DNA Under the Scope, and a Forensic Tool Under a Cloud

Marina Stajic worked for nearly three decades as director of the forensic toxicology lab at the medical examiner’s office in New York City. Last week Dr.. Stajic, 66, filed a lawsuit against the city, claiming she had been forced into retirement last year in part because of a disagreement with her superiors over the accuracy of certain DNA tests.

There is more at stake here than Dr. Stajic’s retirement. The cutting-edge technique at the center of this legal dispute, called low copy number DNA analysis, has transformed not just police work, but also a range of scientific fields including cancer biology, in vitro fertilization, archaeology and evolutionary biology. Yet some of the technique’s applications have triggered scientific controversy.

The medical examiner’s office has become a strong advocate for the technique. It is the only public lab in the United States that uses low copy number DNA to develop profiles for use in criminal cases. But experts have long warned that investigators must take particular care in interpreting these tests: analyzing so few DNA molecules can lead to errors...