The talented snowboarder had just returned from competing in Canada when tragedy struck.

On April 18, 2000, the 20-year-old went for a walk and never made it home.

MORE CHAPTERS IN FIVE-PART SERIES:

HUNT FOR FROGMEN WHO KILLED RUSSIAN MILLIONAIRE SPY

WHY WAS SAUDI ROYAL BURNED AND DUMPING IN HINTERLAND?

WHO KILLED COLIN WOODHOUSE?

COUPLE KILLED IN FRENZIED STAB ATTACK

His mother reported him missing and conducted a massive campaign to find her son.

Three weeks later police found his badly decomposing body in bushland near a water tower.

Mr Milligan was wearing one sock and one shoe and some of his clothing was found burnt nearby.

Police have treated the death as a murder investigation, but lead investigator, Detective Senior Sergeant Mark Procter, said there had been no fresh leads for some time.

“I have been on this case since the beginning and it has never been an easy one,” the Coomera CIB boss said.

“A bushwalker found clothing of his not far from his house, so we went there to look and that’s where we found his body.

“It was so badly decomposed there was no official cause of death, which always made the investigation hard.

“There was suggestion his clothes had been cut from his body, and we did find cuts in them.

“We stay in touch with his mum from time to time, who still lives in Oxenford, but at this stage we can’t rule anything out when it comes to the investigation.”

Det Snr Sgt Procter said the last “break” police had in the case was a few years ago when a distant relative came forward, but the information provided turned out to be incorrect.

“There were reports at the time that it may have been a drug deal or debt gone wrong, but we found no evidence of that,” he said.

“He was a champion snowboarder with plans to travel to Perisher for the Australian winter. What happened is still a mystery.”

Det Snr Sgt Procter said six months after Mr Milligan’s body was found his car keys turned up in a hanging pot plant at his family home.

“His keys were found there and no one knew he put them there. It could be he left them there while he went walking.”

Mr Milligan’s mother, Debbie Barrow, told media in 2014 that not knowing what happened to her son was both a blessing and a curse.

“In some ways I have come to terms with not knowing,” she said.

“Whereas, if I were to learn a horrible truth, I could be let down.

“I’ve had 20 million different scenarios go through my head but there’s no hard, cold facts.”

Ms Barrow said she believed her son could have simply have been in the wrong place at the wrong time, the victim of an impulsive action rather than cold-blooded murder.

A reward for $250,000 is still available for anyone with information that leads to the apprehension and conviction of the person or persons responsible for the suspected murder.

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