In 1959, when James Carter led fellow prison inmates in a rendition of the melancholy work gang song "Po Lazarus", he barely took any notice of the man making a recording. In the years that he followed he never thought about it once.
Now Mr Carter, 76, has been handed a platinum copy of the soundtrack to the film O Brother, Where Art Thou?, a royalty cheque for $20,000 (£12,000) and the promise of more money to come. Unknown to the former convict, his singing had been featured on the Coen brothers' Grammy award-winning film.
"I sang that song a long time ago," Mr Carter told The New York Times, after being informed that his soundtrack was outselling the latest records by Michael Jackson and Mariah Carey.
The recording was made by Alan Lomax, a musical archivist and writer who was travelling through the American South and visited the Mississippi State Penitentiary at Lambert, where Mr Carter was serving time for a weapons offence.
The recording of Mr Carter made by Mr Lomax, now aged 87, was discovered in the archive by T-Bone Burnett, the producer of the soundtrack. "It just made such a deep impression," he said. "It was such a beautiful version, a soulful version of a great song."
Mr Carter, who went on to work as a shipping clerk, was tracked down by the Lomax archive organisation, Mr Burnett and a reporter with a Florida newspaper who was working on a project about Mr Lomax's life. Now living in Chicago, he was persuaded to fly to Los Angeles with his wife and daughters to attend the Grammy ceremony last week.
He has now returned to Chicago, where he can expect royalties that could reach six figures.