In 2014, Adrian Wayne Smillie, of Devonport, was found guilty of stabbing Benjamin Maxwell to death and wounding Ashley Stott outside the pair’s apartment complex in Devonport.

The court heard that Smillie may have suspected his victims of being romantically involved with his partner.

Justice Stephen Estcourt imposed a non-parole period of 12 years on Smillie.

But, in 2016, the convicted killer launched an appeal against his sentence in a bid to quash the original conviction and prompt a new trial.

Smillie asserts that Mr Maxwell attacked him with a knife and thus he acted in self-defence on the day of the killing.

His counsel Kim Baumeler is arguing that Justice Estcourt erred in his direction to the jury concerning the standard of proof.

On Wednesday, Ms Baumeler asserted that the trial judge in Smillie’s case had made an error when he elaborated on the concept of reasonable doubt in addressing the jury.

She suggested it introduced a greater margin for error in the jury’s deliberations, compromising the accused’s right to be given the benefit of the doubt.

Crown prosecutor Tony Jacobs, meanwhile, said that the defence’s case amounted to arguing “semantics”.

“To tell a jury that they must test [reasonable doubt] is getting at the essence of their duty,” Mr Jacobs said.

The court will consider submissions before making its judgment.