So Ferguson enlisted the help of a national group that works to exonerate the wrongfully convicted and successfully petitioned a Genesee Circuit judge to order DNA tests -- a now-common practice that was not in use by Flint police at the time Ferguson was convicted.

The result? Ferguson was told there was only a 1 in 2.2 quadrillion chance that the DNA found at the crime scene wasn't his.

DNA evidence cuts both ways, said Donna McKneelen, co-director of the Thomas M. Cooley Law School Innocence Project, which helped Ferguson with his DNA request.

"We caution them before we move forward: Do you really want to take this chance?" said McKneelen, who said she was not prepared to discuss specifics of Ferguson's case. "That's something I don't understand (cases in which DNA testing confirms a prosecutor's case) because it causes more problems" for the accused. Ferguson, now 47, was sentenced to 60 to 90 years in prison in 1986 after a jury convicted him of robbing and raping the 32-year-old postal worker from Clio on her first day on a new route on Flint's north side.

The late Donald Freeman, a county Circuit Court judge, called Ferguson a "predator" during sentencing, even though the Benton Harbor native protested he was innocent.

Only 21 at the time he was sentenced, Ferguson's criminal record already included two prior adult convictions beginning at age 9, according to Flint Journal files.

Ferguson, aided by The Innocence Project at Cooley, petitioned for a Genesee Circuit Court order to carry out DNA testing on decades-old vaginal swabs, panties and uniform pants that were collected from the victim after the attack.

Genesee County Prosecutor David Leyton said some inmates convince themselves they are not guilty in a case, even though all evidence suggests otherwise.

"A lot of folks in prison say (they) didn't do it," Leyton said. "In this case, he did do it. I don't believe there are many innocent people locked up."

Founded in 1992 by Barry C. Scheck and Peter J. Neufeld, the Innocence Project, was established to assist prisoners who could be proven innocent through DNA testing.

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DNA test request backfires against convicted Flint rapist