A rape kit is a deceptively powerful tool, a cardboard box with envelopes, glass microscope slides, swabs, a comb and blank forms. As it journeys from hospital to police station to laboratory to court, the evidence within can lock up rapists, or free those arrested or convicted in error.

In the Duke Hospital emergency room on the morning of March 14, 2006, Dr. Julie Manly conducted a pelvic examination of Crystal Gail Mangum. Mangum said three men had gang-raped her for half an hour. The doctor also collected evidence: thong panties; swabs of the mouth, vagina and rectum; a cheek scraping; a blood sample; and hair from Mangum's head.

Manly made one physical finding: "diffuse edema of the vaginal walls," or generalized swelling. The doctor was assisted by Tara Levicy, a nurse in training to conduct rape exams.

The kit was passed from Levicy to Duke police to Durham police, who delivered it to the State Bureau of Investigation laboratory March 27.

The next day, agent Rachel Winn examined the swabs, slides and panties. She found no evidence of semen, blood or saliva. That ran against Mangum's accounts: She said that no condoms were used and that at least one man ejaculated, perhaps all three.

The following day, March 29, Durham District Attorney Mike Nifong started speculating publicly that the DNA test results might not match any of the lacrosse players. "I would not be surprised if condoms were used," he said.

It's unclear when Nifong learned that the rape kit had come up empty. On March 30, agent Jennifer Leyn called Nifong to discuss samples collected from the bathroom floor of the house where three lacrosse captains lived; SBI phone logs don't mention what else they discussed.

Nifong certainly knew by April 4 that the SBI found nothing in the rape kit; that's when agents from the lab updated him in a conference call. With no helpful evidence from the SBI, Nifong started looking for a laboratory that could perform more sensitive DNA tests.

Nifong found an eager scientist in Brian Meehan, director of DNA Security Inc. in Burlington. Meehan started his career as an academic biologist who specialized in studying mussels but gravitated to working in DNA laboratories in the 1990s, as DNA became a more powerful and sophisticated forensic tool.

An affable man with a strong Boston accent, Meehan opened his own lab in 1998. In recent years, he and his partners had aggressively marketed their lab. They conducted training sessions for police and public officials and offered private investigators discounts for multiple tests.

Meehan's lab could run tests so sensitive that they pick up DNA from a single cell.

Late on the afternoon of April 4, Meehan told Durham police he wanted in; Investigator Michele Soucie wrote that DNA Security "can possibly adjust prices because they would really like to be involved in case." Still, Meehan's work would eventually cost the state $28,610.

Nifong moved quickly. The next day, he got a judge's permission to perform the private tests, and the following day, April 6, a Durham police officer carried the evidence to Burlington, where it was tested April 7, 8 and 9.

On April 10, Nifong and his investigators went to Burlington to meet with the lab director. Nifong recently said he doesn't remember this meeting; however, Sgt. Mark Gottlieb and Investigator Benjamin Himan recorded it in their notes and narratives.

Meehan testified that he met Nifong on April 10 and told the prosecutor that he found no DNA of any of the players in the rape kit but that he found traces of DNA of unidentified men.

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