Despite his injuries Tylor Bell was able to drive to a nearby hospital, but he died a week later.

Alex Robert Smart admits inflicting the stab wounds, but pleaded not guilty to murdering the 31-year-old at the start of the Brisbane Supreme Court trial on Tuesday.

Prosecutor Dejana Kovac told the jury Mr Bell "hung around" outside the shopping centre in Gympie, north of Brisbane, on September 1, 2019 while his father Gregory Bell bought groceries.

As the pair left about 25 minutes later there was "a quick exchange" between Mr Bell and Smart, who was at the main entrance, before the murder-accused rushed towards their ute.

"He (Smart) then stopped rather abruptly and walked backwards just as the deceased stopped the car," Ms Kovac said.

She told the jury CCTV footage shows Mr Bell - holding what looks like a small metal implement - and his father getting out their ute.

Mr Bell walked towards Smart, but "never stood close to him even for one second" before the pair exchanged words for about 20 seconds.

While Mr Bell put the implement back in car, his father punched Smart once in the head with the murder-accused responding by kicking out which caused Gregory Bell to fall, Ms Kovac said.

Mr Bell ran to separate the men, but a struggle continued for 10 to 15 seconds until witnesses intervened and the father and son drove away.

About the same time a silver Holden in which Smart's girlfriend was a passenger pulled up at the entrance.

It sped away quickly after Smart got inside, but stopped next to the ute at a red traffic light.

Ms Kovac said witnesses saw Smart get out the car armed with a knife only seconds after hearing the men yelling.

He approached the driver's door of the ute, stabbing Mr Bell twice, with one wound so deep it penetrated his heart, she told the jury.

There was no time for the father and son to swap seats before the injured Mr Bell drove away.

"He somehow managed to drive to the hospital which was only a short distance away," Ms Kovac said.

But Mr Bell went into cardiac arrest and died in a Brisbane hospital a week later.

The Crown will argue an interview Smart gave to police and recorded conversations made in a watch-house cell by two undercover officers showed the "evolving nature of the versions he gives".

Defence barrister Jakub Lodziak said the trial was "not a whodunnit" because Smart had stabbed Mr Bell.

But Mr Lodziak said how and why that happened would be important questions for the jury to consider.

The trial before Justice Peter Applegarth is expected to hear from about 20 witnesses.

Australian Associated Press