The ACT Supreme Court in 2020 sentenced Jason Pikula-Carroll to jail after he pleaded guilty to jointly committing six offences, including murder, with co-offenders during two violent invasions of artist Eden Waugh's unit in late 2016.

The offending was triggered after Pikula-Carroll, in his mid 20s, became upset with Mr Waugh, his drug dealer, about a failed heroin transaction involving an associate.

He took a shotgun and two armed co-offenders, Peter Forster-Jones and Phouthakone Sikounnabouth, to Mr Waugh's Watson unit where they badly injured him and others while demanding drugs and cash.

Six weeks later, the trio went back to try to stop him cooperating with police as they investigated the first incident.

Mr Waugh had barricaded the entrance, prompting Forster-Jones to fire the shotgun through the front door, killing him.

Among the things the offenders stole was a phone that was still connected to a triple zero call as they fled.

Forster-Jones described having "killed a c---" to which Pikula-Carroll replied with "I know".

The former on appeal had his sentence reduced from 40 to 30 years. Both were each given a non-parole period of 18 years.

MORE COURT NEWS

Pikula-Carroll's case came before the ACT Court of Appeal on Wednesday when his lawyer, John Purnell SC, argued that the sentence was manifestly excessive as his client's moral culpability was less than Forster-Jones'.

"Forster-Jones carried far more acts of violence than the appellant," Mr Purnell said.

He said the sentencing judge, Justice John Burns, should have placed more weight on his client's remorse and personal circumstances.

He said it was a non-sequitur to conclude that Pikula-Carroll knew the gun was loaded against evidence, including the triple zero recording, to suggest otherwise.

"It's a shot in the dark for a sentencing judge to find that the triple zero call could be used to come to the conclusion beyond reasonable doubt that the appellant knew the gun was loaded and that it did not indicate he was highly intoxicated, which was his contradictory evidence," Mr Purnell said.

The respondent, Katie McCann representing the ACT DPP, said the court should dismiss the appeal because Pikula-Carroll had pleaded guilty on the basis that it was a reckless joint offence and there was little difference between their moral culpabilities.

"The appellant was an active and willing participant in a joint criminal enterprise ... while he may not have pulled the trigger, when you look at it globally, there is very little difference," she said.

Ms McCann said the appellant also knew that Foster-Jones had a 12 gauge shotgun as the former had sourced it and it was used in the first home invasion.

She said the triple zero call played to the court was clear that both offenders knew the victim was inside at the door.

"At no point do you hear any surprise of either [the offenders] at all in relation to the fact that a gun had been discharged and to the fact that there was a deceased person on the floor," she said.

Ms McCann said the appellant's mental health issues and his crimes had no causal connection and that the weight upon which Justice Burns placed on remorse was "entirely a matter for him".

The appeal court has reserved its decision.

Our journalists work hard to provide local, up-to-date news to the community. This is how you can continue to access our trusted content: