On 1 December 1984 the body of Liet Duong, aged 36 years, was located in a shallow grave in scrubland near Whyalla.
He was last seen alive on 26 October 1984 in Whyalla.
The cause of death of Mr Duong was not established and could not exclude natural causes.
The partner of Mr Duong was arrested and tried for offences relating to the disposal of the body and convicted.
This conviction was later quashed on appeal.
A reward of up to $200,000 is on offer to anyone who provides information leading to a conviction in the case.
Anyone with information is asked to contact Crime Stoppers on 1800 333 000 or at www.crimestopperssa.com.au