Killen was found guilty of three counts of manslaughter on June 21, 2005, the 41st anniversary of the so-called "Mississippi Burning" case and received a much lighter sentence than the Scott sisters.
According to court records, the Scott sisters were found guilty of luring two men down a road where the Patrick boys used a shotgun to rob the men. No one was injured and the gun was reportedly never found.
The sisters was convicted of two counts of armed robbery and sentenced to two life sentences.
Gladys and Jamie Scott had known the Patrick boys because they had worked together at a factory. On the night of the crime, the sisters were driving to the store when Jamie Scott's car broke down. An acquaintance of Gladys from her factory job picked the girls up and began to harass them sexually, according to Halima Olifema, who is a member of the Free the Scott Sisterscommittee.
"One of them feigned getting out of the vehicle and so they were able to get out of the car," she said. "The girls walked away from the car and then went about their business. The following day, the sheriff's department came to their home and said they were implicated."
According to Olifema, the boys were coerced into testifying against the girls. "They, too, were scared," she said.
"They never should have been placed in jail at all," Olifema said of the sisters. "Even if they were not innocent, people who are literally murdered only get a slap on the wrist and don't even get six months in jail."
Barbour's press secretary Dan Turner told ABCNews.com that the amount reportedly taken in the 1994 robbery, $11, was "an urban myth," and at least several hundred dollars was netted in the crime.
"The other thing to remember was the sentence was not handed out by a judge, but by a biracial jury of their peers," he said.
For years, civil rights activists called for their release, saying the sentences were excessive. Those demands gained traction when Barbour asked the Mississippi Parole Board to take another look at the case.
Parole Board Chairman Shannon Warnock had said the board would read the sentencing guidelines and delivered on his promise to have a decision by the end of the year.
The governor's press secretary Turner said Barbour had pursued their release because Jamie Scott needed a transplant.
"There was a medical necessity, as a preferential consideration," he said. "It's also expensive for the taxpayers to keep a seriously ill person incarcerated. If [Jamie] can have this procedure, it very likely will be done through Medicaid…There are a lot of facets to it and there are arguments on each side of the ledger."
The sisters are also hoping to be allowed to move to Pensacola, Fla., to be with their mother, Evelyn Rasco, who led the fight for her daughters' release. Rasco did not return calls from ABCNews.com.
"We think they will be released in a week or two," said the sisters' lawyer.
Barbour is a Republican in his second term who has been mentioned as a possible presidential contender in 2012. He said the parole board agreed with the indefinite suspension of their sentences, which is different from a pardon or commutation because it comes with conditions.
An "indefinite suspension of sentence" can be reversed if the conditions are not followed, but those requirements are usually things like meeting with a parole officer, according to Turner.