The man accused of killing Briton Peter Falconio has a different build to a man captured on CCTV hours after the 2001 attack, an Australian court has heard.
Mr Murdoch denied killing Peter Falconio under cross-examination
Body structure expert Professor Maciej Henneberg also told the Darwin court the CCTV images from an Alice Springs truck stop were of "very poor quality".
Another defence expert also raised "concerns" about some DNA evidence.
Bradley Murdoch, 47, denies murdering Mr Falconio and kidnapping and attacking his girlfriend Joanne Lees.
Prof Henneberg, the head of anatomical science at the University of Adelaide, said on Thursday he had compared the CCTV footage with pictures of the defendant taken between 1995 and 2005.
Asked by the defence what his assessment of the images was, he told the Northern Territory Supreme Court the images showed a man of a particular body build.
He assessed this to be a lean body build, and with a body size of medium to medium large, but not excessively large.
"What I could tell was that the person of interest in the CCTV image and Mr Murdoch differed in their body build and probably in their overall size and stature."
Mr Murdoch is around 6ft 5in, the court heard.
Prof Henneberg, an expert in variations in human body structure and a visiting fellow at Oxford University, said he disagreed with earlier evidence by forensic expert Dr Meiya Sutisno.
She had told the court Mr Murdoch shared several distinctive face and body characteristics with the man captured on the video footage.
Joanne Lees and Peter Falconio were travelling across Australia
They shared features including sloping shoulders, long torso, jaw, chin and walking manner, she had said.
But Prof Henneberg cast doubt on Dr Sutisno's conclusions and also accused her of using several scientific terms incorrectly during her evidence.
"It's impossible, except where there is some peculiar disfiguration or anatomical anomaly, to reach 100% certainty in comparisons of images which are not very good quality."
However, during cross-examination by Rex Wild, QC, the director of public prosecutors, the professor admitted Dr Sutisno carried out further enhancement of the images which he had not undertaken.
"She uses the same basic principles of comparing images feature by feature, so to that extent that's the same procedure.
"I used the original images. I never manipulate images that I receive."
But he admitted that Dr Sutisno had different methods and could "see more".
On Wednesday, the court heard Mr Murdoch say even his own father had thought he looked like the man pictured on CCTV.
On Thursday, doubt was also cast on DNA evidence the prosecution had presented claiming a sample on the handcuffs used to tie up Miss Lees was 100 million times more likely to come from the defendant than anyone else.
Dr Katrin Both, part-time forensic scientists at the Forensic Science Service in Adelaide, said she had a "large number of concerns" about the tests used.
The method was "very dangerous" and pushed "science to the limits", she said.
Miss Lees, of Brighton, Sussex, has told the court she and Mr Falconio were flagged down by Mr Murdoch while they were driving across the Outback.
He is then alleged to have shot Mr Falconio, of Huddersfield, West Yorkshire, and bundled his girlfriend into the back of his van, before she escaped and hid in the undergrowth.
Mr Murdoch has denied this under cross-examination.
The trial continues.