Bronwyn Buttery and her son Christopher Malyschko were also charged in relation to the murder of Mr Niceforo.

Buttery was in a relationship with Mr Niceforo who the judge found was a "very frightening individual" who had physically abused her.

Buttery paid for the murder, was found guilty of manslaughter, and was given an eight-year jail term with a minimum of four years, while Malyschko was sentenced to life imprisonment with a non-parole period of 18 years.

Malyschko and Darren Halfpenny - who earlier pleaded guilty - attacked Mr Niceforo in his flat where Malyschko bludgeoned him to death with a spanner while Halfpenny held him in a headlock.

The judge found Grieve had decided to pull out of the murder plans at the last minute but did not actively try to prevent the death and sentenced him to life imprisonment.

"I take no pleasure in this outcome," Justice Dean Mildren said in 2013 of the harsher sentence meted out to Grieve, who was not present during the murder.

"It is the fault of mandatory minimum sentencing provisions which inevitably bring about injustice."

Grieve was 19 when he was charged and his story made international headlines, culminating in a documentary series and several books.

His release on Friday has sparked renewed calls for a review of the NT's mandatory sentencing laws.

Chief Minister Natasha Fyles said the government is not planning on changing the laws.

"It's not a loophole, it's the law as it stands in the Northern Territory," Ms Fyles told reporters on Friday.

"There are some crimes where the community expectation is that there is a minimum mandatory period of incarceration, and I don't have intentions of changing that."

Grieve's mother Glenice Grieve wrote to the NT Law Reform Commission in 2020 pleading for her son's release.

"Everyone can see mandatory sentencing is wrong," she said.

"Mandatory sentencing means so many people with my skin colour are in prison.

"His life sentence was a big blow to all of us, such a huge punch, that I don't think we ever recovered."