It follows the opening of an inquest in Co Donegal yesterday to discover if the body is that of Noel McGlynn of Ballaghderg, Letterkenny.
Mr McGlynn, 26, went missing on June 17, 1983, and was never seen again.
Just nine days later, a body was found on a beach in Dunfanaghy.
The body was buried in an unmarked grave at the local Holycross Graveyard.
Now the brother of the missing man believes it was his body which washed up near Horn Head on June 26, 1983.
James McGlynn told the inquest he was convinced the body was that of his brother, whom he last seen at the family home.
Pathologist David Barry said a postmortem on the body on June 27 showed no sign of a violent death but there was no way of identifying a cause of death.
Coroner John Cannon said he was satisfied that tissue samples from the body could be matched with saliva samples taken from James McGlynn by gardaí and solve the mystery.
He adjourned the case until January 17.