THE lawyer for an Australian mechanic accused of murdering backpacker Peter Falconio on a lonely Outback highway today began summing up his case by questioning the prosecutors' version of the attack.

Bradley John Murdoch, 47, faces a possible life sentence if the Northern Territory Supreme Court, sitting in Darwin, convicts him of murdering Mr Falconio, of Hepworth, on the Stuart Highway in central Australia in July 2001.

He is also charged with abducting and assaulting Mr Falconio's girlfriend, Joanne Lees, formerly of Almondbury and now living in Brighton.

Murdoch has pleaded not guilty to all charges.

Prosecutors say Murdoch shot 28-year-old Mr Falconio and then hid his body after flagging down the couple's camper van.

Neither Mr Falconio's body nor a murder weapon has been found, despite extensive searches by police and Aboriginal trackers.

Murdoch's lawyer Grant Algie said a number of aspects of the prosecution case were strange and could cause doubts in the minds of the 12 jurors.

Prosecutors contend that after killing Mr Falconio, Murdoch probably took the body in his pick-up truck and dumped it in the desert. A pool of Mr Falconio's blood was found on the roadside where the murder allegedly took place.

Mr Algie said it was strange no human blood was found on the backpackers' camper van, behind which Mr Falconio was allegedly standing when he was shot.

"Why would you possibly pick up a dead body, complete with blood, and put it in your car," asked Mr Algie. "You would have to be nuts."

Prosecutors are expected to sum up their evidence later this week before the jury retires.

They are relying largely on evidence that DNA, allegedly matching or consistent with Murdoch's profile, was found on the back of Miss Lees's T-shirt, the camper van's gearshift and the cables used to tie her wrists.

Mr Algie also suggested there was something "strange" about the handcuffs, which were made of cable ties and duct tape with three central loops, that were used to bind Miss Lees's hands behind her back during the attack.

"What's the point of these somewhat elaborate handcuffs?"

"If you've got cable ties and you want to handcuff someone, don't you just grab their hands and tie them together?"

Mr Algie also pointed to the three marks found in the scrub, which were said to be footprints, adding they did not belong to Miss Lees nor to any of Murdoch's eight pairs of shoes.

Later, he attacked the credibility of the prosecution witnesses.

The court heard how David Stagg, an Alice Springs art teacher, originally told officers Miss Lees said she was in her attacker's vehicle when she moved her hands from her back to her front, but later changed his story.

Mr Algie said: "At one point they seem to be saying one thing and then subsequently, particularly in the trial here, they seem to be distancing themselves from it. And you might think Miss Lees is another example of saying one thing at one point and now distancing herself from it.

"Why is there a change in story?"

He also questioned why Miss Lees did not see her boyfriend's body when she was taken from the camper van to her attacker's vehicle, and why she did not smell anything when the gun was poked at her temple.

But Mr Algie said if the jury was convinced something did happen that night, they would then need to consider what evidence there was that the person involved was Murdoch.

He said the prosecution's case was based on two unsupported assumptions - that the blood on Miss Lees's T-shirt came from her attacker and that the man caught on security cameras at the Shell service station in Alice Springs was the attacker.

"It's just a guy at a truck stop with a four-wheel drive similar to those owned by thousands of other people - just an indistinct guy at a truck stop."

He said Murdoch's DNA could have been transferred, either directly or indirectly, on to Miss Lees's T-shirt earlier that day in Alice Springs, rather than during the attack.

He gave the example that Miss Lees and Murdoch could have passed in a doorway without realising it.

Mr Algie told the jury Miss Lees had originally identified Murdoch from a police photoboard during an interview in the UK after having seen his picture on the BBC News website.

He said once Miss Lees had seen Murdoch's image on the website, from that point onwards she was identifying Murdoch, rather than her attacker.

Mr Algie also attacked the evidence of Dr Jonathan Whitaker, of the UK's Forensic Science Service, who used a relatively new "low copy number" DNA technique to show DNA found on the handcuffs was 100m times more likely to have come from Murdoch than anybody else.

Mr Algie told the jury: "Perhaps some explanation or acknowledgement that he could be wrong might have been more reassuring than a pronouncement that he's the expert and therefore you should accept it."

He also attacked the evidence of Murdoch's former business partner, James Hepi, who said he saw Murdoch making handcuffs in Sedan, South Australia. He suggested the story was "complete rubbish" as the pair had argued over their drugs trade and Mr Hepi believed Murdoch was to blame for him being charged with a serious cannabis offence in May 2002.

Talking about other DNA tests carried out in Darwin, Mr Algie said Dr Peter Thatcher's DNA was found on the handcuffs allegedly used on Miss Lees.

Mr Algie said: "What confidence do you have in a laboratory that ends up having its director's DNA all over the handcuffs?" Later he suggested Murdoch could have been "set up".

Referring to Murdoch's DNA which was found on these handcuffs, Mr Algie said: "Could they have been contaminated intentionally?"