The killer of Karen Edwards, 23, Tim Thomson, 31, and Gordon Twaddle, 21, could soon be brought to justice as detectives trawl through old files and track down new and old witnesses.

The mystery is examined in a four-part podcast after The Courier-Mail spent months speaking with family, retired police and other relevant people about the case.

The three friends are believed to have been lured into remote bushland near Mount Isa and executed just days into a motorcycle trip through outback Australia and down the east coast.

All three had been shot in the head with a .22 rifle. One of the men had tried to run, his body found nearly 100m from the others. They had been stripped of identification and had their jewellery removed.

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Karen and Tim, who were in a relationship, were travelling on a valuable and eye-catching BMW motorbike with a homemade sidecar that carried camping gear and Tim’s doberman pup Tristie.

With them was Gordon, a family friend of Tim’s from New Zealand — also a motorbike enthusiast.

The three friends, from Melbourne and NZ, met in Alice Springs on September 30, 1978, and set off on October 2 for an “adventure of a lifetime” around Australia.

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Their plans involved travelling through outback Northern Territory into Queensland and across to Cairns before travelling down the east coast, finally arriving in Melbourne in time for Christmas.

They were last seen on October 5 at Mount Isa’s Lake Moondarra Caravan Park before their badly decomposed bodies were discovered in bushland at nearby Spear Creek on October 24.

Days later, police were badly hurt in a helicopter crash as they surveyed the crime scene from the air.

But soon, witnesses emerged with descriptions of a bearded man who joined the trio on their travels.

It is believed the man, who possibly had a motorbike and a Toyota LandCruiser, lured Karen, Tim and Gordon into the bush, perhaps with an offer to show them around.

Two weeks into the investigation, police arrested Bruce John Preston, 22, and charged him with the theft of Tim’s BMW motorbike.

Preston was fined $300 after telling detectives he spotted two men trying to start the bike and told them he knew the owner. He wheeled it home, altered its appearance and hid it away.

“It is definitely solvable,” homicide detective Senior Sergeant Tara Kentwell said.

“The Cold Case Investigation Team and Mount Isa Criminal Investigation Branch are working collaboratively to achieve this.”

Police identified the bodies after finding a watch in thick spinifex near where Karen’s body was left.

Photographs of the watch and some of the victims’ clothing were circulated to the media. Karen’s father Jack, at his home in the Melbourne suburb of Dandenong, spotted his daughter’s watch in the newspaper and contacted police.

All three victims’ families spoke to The Courier-Mail about the cold case review and said they were hopeful of an arrest after so many years.

The parents of the victims have all died.

“I think my parents would have liked to know who did it,” Tim’s brother, Dr Ken Thomson, said.

“It’s not going to bring him back. But the thought that someone who’s done this terrible deed is still out there and possibly doing it again, they should be removed from society in some form.

“Just knowing (who did it) brings a certain closure to it. Otherwise, it’s just open.”

Ken described his brother Tim — a schoolteacher from a family of doctors and engineers — as a “lovely, kind, generous, outgoing” man who loved his dog and liked to collect and restore old motorbikes and cars.

Originally from NZ, he spent time in Adelaide and Melbourne before moving to Alice Springs.

He worked at the Hermannsburg Mission for two school terms teaching English to Aboriginal children to save for his fateful trip.

Tim was a friend of Gordon’s older brother John. John, who ran a motorbike repair shop in South Dunedin, NZ, met Tim when he brought him a Harley-Davidson racing bike to fix.

They became firm friends and would go on rallies and to race meets together, as well as doing lots of motorbike touring.

When Tim talked about doing a trip around Australia on his bike, John suggested his brother Gordon might be interested.

John described Gordon as a “cheeky young guy” who worked as a pastry cook. He was generous and funny.

John planned to meet them on the Gold Coast when the trio made their way to southeast Queensland.

Instead, he made the trip to Australia for a funeral.

“(An arrest) would be a relief,” he said.

“You always think, golly, was it someone that you might have known? Someone that might have been from here that was over there (in Australia) at the time?

“It’s something my brother and myself talk about every now and again … shall we go to Australia and try and do something about this?”

Karen was the eldest of five children — a feisty, independent and athletic woman who was studying in the hope of becoming a medical laboratory technician.

Her brother Barry said Karen still had a massive presence within their family.

“I think the experience is just as terrible as most people imagine,” he said of his sister’s murder. “The person who did it should come forward himself. I mean, I wonder what sort of life he must be leading.

“To have that with you for all these years. Must be terrible.”

Anyone with information on the murders should contact Crime Stoppers on 1800 333 000.