After all this time, her murderer remains at large.

The 22-year-old's badly damaged body was discovered in Burrenjim Dam - near Stockrington - on Anzac Day, 1994.

The mother-of-two died of massive head injuries. She suffered 11 skull fractures before sandstone pieces were put into her clothes and she was tossed into the water.

Police believe she could have been dead for as long as six days before she was found floating near the weir wall.

After more than a quarter of a century, an inquest in the late 1990s and many appeals for information, NSW Police on Wednesday announced a $1 million reward for help solving the case that has devastated a family for decades.

Melissa's brother Peter Hallett told the Newcastle Herald the reward was a "welcome surprise" to the family, who had been re-interviewed in recent months as investigators under the new Strike Force Circulo have pored over the mystery.

In October, police returned to the spot at the dam where Melissa's body was found and they have conducted more forensic tests on evidence picked up soon after her death.

"Obviously it shows there is very strong intent from the police to move forward with this case," Mr Hallett said.

"There has definitely been a shift in recent months."

Mr Hallett spoke at the reward announcement in Sydney on Wednesday, saying his adopted sister - nine years his junior - was "deeply loved and we've never stopped missing her".

He urged anyone with information about the murder to speak up, to "let Melissa and all who love her finally have a small measure of peace".

Police said they were looking for particular people - who remain unnamed - who lived in the Newcastle-Lake Macquarie area in 1994 but had since moved to Queensland, Victoria and South Australia.

Melissa's former husband Scott Hunt, who has long professed his innocence, told the Herald police visited him last week and told him he was no longer a person of interest.

The State Crime Command confirmed on Wednesday they had spoken with Mr Hunt recently but would not comment on who was or was not a person of interest.

"I hope [the reward] leads to arrests very soon," Mr Hunt said.

Mr Hallett told the Herald he believed there were people somewhere sitting on information that could help bring his sister's murderer to justice.

"She had a lot of friends, there were a lot of people who knew her," he said.

"I can't believe that there aren't people who became aware of some of her last movements and what happened to her. Maybe they don't know beyond a shadow of a doubt but I'm pretty convinced there are people out there who know things.

"Twenty-six years have come and gone, it might be a good time to get those things off your chest."

Melissa's parents Ron and Jan adopted her when she was six-weeks old - she was the youngest of their three children.

The struggles of her teenage years and young adulthood have been well documented since she was murdered - she spiraled into prostitution and drug use.

But Mr Hallett said his sister's life should not be summed-up by her death or "the mistakes she made in her short life".

Melissa's parents are now in their late 80s and her two children are grown.

"When you start to focus on what happened, it can easily take over your life," Mr Hallett said.

"It kind of seeps into everything you do. You don't even realise the impact of it and how things might have been different.

"It's such a brutal act and it plays on your mind so often and it catches you when you least expect it."

Anyone with information that may assist Strike Force Circulo detectives is urged to contact Crime Stoppers: 1800 333 000 or https://nsw.crimestoppers.com.au.

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