But Jason Pikula-Carroll insists he "didn't even know what had happened", and that he was "just blurting out words" in fear of his co-offender.

Emotions ran high in the ACT Supreme Court on Wednesday as Pikula-Carroll faced a sentence hearing over two 2016 home invasions, the latter of which resulted in the death of Canberra artist Eden Waugh.

The 25-year-old has pleaded guilty to six charges, including murder by joint commission, admitting that he first broke into Mr Waugh's Watson unit in September 2016.

Giving evidence on Wednesday, he said he had been upset with the victim, who sold him drugs, over a deal gone wrong.

This prompted the former apprentice chef to collect a shotgun and enlist Peter Forster-Jones and Phouthakone Sikounnabouth to go with him to the home of 37-year-old Mr Waugh.

The trio, all armed, forced entry and collectively threatened and assaulted the occupants while demanding cash and drugs.

One man was so terrified he jumped out of a third-storey window to escape and fractured his spine.

Six weeks later, planning to steal more items and scare Mr Waugh in the process so he would not co-operate with a police investigation, the offenders returned.

Pikula-Carroll said he approached the unit with Forster-Jones, but they were unable to get in.

He told the court he was standing beside Forster-Jones when the latter fired a shotgun through the front door.

The bullet killed Mr Waugh, and when Pikula-Carroll entered the home with Forster-Jones to pillage the place of valuables, he grabbed Mr Waugh's partner Marion Barr by the hair and dragged her across the floor.

The pair did not realise as Sikounnabouth then drove them away that Ms Barr's phone, which they had stolen as they left her to cradle Mr Waugh's lifeless body, was still connected to a triple zero call.

In a recording played to the court, Forster-Jones could be heard saying "I f---en killed a c---, bro", and "I wasted him".

Pikula-Carroll replied "I know" and repeatedly told Forster-Jones "you're a gangster", before yelling "woooooooo".

Crown prosecutor Anthony Williamson said this "cheering and yahooing" was damning to Pikula-Carroll's claims that he was haunted by the incident and that he had not known the gun was loaded until it was fired.

But Pikula-Carroll argued he had been scared of Forster-Jones, which was why he did not remonstrate with him.

He cried in court as he read an apology to Mr Waugh's family, describing his involvement in the killing as "a massive mistake on my part".

Pikula-Carroll also recited letters to Ms Barr and Justice John Burns, saying he would never have participated in the second home invasion if he thought someone would die.

"Whatever sentence is imposed on me, I know that my debt to you will never be paid," he told Mr Waugh's family.

Pikula-Carroll's barrister, John Purnell SC, later told the court that Forster-Jones was "far more culpable" than his client.

He noted that Forster-Jones had been the one who fired the fatal shot, knowing that someone behind the door would "probably" be killed.

Mr Purnell also said Pikula-Carroll had clearly accepted responsibility for his actions.

But Mr Williamson took issue with this, claiming Pikula-Carroll was lying about some matters in order to minimise his culpability.

He also said it was Pikula-Carroll who had set everything in motion by arranging the first home invasion as a form of retribution.

"Without [Pikula-Carroll] taking offence at the failed drug transaction, none of what followed would have occurred," he said.

Mr Williamson said Pikula-Carroll, who also had a far worse disciplinary record than Forster-Jones while in custody, should arguably be jailed for even longer than the shooter as a result.

Justice Burns indicated that he would hand down Pikula-Carroll's sentence on December 1.

Forster-Jones has already been handed a 30-year jail term.

Sikounnabouth is behind bars for 12 years, meanwhile, for crimes including being an accessory to the murder.