Reward For 46-Year-Old Cold Case Of Murdered School Girl Doubled

"Justice doesn't have a use-by date."

Marilyn Wallman was just 14-years-old when she was last seen riding her bike towards school in Mackay, Queensland.

She was just ten minutes ahead of her younger brothers, who would later find her discarded bike on the side of the road, with no trace of their sister and no clue as to how or why she went missing.

That was 46 years ago, and to this day her killer has not been found.

Now, Queensland police are doubling their offer of reward to half a million dollars, to help bring those responsible to justice.

It's the first time in Queensland history an award to help solve a murder has been increased, after decades of campaigning from Marilyn's family -- who are still looking for closure.

Police Minister Mark Ryan said justice  "doesn't have a use-by date" and Police will continue searching for answers.

What happened to Marilyn

Marilyn's disappearance on March 21, 1972 sparked a massive police and community search, but little is known of exactly what happened to the young teenager.

Two years after her disappearance, in 1974 a skull fragment was found, but it took until 2015 for testing to reveal it was Marilyn's.

Police continue to believe she was murdered and say that a review of the cold case over the last four years following various people coming forward, led them to the "extraordinary" step of boosting the reward for her murder.

Marilyn's bike was found discarded.

"She was a 14-year-old girl. That tugs at the heart of Queensland and certainly the Mackay community,"  Detective Inspector Damian Hansen said.

No one has been arrested or charged over the incident but police confirmed on Tuesday that they have identified a person of interest.

"If that person of interest is listening today I ask [them] to come forward," Ryan said.

Reward boosted for 12 months only

The doubled reward is only available for a 12 month period and police say the decision to set a time limit is to give added incentive for anyone with information to come forward after such a long time.

"It's 46 years since this crime has been committed," Hansen said.

"People aren't getting younger and we seek them to come forward and listen to their conscience," Hansen said.

"We have a  person of interest and they are not getting younger either."

Hansen said over time the person responsible may have told someone and police now believe one one or more people could have information that could lead to Marilyn's killer.

"Loyalties deteriorate over that time, marriages breakup, and people do talk," Hansen said.

"Who they were loyal to 46 years ago may not be who they're loyal to now. I just ask them to listen to their conscience."

"It's a 14-year-old girl. Come forward."

Anyone with information is urged to contact Crime Stoppers on 1800 333 000. 

Contact the author: vgerova@networkten.com.au