Keith Lees, 70, was last seen in Portland, Victoria on Monday morning following a visit from detectives investigating the 1997 death of Meaghan Louise Rose.
His vehicle, a silver Holden Captiva, was located at Cape Nelson Lighthouse eight-and-a-half hours later with police immediately launching a search involving the Victorian force's Air Wing.
Originally ruled suicide, Ms Rose's death is the subject of a $500,000 reward for information about her murder announced by Queensland detectives on Tuesday.
The 25-year-old's body was discovered at the bottom of Point Cartwright Cliffs at Mooloolaba while her car was abandoned at the top of the cliff.
In 2009, the investigation was reopened but her murder remains unsolved.
Ms Rose had moved from Victoria to Queensland with Mr Lees, who was more than 20 years older than her. The couple moved to the Sunshine Coast with his young son.
Once there, a life insurance policy was taken out for Ms Rose containing a clause that it had to run for 13 months before coverage applied in the case of suicide.
She was found dead 13 months and three days later, with a $203,000 payout later claimed.
"We do believe that with public assistance, irrespective of the passage of time, this crime can be solved," Queensland Police Detective Senior Sergeant Tara Kentwell said on Tuesday.
"Offenders can be brought to justice and we can provide some closure to Megan's family and friends."
Ms Rose was one of four siblings - her father has since died and her mother suffers dementia.
"From day one, we never believed this was suicide," sister Fiona said.
"At the time of her death, just 25 years of age, she had bought her first car.
"She bought her first home and she moved interstate to a place where she always wanted to be."
Ms Rose told friends and family in the days before her death her relationship was over and she intended to leave.
For decades, they clung to the hope of justice, each holding a theory about what happened.
"We saw the difference in Megan in the 10 months that she had been up here ... her demeanour had changed," Fiona said.
"It's hard to explain because she was such a bubbly person. She was happy-go-lucky ... but she changed.
"It was like she couldn't talk sometimes."
Sgt Kentwell said witnesses would be re-interviewed as police appealed for the public to help.
Victorian police say Mr Lees is of medium build, about 170cm tall and has grey receding hair.
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