Joyner learned of the fate of his great-uncles, farmers Thomas and Meeks Griffin, during filming of the PBS documentary "African American Lives 2," which first aired in February 2008 and was based on research by Harvard scholar Henry Louis Gates Jr.
The program traces the lineage of 12 people, including Joyner. The host of "The Tom Joyner Morning Show" said he was stunned to learn of his South Carolina roots and two great-uncles he didn't know existed - much less of their execution.
"The records will show they did not do what they were executed for, and maybe now they can rest in peace," Joyner said from his Dallas studio.
He said a pardon would bring long-overdue justice, adding "I started trying to put myself in my great-uncles' position and tried to imagine what they must've been going through."
The Griffins were forced to sell their 130 acres to finance their defense. After they died in the electric chair on Sept. 29, 1915, Joyner's grandmother moved to Florida where the family's known history begins.
"It's very unusual for stories like this to be passed down from generation to generation among African-Americans. As a people, we don't like to pass along bad news about family," Joyner said.
In June 2008, Joyner, Gates and legal historian Paul Finkelman wrote Gov. Mark Sanford seeking a pardon. The case is scheduled Oct. 14 before the state's parole and pardon board.
If a pardon were granted, it would be South Carolina's first awarded posthumously in a capital murder case, said Pete O'Boyle, spokesman for the S.C. Department of Probation, Parole and Pardon Services.
Court documents show the Griffin brothers were executed with two other black men for the April 1913 shooting death of John Lewis, 73. Lewis was a wealthy veteran living in Blackstock, a Chester County town 40 miles north of Columbia.
The four were indicted July 6, 1913, and the trial began two days later. With only a day to prepare, defense attorney W.H. Newbold asked for a delay, but the request was denied. The state Supreme Court later deemed that denial insignificant.
Finkelman said such speedy trials were apparently once the norm and the decision wasn't necessarily racial - but it was unfair.
Joyner believes his uncles were framed.
Records show police initially focused on Anna Davis, a black woman Lewis was reportedly intimate with. She and husband Bart Davis were arrested with their suitcases packed. But attention later shifted when Lewis' stolen pistol was traced to John "Monk" Stevenson, a small-time criminal who first said he got the gun from Bart Davis' brother.
He claimed he was only a lookout when Lewis was killed. In a plea deal that spared his life, Stevenson - who is also black - named the Griffin brothers and the two others and testified against them. He later received a life sentence.
According to sworn statements, Stevenson told people in jail the four men he implicated knew nothing of the crime, but he named them to save himself.
When appeals failed, Newbold asked the governor for a pardon hearing.
Some white residents in Chester County agreed.
More than 120 people signed a petition to then-Gov. Richard Manning declaring "grave doubts as to their guilt" and requesting a reduced sentence. The signatures included people identified as Blackstock's mayor, a former sheriff, two trial jurors and the grand jury foreman.
A former detective wrote that information was withheld from the defense, and that Stevenson also told him the four convicted had nothing to do with the murder.
Finkelman, an Albany Law School professor, called the petition astonishing. In his decades studying Southern history, this is the first time he's seen petitions signed by prominent white residents in support of a black man accused of murdering a white man.
"It just didn't happen," he said. "The nature of South Carolina in 1900 was, if a black man was arrested for a crime like this, you could be pretty sure they'd be convicted and executed, and nobody would care."
Still, hundreds of residents signed petitions asking the governor to dismiss appeals for clemency and urging execution.
But the signatures of support show "everybody wasn't unfair," said Joyner, who grew up in Tuskegee, Ala. "It says something about the history of racism in South Carolina that everybody wasn't like that back then."
Nearly a century later, it's impossible to determine who did commit the murder, according to Joyner, Gates and Finkelman.
While a pardon isn't an apology, it means if the men were tried today, they likely wouldn't be convicted, said Joyner's attorney, Steve Benjamin.
"It was a sad period in our state's history and probably not uncommon," he said. "It doesn't undo what happened. It does allow the state to put its best foot forward."
Joyner said learning the family secret has changed his life.
"It's been mind-opening. When I see when and how far people have gone before me, it makes me stronger." He added, "There are probably so many stories like this that will never come to light, and their cases will never be heard."