Wed March 9, 2011
Research News

Lab Vs. Courtroom: Different Definitions Of Proof

A research study published this week offers a powerful reminder of the difficulty of using cutting-edge science in the courtroom.

The study, reported in the latest issue of the journal Proceedings of the National Academy of Sciences, describes the genetic fingerprinting technique that the FBI relied on in its investigation of the 2001 anthrax letter attacks.

In 2008, the Justice Department was poised to indict a researcher named Bruce Ivins for committing the crime, but Ivins took his own life. A key piece of evidence tying Ivins to the anthrax attacks was a genetic match the FBI made between the anthrax bacteria in his lab and the bacterial spores found in the letters.

Fingerprinting Anthrax

To understand how the FBI made that connection between letters and lab, you have to know something about how the anthrax bacteria grow in the laboratory: "They go from one cell to nearly a billion cells overnight," says Paul Keim, a geneticist at Northern Arizona University and TGen, a nonprofit biomedical research foundation.

Those billion cells are what microbiologists call a colony. "It's a group of bacterial cells that have grown up from a single cell," says Keim.

If every batch of bacteria produced identical colonies, there would be no way to tell them apart. But it turns out each batch produced some colonies that looked slightly different from one another.

Scientists working with the FBI looked at the genomes of these different colonies, "and what they found was there were subtle differences in their genome that affected they way they grew on a plate," says Keim. Those differences gave a kind of genetic fingerprint for each batch of anthrax.

A Genetic Signature? Yes. But Is It Unique?

The FBI had a repository of 1,000 batches of anthrax bacteria from various labs, and the new fingerprinting technique, let the FBI ask a crucial question: "Is the DNA fingerprint that they saw in the letter spores [also found] in any of these repository samples?" says Keim. "And they found them."

In fact, all the bacterial samples in the letters matched the fingerprints of samples taken from Ivins' lab.

That sounds pretty conclusive, but here's the problem: Keim says scientists don't yet know if the letter samples might match other batches as well. It's not certain that each batch has a distinctive signature.

"We're going to go and look," he says. "We're going to go look and see if there is, in fact, a unique genetic signature in every single batch. Theory says there should be."

Science Ready For The Courtroom?

Testing theories is what science is all about. But how rock solid does a theory have to be before you can use it in the courtroom? Stanford Medical School's David Relman was vice chairman of a National Academy of Sciences panel that looked at the science the FBI used in its investigation.

"There's always a tension between wanting to embrace and integrate a new approach quickly and yet wanting to be sure that it's done properly, and properly validated," says Relman.

Another problem the academy panel wrestled with is how a jury responds to scientific evidence.

"One of the things that concerns me when science meets law enforcement is that science is sometimes put up on a pedestal that's a bit higher than other pieces of evidence," says Alice Gast, president of Lehigh University and chairwoman of the panel. She worries that calling something scientific makes it sound more definitive than it really is.

The FBI says science was only one part of its case against Ivins, but it clearly was an important part — and weighing scientific evidence is tricky for scientists, let alone members of a jury. Copyright 2011 National Public Radio. To see more, visit http://www.npr.org/.