Darwin mass shooter Benjamin Hoffmann has told the Northern Territory Supreme Court he feels "horrible" for killing four people in a drug-affected rampage, however has refused to accept ultimate responsibility for his actions.

Hassan Baydoun, Michael Sisois, Robert Courtney and Nigel Hellings were killed during the shooting spree through the Northern Territory's capital on June 4, 2019. 

Hoffmann last year pleaded guilty to three counts of murder and one of manslaughter over the deaths, part-way through what was expected to be a nine-week trial.

His sentencing has faced lengthy delays after he repeatedly fired his legal team and made unfounded allegations his lawyers were working against him.

During his trial, Hoffmann made claims of corruption and coercion, giving handwritten letters to the Supreme Court judge presiding over his case.

Prior to sentencing submissions, despite pleas from his legal representative not to do so, Hoffmann took to the stand to give evidence.

Hoffmann told the court he felt remorseful for his actions and had experienced psychotic delusions and heard voices during the incident.

"I'm really upset, I hate what's happened, and if I could take it all back I would," he said.

However, when prosecutor Lloyd Babb SC asked who was "mainly responsible" for killing four people that night, Hoffmann sat in silence for a long period.

"That's a very good question," he eventually said.

"There were a lot of contributing factors."

Hoffmann said factors such as the visions he alleged to have experienced, the man who gave him the gun, and the fact he had not received psychiatric help also contributed to responsibility for the shootings.

Mr Babb argued Hoffmann was not genuinely remorseful and was fabricating a psychotic break to reduce his culpability for the deaths.

"The offender, in the Crown's submission, executed a plan that he'd been verbalising for days and weeks leading up to the offending, namely he was hunting down and trying to extract vengeance [on someone]."

Sentence to be handed down 'at later date'

Speaking outside court, Hoffmann's legal representative said she believed he was genuinely remorseful and suffered from undiagnosed cognitive and mental issues.

She said he realised disregarding legal advice had once again been a mistake.

"Mr Hoffmann just said to me, 'I'm very sorry, I should have listened to you, and what I did was stupid' and he didn't get any argument from me," Dr Patricia Peterson said.

Justice John Burns will hand down his sentence at a later date.