Reward at $1 million as police search for Mr Rosson and Mr Hogg

"It is never too late to come forward.

"Relationships and loyalties change, people who were once scared may no longer be, and we would encourage these persons to come forward," Queensland Police Service detective acting inspector Adam Bennett said.

"Police would like to directly appeal to the LGBTIQ+ community or anyone who knew Mr Hogg leading up to his death in March 2002 as he was a very private person, and any personal information may assist with this matter," he said.

Witnesses said they saw Mr Hogg's "distinctive red Toyota Celica" at a carpark in Tweed Heads, NSW, on March 11 2002.

They allegedly saw a flash and heard a loud bang.

Police believe Mr Hogg was shot and his body was placed in the Tweed River but his remains were not found during searches.

That same distinctive red Toyota Celica allegedly appeared at a property in Mt Nathan, Queensland three days later on March 14. The property belonged to Mr Rosson.

Police believe he has agreed to show two men a firearm that was advertised for sale between 11am and 1pm.

Mr Rosson died that day after suffering a gunshot wound.

The red Celica was found abandoned at Palm Beach, Queensland on March 20, 2002.

IN OTHER NEWS:

Acting inspector Chris Elliott said that much remained unclear but investigators believe the same people were responsible for each murder.

"We are confident that the car used to access Mr Rosson's home was Mr Hogg's Toyota Celica, and we believe the same men were involved in each incident," he said.

"The families of these men deserve closure having dealt with the uncertainty of what happened over two decades ago.

"To those in the community who know what happened to Mr Rosson and Mr Hogg, and it's time for you to come forward."

Anyone with information that might assist investigators is urged to contact Crime Stoppers on 1800 333 000.