Joshua Josef Barker, of Kings Meadows, has pleaded not guilty to murdering Dale James Watson and assaulting Timothy John Bumford on March 9, 2018.

The court heard Mr Watson was walking on Knox Street at Prospect Vale when he was hit and killed by the black Ford Ranger Joshua was driving.

Joshua allegedly revved his engine when he saw Mr Watson, mounted the kerb and hit him.

Crown prosecutor Linda Mason told the jury the force caused Mr Watson to hit the bonnet and be catapulted onto the road.

The impact of Mr Watson's head on the road caused catastrophic injuries, Ms Mason said.

Shortly after the alleged hit and run, Joshua is accused of assaulting Fastway courier driver Timothy Bumford near Sacred Heart Primary School on York Street in Launceston.

Joshua suffered with post traumatic stress disorder after being assaulted by four men armed with blunt objects at Prospect Vale in 2009, the jury was told.

The Kings Meadows man sustained two large lacerations - including one to the forehead that was bone deep - he lost consciousness twice, had abrasions on both knees, and tenderness to his right ribs and right thumb.

The alleged hit and run happened in very close proximity to where Joshua was attacked, the court was told.

The jury will hear evidence about Joshua's behaviour in the months and hours leading up to the alleged incident.

Defence lawyer Evan Hughes told the court Joshua's mental illness was echoing in his mind at the time, before cascading into a loss of understanding.

Mr Hughes said Joshua's family tried to assist with his illness and problems, but they struggled.

A statutory declaration by Joshua's father Peter was read to the court by Crown prosecutor Peter Sherriff.

The father detailed a number of recent events which heightened his son's mental health issues in the lead up to March 9, including his beloved cat being run over, his aunt having health issues, a friend's younger brother dying and a meltdown at work.

On the day of the alleged murder, Peter was driving when he heard about the alleged incident on the radio.

The car described was similar to Joshua's car, so Peter decided to drive to his daughter's house.

He called her on the way there and she told him Joshua had just pulled in to her driveway.

When he got to his daughter's house, Peter saw a dent in his son's normally immaculate car. Joshua denied hitting anything when questioned by his father.

Peter told police his son was white in colour and didn't seem to be registering what was said.

A jury panel of seven men and five women were selected, with two reserve jurors also empaneled at the request of Justice Robert Pearce.

The trial continues.