Last week, the DNA test results for an alleged rape involving the Duke men's lacrosse team came back as negative matches to evidence obtained from the victim.
With defense attorneys and District Attorney Mike Nifong disputing the significance of the findings, experts have expressed similar disagreement over the results' true meaning.
The Raleigh forensics lab, where the lab where the DNA results of the 46 Duke lacrosse players were sent, was audited a year ago as a result of a complaint from an attorney, said Ralph Keaton, executive director of the American Society of Crime Laboratory Directors.
ASCLD found no evidence of any wrongdoing on the lab's part.
Joe McCulloch, a criminal lawyer and the head of the Innocence Project of South Carolina-a program that works to free wrongly accused inmates with DNA evidence-said it is extremely difficult to dispute the accuracy of DNA tests if the samples were gathered correctly.
Nifong, however, said last week that he was awaiting the results of a second round of DNA tests, noting that he is still convinced a sexual assault occurred.
The first round of tests the players underwent were bacal exams, which involves having the inside of one's cheek swabbed for a sample of DNA. Nifong has not disclosed the nature of the second test.
Kari Converse-a consultant for the Innocence Project in New Mexico-said more tests may have been ordered because it was difficult to sort out evidence from the sheer amount of DNA gathered.
"The standard testing that is done in most cases is called short tandem repeat," Converse said. "It can take a very small amount of DNA-the size of a grain of sand cut into 20,000 pieces."
Converse explained that DNA testing is particularly helpful in rape cases because the forensic analysts look for the Y chromosome exclusive to males in the vaginal sample taken from a female victim.
Identifying a particular individual once a male sample has been found, however, is more difficult.
"There's a long strand of DNA inside the nucleus [of a cell] that is coded with everything that makes us human," Converse said. "98 percent of that you'd find in a chimp, [but] there's a small amount of that that makes us a human being."
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She added that the part of DNA that differentiates human beings from one another is minute.
"That's what they test when they do DNA testing for forensic purposes," Converse said.
DNA tests were first used to convict someone in 1988, and since then they have been regarded as a very reliable source of evidence.
The tests have a wide array of applications and have been used to convict murderers, rapists and other criminals, as well as to free the innocent or clear a suspect's name years after his or her death.
Amy Bejsovec, an associate professor of biology at Duke, explained that DNA "fingerprinting" is better used to eliminate someone from being suspected of a crime than to convict an individual because there is a statistical probability that two people may have very similar DNA "fingerprints"-especially within the same ethnic group.
Converse said a more likely explanation for a DNA profile match between a suspect and an individual in the general population-the chances of which are astronomical-is the possibility of lab error or fraud.
"In my work I've had one error in probably 15 to 20 cases," Converse said. "Does that mean that labs make mistakes in every one out of 15 or 20 times? No. [But] labs like to say, 'We don't make any mistakes'-but they do."
McCulloch said the magnitude of the testing done in the lacrosse case demonstrates the state's commitment to gathering accurate samples.
Susannah Baruch, the director of the Genetics and Public Policy Center at Johns Hopkins University, however, agreed with Converse's assessment.
"Most medical labs are inspected by the federal government and are held to a particular standard-based kind of testing," Baruch said.
"But in the area of molecular genetic testing the government has not yet devised a test to make sure the lab is doing tests properly."
She added that because of this lack of oversight, mistakes can range from mislabeling samples to losing them completely.
Keaton, whose organization publishes standards of operations for crime labs and inspects them, said ASCLD goes through extensive procedures to make sure forensic labs are up to code in a "very detailed process."
"Before even going in, we review the operating procedures and the statements of qualification for the individuals in the lab," Keaton said.
"Then we go interview lab personnel, verify documents, examine competency records-do whatever is necessary. They're required to undergo inspection every five years but they may be subjected to more frequent audits if there are complaints."