Robert Pendergast was reported missing by his mother on 27 May 1999.
She had last spoken with the then 31-year old on 6 February 1999 when he was staying in Adelaide.
He has not been seen or heard from since that time.
Prior to his disappearance Mr Pendergast had been arrested by NSW Police in April 1998 for his involvement in interstate cannabis trafficking.
It is known that he was staying with criminal associates in Adelaide during 1999 and it is believed that at least two of these associates are responsible for his suspected murder.
It is believed a drug debt is what led him to be shot at a country location east of Adelaide and his body buried.
The suspected murders of Mr Pendergast, David McWilliams, Leo Daly and 15-year old Juan Morgan continue to be investigated by Major Crime Investigation Branch under the title of Operation Jarrah.
The suspects for each of these murders are known to investigators however further information is required to provide evidence that would lead to the charging and prosecution of these suspects.
A reward of up to $200,000 is on offer for information that leads to a conviction and/or leading to the recovery of his remains.