Yet to be determined, the [official] report said, was whether the lapses were "isolated breakdowns or only the tip of an iceberg." Among cases to be studied were three high-profile convictions, including one for murder, based on faulty laboratory evidence.

"The findings are extremely troubling," said [investigator] Mr. Bromwich, a partner at Fried, Frank, Harris, Shriver & Jacobson, in an interview after presenting his report. But he said, "Houston is not alone in having this problem." As the Justice Department's top internal watchdog from 1994 to 1999, he exposed sloppy work and false testimony by F.B.I. laboratory scientists. Other state crime labs have also come under fire.

But some of the Houston's report's language was particularly scathing. By the time a state audit in 2002 confirmed problems exposed by a local television station, KHOU, Mr. Bromwich reported, "the DNA Section was in shambles - plagued by a leaky roof, operating for years without a line supervisor, overseen by a technical leader who had no personal experience performing DNA analysis and who was lacking the qualifications under the F.B.I. standards, staffed by underpaid and undertrained analysts, and generating mistake-ridden and poorly documented casework."

Tropical Storm Allison in 2001 flooded the laboratory, and in 33 homicide and rape cases, employees were quoted as reporting, "this biological evidence had become so saturated with water that they observed bloody water dripping out of the boxes containing the evidence and pooling on the floor." (emphasis added).

Forensic scientists who have reviewed the department's work on the case say there were numerous problems with the lab's technique and its conclusions.

First, the lab misidentified the source of a semen stain found in the backseat of the woman's car, according to William Thompson, a California criminology professor who specializes in forensic science and has reviewed the Sutton case. The lab concluded the stain contained a combination of DNA from Sutton, the victim and the second attacker.

But, Thompson said, neither Sutton nor the victim's DNA was present in that sample, suggesting it came from a single source. If that single source is one of the two rapists and his profile is compared to other samples, such as the vaginal swabs that contained DNA from all three parties, analysts would be able to separate the profile of the second rapist. Based on the evidence, Thompson said, Sutton could not have been the second attacker.

Further, during Sutton's trial, a police crime lab employee offered testimony that suggested the DNA found on the victim was an exact match for Sutton's. In reality, however, 1 in 16 black men would have a similar match, Thompson said.

Beyond false conclusions and misleading testimony, the police lab conducted shoddy work, DNA experts say. Analysis consumed all four vaginal swabs taken from the victim in its testing, limiting the possibility for retesting to one vaginal smear with limited DNA.

Thompson and Dr. Elizabeth Johnson, the DNA expert working for Sutton, said most labs would use a much smaller portion of the rape kit for testing.