Mystery Mounts Over Murdered Australian Lucas Fowler And Girlfriend

A group of tourists saw Lucas Fowler and Chynna Deese just a day before they were found dead, the young couple enjoying a picnic by their broken-down van before their murder.

Fowler, from Sydney, and his American girlfriend were found shot dead by the side of the Alaska Highway in British Columbia last Monday.

Canadian couple Curtis and Sandra Broughton were on their way back from a camping trip in the Yukon territory, in remote northwest Canada, when they came across the "happy and smiling" pair on Sunday afternoon.

Image: Facebook

The blue 1986 Chevrolet van Fowler and Deese had been travelling in had broken down on the highway, where they stopped to let it rest.

“They seemed like they kind of had it under control. It was mechanical issues with the van," Curtis told Canadian news outlet Global News.

"They were having a picnic waiting for the van to unflood, I guess, and try to start it again."

READ MORESenior NSW Cop's Son And Girlfriend Killed In 'Horrific Circumstances'

Witnesses said it appeared the couple's blue van had broken down. (Image: AAP)

The Broughtons said they offered Fowler and Deese food and water before leaving them in good spirits, about 20 kilometres south of Liard Hot Springs.

"I'm a mechanic and they explained the problem perfectly. I was impressed, so I was confident they were going to be on their way," Curtis said.

The next day, Fowler, 23, and Deese, 24, were found dead on the roadside. The pair were shot in what police said "can only be described as horrific circumstances".

The couple's bodies were found about 20km south of the Liard hot springs on British Columbia's Alaska Highway. Photo: Google

A manhunt remains underway as authorities fight back speculation a serial killer may be operating in the area.

Some media reporting has linked the double murder with the discovery of another body -- 470km away from where Fowler and Deese were found dead -- near a burning red and grey Dodge pick-up truck. However, police have repeatedly stressed they have no evidence the two deaths are connected.

The remains have not been identified, but the Dodge was driven by 19-year-old Kam McLeod and 18-year-old Bryer Schmegelsky from Port Alberni, British Columbia. Police confirmed on Monday neither McLeod or Schmegelsky have been found, and the pair have officially been listed as missing.

Royal Canadian Mounted Police have repeatedly fended off speculation a serial killer was on the loose and have not publicly linked the incidents, but on Sunday acknowledged "there are growing community concerns about the ongoing homicide investigations in northern BC".

"At this time, investigators are sharing information and police would like to ensure awareness around both investigations," RCMP spokesperson Dawn Roberts said.

"The RCMP would ask the public to continue to take any general safety precautions and remain vigilant at this time."

Lucas Fowler and Chynna Deese. Photo: Facebook

The Deese family has also said they do not believe their daughter's death is the work of a serial killer.

"I think of someone who has been convicted of violent crimes before, someone on drugs. That fits the profile better," Deese's father Dawyne told the Charlotte Observer.

"What worries us is that the person is still on the loose and they have a head start."

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Fowler's father, NSW Police Chief Inspector Stephen Fowler, has travelled to Canada to bring his son's body home.

He has been accompanied by two experienced NSW homicide detectives, who according to Canadian police are there to support the Fowler family and will not be aiding the investigation.

Fowler and Deese met backpacking in Croatia two years ago, fell in love and embarked on a Canadian road trip in the old Chevrolet.

With AAP.