A retired Mandurah detective says a $250,000 reward for information on a local cold case could unlock a 39-year-old mystery.
In 1999, Jeff Beaman reviewed the mysterious death of Mandurah teenager Annette Deverell, but failed to find the people responsible for her suspected murder.
On September 13, 1980, the 19-year-old Mandurah girl disappeared after a night out in town with her friends.
Her remains was found 18 months later in bushland near Pinjarra, about a 30 minute drive from where she was last seen.
In October, WA Police requested a reward be attached to Ms Deverell's case after the Mandurah Mail produced a four-part series on the largely forgotten case, putting it back in the spotlight.
Police have not confirmed the reward amount or when it will be announced.
Mr Beaman, who reviewed the case among his daily jobs for about six months, said he was not sure why the case had never received a substantial reward for information from the government.
"I'm probably guilty, I should have pushed for a reward when I was investigating it, but you're too focused on trying to get a result," he said.
"Maybe now it will happen."
More on Annette: Cold Case Unlocked:
Mr Beaman said a reward could encourage people sitting on information to come forward.
"There is a reward process if you help solve a crime, but it is subject to certain conditions," he said.
"If a substantial reward is announced, it will certainly give people an incentive to come out after 40 years.
"$250,000 is a life-changing amount, which could pay off their mortgage, or set them up for life."
Mr Beaman is convinced someone in Mandurah knows what happened to Ms Deverell.
"The person could be good friends or ex-friends with this person and they don't want to give them up out of loyalty," he said.
"There could be someone who played a minor part and they'e concerned about coming forward, but they might get leniency.
"This could be the opportunity to clear their conscience without going to jail."
Annette's mother Margaret Carver asked for a reward ahead of the podcast series.
Annette's brother Michael "Digger" Deverell said it would have to be a substantial amount for someone to speak after so many years.
In September, Mandurah MP David Templeman said a reward should be issued as a "matter of urgency".
If you have any information that could help police solve this case, contact Crime Stoppers on 1800 333 000. You can contact Carla Hildebrandt by emailing email@example.com.