Expert evidence in trial of Bruce Anthony Coss, accused of murdering Darren Royce Willis in Bingara in 2010

Bruce Anthony Coss has denied killing Darren Royce Willis in Bingara in 2010, and his barrister Michael King called one defence witness in the NSW Supreme Court in Sydney on Thursday.

Professor Soren Blau told the court it was possible to observe some defects in four skull fragments found last year, but variables made interpreting the nature of them complicated.

"Given the relatively poor preservation, then we can say some things, but the extent to which we can go is limited," she said.

She said it was also made difficult by having an incomplete skull to work with.

She disagreed with some opinions the Crown's expert witness had given.

Professor Blau gave evidence that it was "very difficult, if not impossible" to work out sequencing of damage to the skull.

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During cross-examination, Crown prosecutor Liam Shaw asked if it could be ruled out that there was a blunt force trauma to the left side of the head.

Professor Blau said it was possible it "had impact".

The Crown case is that the bone fragments belong to 45-year-old Mr Willis, who Coss is accused of bludgeoning with a baseball bat in the street their homes were on.

The defence case wrapped up on Thursday and the judge-alone trial will continue on Friday.

It resumed this week after being suspended last year when new evidence - including the bone fragments - was discovered.

Coss has pleaded not guilty to murder. He was arrested after a fresh investigation in 2019.

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