A former detective Sergeant with the Sunshine Coast Criminal Investigation Branch, Mr Schmidt, who worked in Ethical Standards before retiring as a detective Inspector at Caboolture, was one of two arresting officers who helped put Paul Stephen Osborne away for life.

On the afternoon of October 29, 1995, two young girls, Leanne Oliver, 10, and Patricia Leedie, 9, of Ilaroo Crescent, Warana, had been out doorknocking looking for odd jobs to earn pocket money.

Osborne, a 27-year-old labourer and factory hand from Wurtulla, had been drinking and smoking marijuana at a workmate's barbecue which Leanne's father, Alby, had also briefly attended.

Osborne took off to the beach and witnesses had seen the two girls and Mr Osborne at the beach about 5pm, before they were reported missing.

A desperate, all-night search for the girls ended when Mr Oliver found their bodies in the sand dunes, only 500m from home.

Warwick Inspector Brian Cannon was acting officer in charge of the Sunshine Coast CIB at the time.

He remembered the call at home the night the girls had gone missing and the call he feared 12 hours later, confirming their bodies had been found.

"We had people volunteering on days off to come in and from afield," Insp Cannon said.

"It certainly took its toll on a lot of staff.

"It was a fairly emotive time (for police and the community), a number of investigators had young children around the same age."

Mr Schmidt and Senior Sergeant Mick Dwyer were two of those investigators.

As forensic evidence mounted up, Osborne's wallet was found by searchers in the dunes and the investigation quickly focused on the labourer, who'd already served time in jail for a sexual attack on a teen.

"No one likes to work on deaths of children," Mr Schmidt said.

Dozens of detectives had joined the initial search for what started as a missing persons case.

"There was always hope," Mr Schmidt said.

"Until it was confirmed (it was treated as a missing persons case) but in the background we were always preparing (for the worst)."

Police figures called the crime one of the most heinous they'd seen at the time.

"We were in the process of interviewing everyone there (at the work party barbecue) when searchers in the sand dunes found the wallet," Mr Schmidt said.

In 1985 Osborne had left personal papers at the scene in Brisbane after he'd sexually attacked and tried to strangle an 18-year-old woman.

Osborne had served three years and 10 months of a six-year prison sentence for the attack.

Mr Schmidt recalled how the wallet had helped in terms of speeding up the investigation, but he said they would've caught Osborne anyway.

"We had forensic evidence coming out of our ears," Mr Schmidt said.

"The girls were clubbed with a tree branch and sexually assaulted.

"It (evidence against Osborne) was obviously overwhelming and he blurted out his first admissions (after hours of interviews)."

Osborne was charged with two counts of murder by the evening their bodies were found and two counts of rape were later added.

Mr Schmidt said one of the challenges was that investigators only ever heard Osborne's version of what happened.

He said Osborne had told detectives he'd planned to run home along the beach from the party.

He said the two girls who recognised him from the party and they'd wanted to take him into the dunes to show him their cubby house.

Osborne then blamed a cocktail of drugs and alcohol for what happened next.

"Don't even know why it happened, and er, just sort of come to with the blood all over me," Osborne said in a transcript of a police interview.

Mr Schmidt said Osborne admitted he'd taken off into the surf after realising what he'd done and ditched his blood-covered shirt in the ocean.

Over the next 7-8 days Mr Schmidt and Sen-Sgt Dwyer checked the shoreline every day, searching for the shirt, which was eventually found by a government worker where it washed ashore at Dicky Beach.

The shirt was still covered in forensic evidence.

Over the next 4-6 months Mr Schmidt and Sen-Sgt Dwyer put together the brief of evidence.

There were hundreds of statements and thousands of pieces of evidence.

The work had to be meticulous to make sure Osborne did not avoid jail.

"Any half decent detective will look at a court case from a defence point of view and try and reinforce it... to put up a rock solid brief of evidence," Mr Schmidt said.

The motivation to put a child killer away was all they needed.

"It's a great feeling (to get a conviction), absolutely great," Mr Schmidt said.

"There's no better feeling than when the watch house door shuts on them (and the guilty verdict is read out).

"He got double life (for the murders), 18 years each (for the rapes), and was marked 'never to be released'.

"I hope those recommendations come into consideration. In my opinion jail's too good for him really.

"I hope he never gets released. He doesn't deserve to be out in public."

Despite the result, Mr Schmidt said the outcome was still devastating, with two innocent young girls murdered and their families' lives changed forever.

He said the girls sprung to mind every time he walked down the beach from Oceanic Drive.

"It was tough, it was taxing at the time," he said.

"At the end of the day we didn't leave any stone unturned. We couldn't afford to.

"On the day of the trial he stood up and pleaded guilty. It still doesn't change the outcome. You never really forget about it."

Mr Schmidt remembered digging his heels in while on holiday, when crown prosecutors were ringing him hoping to do plea bargains.

Osborne's defence counsel were offering deals like a guilty plea to one murder and one rape, or one murder and not the other.

"I just refused flat out, I said it's all or nothing," Mr Schmidt said.

"We were there from early in the morning to years later when he went to court.

"You've got to try and swallow your feelings. If you don't, you can bugger up a trial."

Mr Schmidt left the police service about four months ago to help out with his wife's business in Caloundra.

"It's nice to work with people that want to talk to you," he said.

The community outrage at the girls' murders struck Mr Schmidt.

He recalled a couple of thousands people outside the Maroochydore courthouse the day after Osborne's arrest.

"It was good to see so much public reaction to it," he said.

Insp Cannon praised the efforts of the search team, which was able to help narrow the investigation quickly.

"We had started with an open book basically," he said.

"Some good work at the crime scene produced some evidence very quickly."

He said the public's willingness to help catch the killer had helped spur the investigation on.

"The police can do a job, but without the public it becomes tenfold more difficult," he said.

"We were running briefings almost every hour (it felt like)."

He remembered how challenging it had been to select Mr Schmidt and Sen-Sgt Dwyer as arresting officers who would put together the brief, as they were both fathers themselves.

Insp Cannon said the case had touched nearly all who worked on it.

"It was fairly difficult for a few of the troops," he said.

Osborne remains an inmate at high-security Wolston Correctional Centre in Wacol.