves the crime.

As an article in the August 20 NY Times points out:

The scientists say they are confident the F.B.I. has identified the source of the anthrax, a flask in the custody of Bruce E. Ivins, whom the F.B.I. considers to have been the perpetrator of the attacks. But almost a hundred other people were known to have had access to cultures from the flask, and the scientists say they have no opinion as to whether Dr. Ivins, who committed suicide last month, was the culprit.

And the Nature editorial makes the same point:

... The genetic analysis itself seems quite solid. The FBI has collaborated with some of the best outside scientists on anthrax, and on 18 August convened many of them to answer journalists' questions about the science. The researchers on the panel explained that none of the analysis techniques used in this case is new; just the application to anthrax forensics. Several peer-reviewed papers on the forensic work have already been published, and another dozen or so are anticipated.

Although this openness about the techniques is commendable, neither the conclusions drawn from the scientific analysis, nor such crucial legal elements as the veracity of the provenance and handling of samples, have been tested in court. So far only one side of the story has been heard: that of the prosecution...

The FBI should explain why it thinks the scientific evidence implicates Ivins himself, and not just the flask. As Kemp aptly puts it: "In this country, we prosecute people, not beakers."

I much prefer that analogy to the one about the spore on the grassy knoll. Let's get clear about what the scientific evidence does and does not indicate.

How did the FBI get from the beaker to Ivins?