On the surface, TrueAllele Casework, a computer program that extracts genetic profiles from DNA samples, would seem to mark an advance in criminal justice technology. But defense lawyers say it shouldn't be allowed in court, because Cybergenetics Corp., the firm that owns the program, won't reveal the software's source code, which it considers a trade secret.
The resulting conflict, which is presently playing out in a Pennsylvania murder trial, poses fascinating and important questions: Do we need to know exactly how a given technique works to consider it scientifically reliable and admissible in court? And is it democratically right to convict, and possibly execute, someone based on a secret process the defendant isn't allowed to know?
Start with the science. To oversimplify a bit, ordinary DNA analysis depends on qualitative comparisons made by human beings. Typically, a technician will type a defendant's DNA, then compare it to DNA in samples found at the crime scene. By comparing peaks and valleys in the statistical representation of the DNA sequences, the technician determines the likelihood that the two samples match.