Josiah Sutton was convicted for rape after a Houston laboratory told the jury that his DNA matched the rapist's. But new testing has confirmed otherwise. He was innocent, and spent 4 1/2 years in jail for a crime he didn't commit. His sentence was 25 years.

The retesting is part of a review of the laboratory that began after a scathing state audit of its work led to a suspension of genetic testing in January. Mr. Sutton's apparent exoneration is the first to result from the review.

Legal experts say the laboratory is the worst in the country, but troubles there are also seen in other crime laboratories. Standards are often lax or nonexistent, technicians are poorly trained and defense lawyers often have no money to hire their own experts. Questions about the work of laboratories and their technicians in Oklahoma City, Montana and Washington State and elsewhere have led to similar reviews. But the possible problems in Houston are much greater. More defendants from Harris County, of which Houston is a part, have been executed than from any other county in the country.

"This is an earthquake," Mr. Sutton's lawyer, Bob Wicoff, said. "The ramifications of this for other cases, for death penalty cases, is staggering. Thousands of cases were prosecuted on the basis of this lab's work."