West Australian Nicolau Francisco Soares has pleaded not guilty to killing his mother Dr Delys Weston and stepfather Professor Gavin Mooney at their Mountain River property in December 2012.

Jurors in the double murder hearing of Mr Soares were yesterday shown a series of graphic photographs of his two alleged victims.

Forensic pathologist Christopher Lawrence, who performed autopsies on the couple, told the Supreme Court in Hobart that Dr Weston received at least eight blows to the head.

``A lot of these injuries are highly consistent with being hit with a claw hammer,'' Dr Lawrence said.

The jury heard one injury was to a part of the brain considered vital to life, with the impact probably killing Dr Weston instantly.

``This sort of injury is the sort of injury I'd associate with the person not living after being struck,'' the witness said.

Dr Lawrence told the jury he identified at least 13 separate impacts to Professor Mooney's head.

He said at least one injury appeared to have been caused by a block splitter.

``It damaged the skull, it damaged the brain underlying it, it would have caused death,'' Dr Lawrence said.

The court heard both victims received a number of defensive injuries.

The jury was also shown a video walk-through of the crime.

On Monday, defence lawyer Rochelle Mainwaring told the jury Mr Soares was being treated for schizophrenia, and that the mental illness was acutely active when he attacked the couple.

Ms Mainwaring said her client was so mentally unwell he could not determine right from wrong at the time of the killings.

The trial continues today.