An accused killer was suffering from a mental illness when he allegedly ran a pedestrian over at Prospect Vale in March last year, a jury has heard.
Joshua Josef Barker, of Kings Meadows, has pleaded not guilty to murdering Dale Watson during an alleged hit-run on Knox Street and assaulting Timothy Bumford shortly after on York Street in Launceston.
Career medical officer Dr Edwin Elcock told the Launceston Supreme Court on Monday he observed, assessed and treated Mr Barker while he was on remand and interviewed him in February this year.
The court heard Mr Barker underwent rigorous testing to determine whether he was suffering from a mental disease at the time of the alleged incident, with his behaviour in the years and months leading up to the day in question, meeting the five foundation criteria for post-traumatic stress disorder
Dr Elcock said Mr Barker would've been able to understand the act of driving at a person on the day in question, but he wouldn't have known it was something he shouldn't do.
"He was in incredible emotional turmoil ... he couldn't have understood because he was so thought disordered," Dr Elcock said.
"I couldn't be convinced he was aware of what happened."
In 2009, Mr Barker was bashed by four men with blunt objects after confronting the group about throwing something at his car on Hughes Court at Prospect Vale.
The assault happened a street away from where Mr Watson was allegedly hit by the accused's Ford Ranger at a speed between 40km/h and 47km/h.
The jury was told Mr Barker had been suffering delusions, including believing the men who assaulted him shot his cat and were looking for him.
Dr Elcock said the accused was suffering an acute phase of PTSD on March 9 and it impacted his capacity to think clearly.
The 31-year-old had a paranoid view of the world and he tried to make sense of it through religion and numbers, the court was told.
Mr Barker might've seen a snake, his attackers, satan when he drove at Mr Watson, the jury was told, but it was also possible he saw nothing.
"He didn't see a person he shouldn't attack," Dr Elcock said.
It was also possible Mr Barker mentally returned to the night of the assault, thought he was seeing a fifth attacker and acted in response, the jury was told.
During his one-hour police interview, Mr Barker remembered details about almost everything he did on March 9 but the alleged hit-run.
Dr Elcock said PTSD affects memory and the lack of recall was genuine.
The trial before Justice Robert Pearce continues.