A South Carolinian executed at age 14 in 1944 has been exonerated after a judge vacated his murder conviction on Wednesday. George Stinney Jr. is believed to have been the youngest person put to death in the United States in the 20th century.

NBC News reports the black teenager was convicted of using a railroad spike to beat two young white girls, ages 8 and 11, to death in Alcolu, South Carolina. Officials said he admitted to the killings, and a jury of 12 white men took 10 minutes to find him guilty.

Stinney was executed within three months of the incident. At the time, Stinney weighed just 95 pounds and had to sit on a phone book in the electric chair.

Stinney's sister maintained she was with him on the day of the murders, and her brother could not have committed them.

Civil rights advocates took on his case and spent years trying to get the case reopened, arguing that the boy's confession was coerced.

The appeal of Stinney's conviction brought by his two surviving siblings was finally successful on Wednesday when Circuit Judge Carmen Mullen threw out the verdict, writing that the speed in which the state processed through the justice system was as shocking and extremely unfair, the Charlotte Observer noted.

"I can think of no greater injustice," the judge added.

The main arguments for the appeal were the brevity of the trial and the lack of so much as a transcript of the proceedings. The only apparent evidence against Stinney was a confession a white police officer obtained without any parent or guardian present. At the time of the crime, 14 was the legal age of criminal responsibility in South Carolina.

The murders of 11-year-old Betty June Binnicker and 8-year-old Mary Emma Thames, whose bodies were found in an Alcolu ditch on on March 24, 1944, will likely remain unsolved, the newspaper suggested.

"There's not going to be a new trial after this," said Matt Burgess, one of the attorneys who handled the Stinney family's appeal. "The judgment has been vacated entirely because the judge found it was a fundamental violation of due process."