Fort Nelson: Canadian authorities have confirmed Australian Lucas Fowler and his American girlfriend Chynna Deese were shot dead not far from their vehicle on the side of the Alaska Highway in the Northern Rockies.

Police went public with leads on Tuesday, hoping to prompt more witnesses to come forward. They released CCTV of the couple at a petrol station and a sketch of a man they want to speak to.

A screen grab from supplied CCTV footage released by Royal Canadian Mounted Police of murdered Australian man Lucas Fowler and his American partner Chynna Deese stopping at a petrol station in Fort Nelson. Credit:RCMP/AP

The footage shows the young couple pulling in at a service station in Fort Nelson, British Columbia at 7.30pm on July 13. Mr Fowler is driving the blue Chevrolet van he bought from a cattle ranch where he had been working. He had fixed it up especially for the road trip he had been planning with Ms Deese.

The footage shows the couple getting out – Mr Fowler fills the vehicle up with petrol while Ms Deese cleans the van’s windows. They embrace in a hug while filling up, looking happy and relaxed. The pair then head into the service station, use the bathrooms, grab some snacks then leave together.