A $500,000 reward has been offered to help solve the suspected murder of a Queensland man last seen more than 40 years ago.
Anthony Jones, 20, last spoke with family in November 1982, telling them he planned to hitchhike from Townsville to Mount Isa, police say.
He was last seen on November 12 in the town of Hughenden, in the state's northwest.
Mr Jones never arrived in Mount Isa.
Police have increased the reward amount a number of times over the four decades since Ms Jones disappeared, but are hopeful the $500,000 will finally help solve the mystery.
"More than 40 years has passed now and in that time loyalties change, any information no matter how small or insignificant it may seem, could be the key to bringing closure for Tony's family," Detective Sergeant Brenden Stevenson said.
Police said multiple witnesses placed Mr Jones in Hughenden on November 12, indicating he attended the Grand Hotel and may have been involved in an altercation.
By January 1983, police say they received a letter postmarked from Cairns by someone named "Lochiel" indicating Mr Jones may have been buried in the Fullarton River, in the state's northwest.
An extensive search of the area the next day did not find anything.
A number of persons of interest have been investigated over the years, along with numerous searches of areas including the Cloncurry River and Hughenden.
Mr Jones was carrying a Voere .22 calibre rifle with serial number 257435, a large blue backpack with aluminium framing and green sleeping bag, a green one-man tent, and various personal items.
None of the items have been recovered.
Investigators believe Mr Jones was murdered.
In 2002, the state coroner ruled Mr Jones had died at the hands of a person or persons unknown.
The inquest was reopened in 2010 and held over 2016-17, with a date to be advised for the findings.
"It is never too late to come forward," Det Sgt Stevenson said.
"We are also urging anyone with any information at to the whereabouts of Tony's rifle, or the identity of the person who posted police the letter from Cairns in 1983, to please contact police."
