Joseph Schexnider, who was 22, disappeared from the town of Abbeville in January 1984, after missing a court hearing over charges of possessing a stolen vehicle.
It is thought his family did not report him missing because police officers had arrived at their home searching for him following the missed court appearance.
Mr Schexnider’s mother said at the time that he had been known to leave abruptly – including once to work on a circus – and was this time thought to be on a “rendezvous”.
However, human remains were discovered with a pair of gloves, a cigarette lighter, a watch and a wallet in a chimney during renovations carried out to Abbeville National Bank in May.
This week DNA tests by a Louisiana State University laboratory confirmed that the remains in the chimney, which was sealed off later in the 1980s, were those of Mr Schexnider.