How many other innocent people are rotting in jail?

The Raleigh News & Observer ran a series of stories last week about Dwayne Dail, who spent 18 years serving two life sentences for the rape of a 12-year old that he had nothing to do with.  Dail has been protesting his innocence all these years, but if not for a former police officer holding onto evidence from every case, Dail would have died in prison:

After 18 years living inside a prison cell, Dwayne Allen Dail's must-do list read like the menu of a country kitchen.

Pork
chops for Tuesday dinner at his brother's. Country ham and gravy for
breakfast today. His mom promised to make him a peanut butter and
molasses sandwich for a snack.

Dail, 39, left his youth behind in
prison, paying for another man's crime. Dail was 19, a day laborer and
an aspiring rock singer when Goldsboro police arrested him on charges
of raping a 12-year-old girl after breaking into her home.

Monday,
DNA evidence extracted from the girl's nightgown, forgotten since the
night of her rape nearly two decades ago, proved what Dail had sworn
all these years: He was innocent.

And from the N&O editorial:

It boiled down to one of the most dramatic illustrations yet of the
value of DNA testing in the world of criminal justice. And the DNA
evidence came to light only after the N.C. Center for Actual Innocence,
a nonprofit clearinghouse for innocence claims, persuaded the Goldsboro
police to keep looking for any items retained after the 1987 rape.

When
a nightgown belonging to the victim surprisingly turned up among old
files, off for testing at the state crime lab it went. And the DNA it
yielded showed that Dail couldn't have been the rapist.

The case
had relied mainly on the girl's confident identification of Dail, along
with the resemblance between a hair taken from a rug in the bedroom and
Dail's hair.

But her courtroom description of the attacker didn't
jibe well with Dail's appearance at the time. It also turned out that
the rug had been bought second-hand, so there was no telling where the
supposedly incriminating hair might have come from. And the hair
resemblance in any event only involved outward characteristics of the
strands that were apparent under a microscope — no sophisticated
testing.

How many people will wrongly spend their lives in jail because they weren't lucky enough to have long forgotten DNA evidence turn up?  Sure, you have to figure most of those people in prison proclaiming their innocence are surely lying, but the more I learn about the criminal justice system, the more I suspect most of us would be shocked if we knew the true percentage of innocents incarcerated.  It is also worth mentioning that without strong corroborating physical evidence, eyewitness identification is worse than worthless.  It works to put innocent people in jail time and time again.  Heck, “My Cousin Vinny” was clear enough on that point.