Canadian authorities have made the chilling declaration the shooting murders of Lucas Fowler and Chynna Deese could be linked to another grisly roadside murder.
Senior NSW police officer Stephen Fowler has addressed the media in Canada about the murder of his son.
"I may be an experienced police officer but I'm standing here as the father of the murder victim," Chief Inspector Fowler, of Sydney's north-west Hills district, told reporters.
"We're just distraught."
He said the pair were inseparable and described the events as "a love story that's ended tragically."
"It's the worst-ever love story," he said.
At a press conference, Canadian authorities told reporters the shooting murders of Lucas Fowler and Chynna Deese could be linked to another roadside murder.
The police said a bearded man driving a Jeep Cherokee could hold to key to solving the shooting murders of the Australian and his girlfriend and potentially another grisly murder.
The Royal Canadian Mounted Police released a sketch on Monday of the man who was seen by a passerby talking to Mr Fowler on a remote highway in northern British Columbia a week ago.
Mr Fowler, 23, from Sydney, and Ms Deese, 24, from North Carolina, were stranded on the highway after their blue 1986 Chevrolet van broke down on the afternoon of 14 July.
They were found dead in a ditch the next day.
The RCMP raised fears the couple may be victims of a murderous crime spree in northern BC by declaring it was possible the killings are linked to the discovery on Friday of another dead man, two missing teenagers and a torched Dodge pickup truck.
"It's possible," RCMP Corporal Chris Manseau told reporters.
"We have two complex and dynamic ongoing investigations that are happening in northern BC."
The man who was seen talking to Mr Fowler was described "as Caucasian with darker skin and dark hair".
"He's shorter than Lucas who stood six foot three (190cm) and has a possible beard or glasses," RCMP Sergeant Janelle Shoihet.
The RCMP originally played down speculation of a serial killer or crime spree linking the murders of Mr Fowler and Ms Deese to Friday's discovery 470km away of the body, missing teenagers and the burning Dodge pickup.
"We just know more about both incidents," said Corporal Manseau, explaining the alarming change.
The two missing teenagers are 19-year-old Kam McLeod and 18-year-old Bryer Schmegelsky from Port Alberni, BC.
The RMCP said Mr McLeod and Mr Schmegelsky were driving the Dodge pickup but have not been in contact with their family for the last few days.
Sgt Shoihet said investigators are not treating the teens as suspects but want them to contact authorities.
"We're hopeful they alive," Sgt Shoihet said.
The body found 2km from their pickup was not one of the teens, but a bearded man aged 50 to 60-years-old.
The RCMP have been unable to identify the dead man and also released his sketch.