Steven Barnes, now 43, was wrongfully convicted of rape and murder at the age of 23.

Stephanie Smith

CNN Medical Producer

For 20 years Steven Barnes has relived one day over and over in his mind; the scenes sometimes unfold like a filmy, disjointed dream, and sometimes with a stark and painful furor.

It was the day he was arrested, at age 23, for a crime he did not commit.

"When they came to arrest me I was screaming and freaking out saying I didn't murder nobody," said Barnes, who is now 43, and was released from prison last November just a few days after his conviction was overturned.

His conviction hinged on what he calls "junk science." In 1989, Barnes was convicted of raping and strangling to death 16-year-old Kimberly Simon on the evening of Sept. 18, 1985, in Marcy, N.Y. The case against him relied heavily on forensic evidence and he spent nearly 20 years in prison.

Investigators testified that hairs found in Barnes' truck had similar characteristics to hairs found at the crime scene. They suggested dirt found in the wheel wells of his pick-up truck was similar to dirt at the crime scene - and the clincher - according to investigators, a smudge on the side of Barnes' truck bore a similar imprint to the jeans worn by the victim. Barnes says investigators suggested that the victim leaned against the truck before he allegedly raped and killed her.

It is all of these suggestions that still make Barnes bristle.

"That was all their scientific evidence," said Barnes, with an air of scorn at the word 'scientific'. "It was all about similarities. Similar hair, similar jean imprint. You don't put someone away that long for similarities."

"What you have is a reliance on forensic disciplines that have not been fully vetted, that aren't sufficiently rooted in science," said Eric Ferrero, a spokesperson for the Innocence Project, the organization that pushed for the DNA testing that ultimately debunked forensic evidence used against Barnes.

Ferrero says that although forensics is an inexact science, juries in cases like Barnes' can be easily swayed. Of the 241 wrongful conviction cases the Innocence Project has helped to overturn, 50 percent of them hinged on forensic science problems.

"It's not like what you see on [television drama] CSI," said Ferrero. "In court, a forensic analyst cannot say something 'definitely' matches, they can't say this fiber 'definitely' belongs to a suspect. They just can't say those things because the science is not there.

"We do have cases, where during the trial someone was convicted based on no real evidence."

"The issue is, we need more science in forensic science," said Paul Giannelli, a law professor at Case Western Reserve Law School.

A report by the National Academy of Science in February issued a scathing assessment of the forensic science community. It stated that, among other issues, "testimony based on faulty forensic science analyses may have contributed to wrongful convictions of innocent people."

While most scientists agree that DNA evidence is the gold standard of forensics – and that toxicology also has a scientific basis – other areas are increasingly being assailed. One such area is called pattern or impression evidence.

Ferrero says pattern evidence problems crop up often in Innocence Project cases.

"It's shoe prints, tire tracks, bite marks, markings on bullets, lip impressions," said Ferrero. "We're not saying that those are all junk science necessarily, we just don't know if they are junk because there has never been testing done."

The most popular piece of impression evidence is fingerprinting. It has been used in criminal cases since the 1930's, said Giannelli, and was once considered infallible.

"[Forensic investigators] say that this is your fingerprint to the exclusion of all other people in the world," said Giannelli. "That's an incredible statement. DNA doesn't even do that."

A small study by the University of Southampton in 2005 put fingerprinting to the test.

Researchers at the School of Psychology invited a panel of forensic experts to assess a set of fingerprints. In a twist to the study, the scientists were led to believe that the prints they were comparing did not match - and in a further twist, all of the samples being analyzed by the experts were prints they had "matched" before in previous cases.

The results are stunning. Only one participant concurred with his previous assessment that the prints were a "match." Three scientists changed their original decision, and one expert could not render a definitive decision.

The results, says Giannelli, reveal serious flaws not only with fingerprint analysis, but the forensics field in general.

“All of this court testimony [by forensics experts] is being done without any statistical basis,” he said.

He adds that fingerprinting, and many other elements of forensic science as exercised at an estimated 400 labs across the U.S., is suggestible and subjective.

That subjectivity has played out in harrowing ways. In 2004, the FBI, following the terrorist attack on commuter trains in Madrid, errantly linked a fingerprint found at the crime scene to Brandon Mayfield, a U.S. citizen.

The FBI determined that the fingerprint image at the scene - which was tested and "matched" to Mayfield - was of "substandard quality," owing to the mistake.

But if the FBI can make that mistake, Giannelli marvels, what are the mistakes being made at less sophisticated forensics labs around the country?

"Comparing a mark on malleable surface is a dynamic action," said Giannelli. "Even if your fingerprints are unique, you have to accept that you're not looking directly at fingerprints, you're looking at a smudge. Every time you put a finger on a smudge it's a distortion

"And yet courts allow this in hundreds of cases accepting bite mark evidence, fingerprint evidence, other impression evidence, and it's never been successfully challenged."

At the Georgia Bureau of Investigation (GBI) in Atlanta, deputy director Dr. George Herrin is adamant that forensics is reliable. He stresses the importance, when thinking about solving crimes, of seeing the big picture.

"Everything has value," said Herrin. "Everything that the crime lab does is based upon valid scientific principles. There are different levels of discriminating power that the different tests have."

And yet, the furor and frustration about forensics is building outside of labs like the GBI. Many, even within the field, agree that something needs to change - soon.

Dr. Bruce Goldberger, a professor of toxicology at the University of Florida College of Medicine, echoes the findings of the NAS report - which calls for more scientific rigor, oversight and funding for forensics.

"In the short term [it is] a way to elevate the integrity of the science," said Goldberger.

While the forensics field undergoes a sea change, Steven Barnes is experiencing his own. He is acclimating to life outside of prison.

He says that he is not bitter, because that would be a burden, but he is still concerned about the shaky precipice upon which he says justice is doled.

"It's just that you don't want to put someone away for that amount of years based on 'maybe', 'perhaps,' and 'could have been'," said Barnes. "It just needs to change."