DEFENCE lawyers today sought to discredit evidence that Bradley John Murdoch was the man in a security film made soon after backpacker Peter Falconio disappeared.

Forensic anatomist Meiya Sutisno told the Northern Territory Supreme Court that Murdoch, who is accused of murdering the 28-year-old, shared a number of distinctive face and body characteristics with the man in the video.

The man was filmed at an Alice Springs truck stop early on July 15, 2001 - just hours after Mr Falconio disappeared from beside the Stuart Highway, near Barrow Creek, about 180 miles (300 kilometres) from Alice Springs.

But defence lawyer Grant Algie today attacked Dr Sutisno's analysis, suggesting the film was of too poor a quality to make such a comparison.

He superimposed an image of another man over the footage, in a bid to show the quality of the footage was "wholly inadequate", and the interpretation "meaningless".

But Dr Sutisno, an expert in body and facial mapping, said there were marked differences between the two men, including the shape and size of the head, the chin and the ear position.

She told the Darwin court: "It seems to me it's a smaller person enlarged to fit this person."

Murdoch, 47, has pleaded not guilty to murder and to assaulting Mr Falconio's girlfriend, Joanne Lees, formerly of Almondbury, and depriving her of her liberty beside the Outback road in July, 2001.

She and Mr Falconio, from Hepworth, were touring Australia when the alleged ambush happened.

No trace of Mr Falconio has ever been found, despite one of Australia's biggest-ever police investigations.

Miss Lees says she managed to escape her attacker and hide in the bush for several hours before being rescued.

The trial continues.