New information, of any description, which will give them reason to hope again. And not from just anyone, but from one of the thousands of inmates living in correctional centres across NSW.

Playing cards featuring victims of cold cases - unsolved homicides or suspicious disappearances - have been introduced into the state's jails this week. The project, Operation Veritas, has been planned over many years in close consultation with the victims' families, including Peter Hallet, the older brother of missing Hunter woman, Melissa Hunt.

Mr Hallet, who attended the launch at Sydney Opera House on Wednesday, said he felt lucky to be one of the families involved.

"There are apparently 500 unsolved homicides right now in NSW and so 52 families were privileged to be part of this first deck," he said. "We are very mindful that there are many other families looking for opportunities, a lot of them in the Hunter region."

The faces of other Hunter-based cold cases which feature on the cards include Roslyn Reay, who was stabbed to death in her Laman Street home in 2005; Allison Newstead, who was 17 when she was killed and dumped just outside Cessnock in 1993; and Revelle Balmain, 22, who never met her mother at Newcastle train station as planned in November, 1994.

The police are still investigating the murder of Melissa, who left behind two children - Jayde, who attended the launch along with her uncle, and her brother Luke. Mr Hallet was 31-years-old when his younger sister went missing.

"We are still waiting," he said. "We know that often people have information and they just need the right moment and the right prompts to think about actually telling what they know, so we are really hoping these playing cards reach the right people and that something comes forward that solves Melissa's case and lets us know what happened to her back in 1994."

The cards are a joint initiative between the NSW Police Unsolved Homicide Unit and Corrective Services NSW - in partnership with Crime Stoppers and the Homicide Victims' Support Group.

The cards were produced and distributed by inmates working at Corrective Services Industries. Corrective Services NSW Commissioner Kevin Corcoran said he was delighted that inmates have the opportunity to be involved in the production process.

"We are proud to be part of an initiative which sees our talented CSI overseers equip inmates with new skills to improve their prospects of rehabilitation and employment upon release."

NSW Police Force Homicide Squad Commander, Detective Superintendent Danny Doherty, said it was hoped the cards generate new leads by circulating crucial information about suspected victims among inmates who may have knowledge of those crimes.

"This format has already had success in the United States and other jurisdictions here in Australia, and we have worked collaboratively under Operation Veritas for almost two years to ensure we get it right," he said.

"We know inmates often share details of their crimes or those committed by associates with others; this is about capitalising on that and generating new information to progress these cases.

"Veritas is the Roman goddess of truth, and these cards are about the continued quest for answers and justice for the families involved."

Anyone with information that may assist Unsolved Homicide Unit investigators is urged to contact Crime Stoppers: 1800 333 000 or https://nsw.crimestoppers.com.au where information is treated in strict confidence - not via NSW Police social media pages.

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