Rex Wallman still has vivid memories of the day his sister went missing, and four decades on, it continues to haunt him.
Rex and his brother David were on the way to the school bus stop in the Mackay suburb of Eimeo. Their 14-year-old sister Marilyn was 10 minutes ahead of them.
When the boys, aged 8 and 11, caught up, she was nowhere to be seen. Instead, all they could find was Marilyn's bike on the side of the road and her half-opened schoolbag.
"We initially had a bit of a look around and yelled out but couldn't find her, so David rode his bike back home to get mum and dad," Mr Wallman said.
"I stayed on the roadside and I remember hearing noises in from far away in the cane paddock, but when we all went to search we couldn't find anything."
If Marilyn Wallman was still alive, she would have turned 60 on March 6.
Her disappearance on March 21, 1972, remains Queensland's longest-running child abduction case.
Over the years there have been clues — including the discovery of Marilyn's skull fragments in a tip and the sighting of a mystery vehicle — but police have never laid any charges.
"It was pretty traumatic … it's like it just happened yesterday," Mr Wallman said.
"Mum needed medication because she was so distraught and Dad was out every day searching."
The death of Mr Wallman's uncle last year has brought home the reality that secrets surrounding his sister's disappearance could go to the grave.
"Mum and Dad turn 82 this year and we don't know how much longer we will have them with us," he said.
There is currently a $250,000 reward for information that leads to Marilyn's killer, and Mr Wallman believes increasing that could help.
"The more publicity and the more people know there is a reward for information the better," he said.
"It would be nice to have a $1 million tag on there, but we don't have control over that — the Queensland Government do — so if the Premier is listening, we need it increased."
The ABC has contacted Queensland's Police and Justice Ministers for comment.
'Someone out there knows something'
In 2015 there was a breakthrough in the case, when years of forensic testing confirmed a piece of skull, found at an old privately used dump in McGregor Creek, belonged to Marilyn.
A year later police and geologists conducted scientific testing of the area to see if excavation was possible and to determine how much the landscape had changed.
Mr Wallman said while the initial search of the dump found no further remains, it was hoped the site could be more extensively excavated in the future.
"We're always hopeful that we can go back and do a more comprehensive dig, but we're waiting on confirmation from police and soil scientists to say if it is actually possible because it might not be worthwhile," he said.
Then there is the two-tone, aqua-white Holden sedan that was seen on the road where Marilyn went missing.
Detective Senior Constable Cindy Searle said it remained a "significant" part of the investigation.
"We have some people come forward with information of people they believe may have had vehicles similar to that in 1972 and that is useful to us, we do investigate all of those leads and talk to people we can locate for that information," she said.
School friends determined to find justice
On Saturday, Marilyn's family and friends reunited to celebrate what would have been her 60th birthday.
Marilyn's disappearance had a profound impact on her school friends, who were in Year 9 at North Mackay High School at the time.
Every year, her classmates organise a reunion to share stories about Marilyn with her family and each other.
Friend Trudy Voltz said it was "mixed emotions when we all get together, because we do wish Marilyn was here".
"We wonder what she would have be like," Ms Voltz said.
"She [Marilyn] was a lot of fun, her Dad has the same sense of humour that she use to have, and she was just a lovely, lovely person."
Kay Jenner said it was crucial they found out what happened to their friend and agreed the reward money for Marilyn's case needed to be increased.
"We have a common bond in that our classmate went missing and we still don't know what happened," Ms Jenner said.
"It's been over 45 years and we're all 60 this year — we're running out of time. We need answers and so do her parents."
Detective Senior Sergeant David Tucker said while the investigation into the case was ongoing, any information could be the missing piece of the puzzle.
"I am of the very strong belief that there is a person or persons here in our community that know exactly what happened to Marilyn Wallman, and I would encourage those people to come forward before it's too late," he said.
He said Marilyn's parents had worked tirelessly over the last 46 years to find out what happened and they deserved answers.
"They have lived every parent's nightmare, their child is missing, we know that Marilyn was killed, and they deserve to know what happened to their daughter," Detective Senior Sergeant Tucker said.