The Innocence Project petition filed earlier this month for convicted serial killer Billy Glaze to get a new trial relies heavily on newly-analyzed DNA evidence from decades-old crime scenes.
But is the science solid?
Sophisticated DNA analysis that can identify a person's genetic fingerprint today didn't exist when Glaze went to trial in the late 1980s for the murders of three American Indian women in Minneapolis - Kathleen Bullman, Angeline Whitebird Sweet and Angela Green.
Glaze, who was a drifter, became the prime suspect in the serial murders, was arrested and convicted based mostly on witness testimony, but little physical evidence.
Hamline University forensic science professor Glenn Hardin says at the time of Glaze's trial DNA analysis was in its infancy.
"DNA is important and tells you something," Hardin said. "If the DNA is properly preserved and analyzed it is very accurate."
With scientific advancements in DNA testing, the Innocence Project claims to have helped exonerate hundreds of people around the country.
In the Glaze case, the Innocence Project had dozens of pieces of evidence from the three crime scenes tested for DNA according to its petition filed in Hennepin County Court this month. An Innocence Project attorneys say the results not only prove Glaze was wrongfully convicted, but point to the real killer.
In its petition, the Innocence Project says lab results show Glaze's DNA was not found at any of the three crime scenes, but the DNA profile of another man was found at two of the crime scenes - on a rape swab from one of the victims and on a fresh cigarette butt found near another victim.
Here are key questions about new DNA testing on old evidence
Q: The evidence gathered from the Minneapolis crime scenes is decades old. Does the ability to find DNA deteriorate over time?
Pam King is a Minnesota public defender and DNA expert. King was recently named to the new National Commission on Forensic Sciences to help create nationwide standards and guidelines for how forensic science should be conducted.
King said being able to find biological evidence which can lead to DNA on something collected from a crime scene can be influenced by things like heat, moisture and time. She says time can create some limits, but not always.
"There's still very rich amounts of information that are available and especially in a case such as this, where the types of DNA that were being looked at come from bodily fluids that are very rich sources to begin with," said King.
In the Glaze case, King says there are two rich sources of DNA - saliva on the cigarette butt and semen on the rape swab. Because the sources are rich, the DNA doesn't go away just because it was deposited nearly 30 years ago. DNA is fragile and can break down over time, but as long as the evidence was stored properly, scientists can still find biological materials and DNA years later.
Q: What are some of the limitations of DNA?
A: Solving crimes doesn't just happen because of one piece of evidence, say Hardin and King. Investigators can solve crimes because they put several pieces of the puzzle together. DNA is a piece of that puzzle.
While it can give you some information, forensic experts say DNA doesn't give you all the information. DNA can tell you that someone was in a particular place, but how did that DNA get there and what were the circumstances as they relate to the crime? Investigators can't answer those questions with DNA alone.
In the Glaze case, there is DNA on a cigarette butt, according to the Innocence Project. The DNA proves someone had contact with that cigarette but doesn't really answer some of the other important questions, including: Why was the cigarette butt located at one of the murder scenes and is the person who touched it the killer?
Q: How can the Innocence Project conclude that Glaze is not the killer and this other person whose DNA profile was found in two places is the killer?
A: The Innocence Project is putting together pieces of the puzzle. You have the same DNA profile found at two of three murder scenes. Out of everyone in the national DNA database, the person to whom this profile belongs comes back to a man living in Minneapolis. The man happens to be a convicted rapist who served time in prison for a 1989 rape of an American Indian woman. These are just some of the puzzle pieces Innocence Project attorneys say point to someone else.
Q: Could the Innocence Project be wrong?
A: Yes. Nothing human is foolproof. But what if the Innocence Project is right and an innocent man has been behind bars for nearly 30 years? Pam King says DNA analysis has helped the justice system make great strides.
"We do not want people to lose their liberty simply because we got it wrong," she says. "But the fact of the matter is that sometimes we do and sometimes it's because of the limitations of the resources that we had available at the time. Here, with DNA in these kinds of cases, it really is opening up new doors."
In response to the Innocence Project's petition for a new trial for Glaze, Hennepin County prosecutors have said the evidence against him is still overwhelming and the person whose DNA profile was found at the crime scenes is insubstantial. They'll be reviewing the DNA results and may put together their own version of the puzzle.