A forensic psychiatrist says a wealthy property owner who allegedly murdered his elderly neighbour suffers from dementia, a trial has heard.
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But another expert argues accused killer Luigi Costa may have faked brain function tests to exaggerate his symptoms of the disease.
His neighbour, Costa, 71, is on trial in the ACT Supreme Court accused of his murder.
He has pleaded not guilty.
The case hinges on whether Costa suffers from mental impairment.
Defence barrister Remy van de Wiel, QC, says his client has no memory of the alleged killing.
But prosecutor Shane Drumgold alleges Costa has feigned symptoms to escape prosecution for Mr Freebody's death.
The court has heard Costa and the Freebodys – who lived across from each other on Mugga Way – had been drinking together earlier in the afternoon.
Mr Freebody's widow left about 5pm after Costa repeatedly used foul language.
Costa called triple-zero for assistance soon after.
Police arrived about 5.30pm to find Mr Freebody dead and Costa in a nearby toilet, covered in faeces and blood on his hands, with a knife in the sink.
The evidence of forensic psychiatrist Dr Stephen Allnutt continued on day four of the trial on Friday.
From the witness box, Dr Allnutt – who visited Costa twice at the Alexander Maconochie Centre – had previously told the court Costa had reported recalling inviting the Freebody's over for a drink, putting on music, and then feeling under attack.
On Friday, Dr Allnutt said he believed Costa, at the time of the offence, suffered from mental impairment that went beyond intoxication.
"He suffered from a disturbed mental state, secondary to an underlying dementia, aggravated by alcohol and possibly other medication," Dr Allnutt said.
When asked about the prosecution's hypothesis that Costa had attempted to hide the body, Dr Allnutt said the accused had called the police which seemed contradictory.
Jurors also heard from psychologist Dr Pauline Langeluddecke who cast doubt on the test results used to make the dementia diagnosis
Dr Langeluddecke said the wrong test had been used to make the diagnosis, and the test had been incorrectly conducted.
She told jurors that the test included embedded checks to pick up malingering.
The doctor said Costa performed poorly in those tasks – worse than people who had undergone a temporal lobectomy – but he could complete difficult tasks.
Dr Langeluddecke said the results were conflicted and did not make sense.
The trial before Justice Helen Murrell will continue next Wednesday.
