Law: DNA On Trial: Mixed results for genetic tests

The strange tale made banner headlines and gripping TV in 1985. Filled with remorse, Cathleen Crowell Webb publicly declared that Gary Dotson was not the rapist her testimony sent to prison in 1979. In fact, she said, there was no rape; she made up the whole story out of fear that she might be pregnant by her boyfriend. The best Dotson could obtain from that admission was a commutation of the remainder of his 25-to-50-year sentence. Last week, however, his name was finally cleared as Illinois prosecutors dropped all charges against him after a state judge ordered a new trial. The reason: results of DNA identification tests indicated that Dotson could not have been the man who had sex with Webb.

But in another case decided last week, a New York State judge raised some doubts about the courtroom use of DNA technology. Forensic DNA tests seek to compare the genetic patterns of a suspect or victim with those of the human remains, such as blood or semen, left at the scene of a crime. Proponents of DNA identification have long insisted that the tests are so precise that they can establish matches or exclusions to a near certainty.

In a precedent-setting ruling, New York Judge Gerald Sheindlin questioned the reliability of certain procedures employed by Lifecodes Corp., one of the nation's leading DNA-testing firms. Sheindlin agreed that DNA techniques "are generally accepted in the scientific community and can produce reliable results." But he ruled that in the murder case of Bronx janitor Joseph Castro, Lifecodes "failed in several major respects to use the generally accepted scientific techniques and experiments for obtaining reliable results."

Specifically, the decision means that the tainted tests may not be introduced to show that a bloodstain found on Castro's watch came from the victim, though other acceptable DNA tests by Lifecodes may be used to show that the blood does not belong to Castro. Beyond this immediate case, the ruling is expected to embolden many of the hundreds of defendants fingered by DNA tests around the country to challenge the procedures used to identify them.