A South Carolina judge has overturned the 1944 conviction of 14-year-old George Stinney Jr, the youngest person to be executed by the United States in the last century.

Judge Carmen T. Mullen of Circuit Court called the case, which saw Stinney executed by electric chair after being found guilty of the killing of two white girls in a one-day trial, a "great and fundamental injustice".

He was arrested, convicted of murder and executed in the space of three months without an appeal. The trial lasted three hours and a jury of 12 white males found him guilty in ten minutes.

He was accused of the murders of Betty June Binnicker, 11, and Mary Emma Thames, 8, in 1944 after they were beaten and killed with an iron spike in the segregated town of Alcolu, South Carolina.

Authorities claimed that Stinney confessed and he was kept away from his parents, according to records from the time of his arrest. His supporters claim that he was a scared, young boy that would say anything to please the authorities.

At the hearing to overturn the conviction in January, Stinney's two sisters testified and a video deposition was given by his brother. Almost every witness in the case has died since the incident.

"I am not aware of any case where someone who was convicted has had the trial conviction and sentence vacated after they'd been executed," Miller W. Shealy Jr., a professor at the Charleston School of Law, told the New York Times.

The United States abolished the death penalty for children under the age of 18 in 2005.