Brain scans of accused killer Luigi Costa showed no abnormalities normally associated with dementia, a court has heard.
Subscribe now for unlimited access.
$0/
(min cost $0)
or signup to continue reading
The expert who diagnosed the Red Hill man with the brain disease admitted he would expect the scans to detect areas of atrophy.
Instead, the court heard an area of Costa's brain not associated with dementia showed signs of damage, but that could be explained by hypertension.
Costa, 71, is on trial in the ACT Supreme Court accused of murdering his neighbour, Terrence Freebody, on July 22, 2012.
About 5.30pm, police found Mr Freebody dead on the floor in a room of Costa's Mugga Way home.
The defendant was located in a toilet with the deceased's blood on his hands and a knife on a nearby sink.
Costa - who claims he has no memory of Mr Freebody's death - has pleaded not guilty on the grounds he suffers from a mental impairment, which his defence team says is dementia.
But prosecutor Shane Drumgold alleges the defendant is faking the degenerative disease to escape justice.
Mr Drumgold closed the prosecution case last week and the defence has called witnesses to support the defence of mental impairment.
On Tuesday, the trial heard from clinical psychologist Dr John McMahon, who diagnosed the accused killer with dementia.
Dr McMahon said he made the diagnosis based on Costa's performance in a series of brain function tests.
But he admitted scans of Costa's brain did not show damage to support the diagnosis.
Under cross-examination, Dr McMahon also admitted he had ignored checks embedded in the test - used to pick up malingering - in making his finding.
When questioned why, he said he did not trust the tests as they were new and had not yet been scrutinised by enough independent research.
He denied he had cherry picked results to support his diagnosis.
Psychologist Dr Pauline Langeluddecke cast doubt on the test results used, saying the diagnosis had been made using the wrong test, which had also been incorrectly conducted.
Dr Langeluddecke said Costa performed poorly in the embedded malingering tests.
But he performed well in difficult tasks, which was a conflicting result and could indicate he exaggerated his symptoms.
But forensic psychiatrist Dr Stephen Allnutt told the court he thought Costa suffered from mental impairment that went beyond intoxication at the time of the offence.
"He suffered from a disturbed mental state, secondary to an underlying dementia, aggravated by alcohol and possibly other medication," Dr Allnutt said on day four of the trial.
The trial will continue before Justice Helen Murrell on Wednesday.
