The man who orchestrated the Northern Territory's first known contract killing has died in Darwin's Holtze prison.

Key points: Christopher Malyschko, 31, was found dead in his cell on Tuesday morning, sources say

Christopher Malyschko, 31, was found dead in his cell on Tuesday morning, sources say He was serving a life sentence for murdering his mother's partner, Ray Niceforo, in Katherine in 2011

He was serving a life sentence for murdering his mother's partner, Ray Niceforo, in Katherine in 2011 His accomplice Zak Grieve, who was not present for the killing, received a longer sentence than Malyschko, due to mandatory sentencing laws

Sources have told the ABC that Christopher Malyschko, 31, was found dead in his cell at the prison complex on Tuesday morning.

Northern Territory Police have not yet formally confirmed this, but released a statement saying they were "investigating the circumstances surrounding the death of a 31-year-old man at the Darwin Correctional Centre this morning".

Malyschko stood trial for the murder of his mother's partner, Raffaeli 'Ray' Niceforo, in Katherine, about 350 kilometres south-east of Darwin, in 2011.

He pleaded not guilty, but admitted on the witness stand to bashing Niceforo's head eight times with a wrench.

Malyschko's defence team argued he should be found guilty of the lesser offence of manslaughter, saying he was acting in defence of himself and his mother, Bronwyn Buttery.

Buttery and Malyschko alleged Niceforo had made a series of threats against them, and they feared for their lives and were provoked by the victim into their actions.

While Buttery was successful and was ultimately found guilty of manslaughter, Malyschko received a majority jury verdict of guilty of murder, indicating that at least some jurors thought he should be not guilty of that charge.

He was sentenced to life in prison with a non-parole period of 18 years, and had served eight years when he was found dead.

Ray Niceforo at Katherine Police Station a month before he was murdered. ( Supplied: NT Police )

'It was either his life or mine'

Malyschko moved to Katherine from Mount Gambier in South Australia in February 2011, looking for employment opportunities to save up for his wedding — which was later cancelled.

His mother was already living in the small town with her new partner, Niceforo.

Chris Malyshko gives evidence in court. ( Artist: Elizabeth Howell )

Malyschko and Niceforo instantly disliked each other, often breaking out into arguments about the young man's work ethic and relationship with his mother.

By September 2011, Niceforo's relationship with Buttery had deteriorated and she took out a series of domestic violence orders (DVO) against her former partner.

But after a series of vile text messages sent from Niceforo's phone to Buttery, and threats he made against the lives of her two sons, Malyschko approached his mother and offered to have Niceforo killed.

"He said words to the effect of: 'I know three people that can do it. It will cost $15,000, mum. Don't ask me who it is 'cause you don't know them anyway, and I won't tell you who they are because if you don't know who they are you're not going to be able to connect it'," Buttery later told police. "And I said to him, '$15,000?' and then he said, 'and it will have Ray out of your life forever, mum. He'll never be able to hurt you again.' "And because of what happened with the breaching of the DVO I thought, 'yep, why not?'. "I said to Christopher, 'OK, I'll get the money'. I felt it was either his life or mine."

'You should have just kept quiet'

Malyschko organised the murder with two friends, Zak Grieve and Darren Halfpenny, though Malyschko said in court that Grieve later backed out of the murder plot.

He said he and Halfpenny let themselves into Niceforo's Katherine flat on the night of October 23, 2011, with a key his mother had given them, and that he confronted them in the hallway.

"I honestly cannot tell you how many times I hit him," Malyschko said to the prosecutor during his murder trial.

"I couldn't stop myself from hitting him ... I felt angry.

Blood and discarded clothes on the floor of Ray Niceforo's flat. ( Supplied: NT Police )

"I remembered everything that had happened between Ray and myself — things that my mother said about Ray, about him strangling her, about him being a violent person."

Halfpenny described Malyschko's actions as "caving in some c***ts head".

They two young men then hastily dumped Niceforo's body on the side of a road leading to Katherine Gorge — the region's biggest tourist attraction — where it was found the next day.

Malyschko, Halfpenny and Grieve were arrested three days later.

While in custody, police phone taps revealed that Malyschko was trying to protect his mother from her involvement in the murder plot.

When she called him to tell him she had been arrested and charged with murder, he replied: "You should have just kept quiet."

Halfpenny pleaded guilty to murder, and contradicted Malsychko's evidence that Grieve pulled out of the plot.

The case gained national media attention after Grieve was given a longer sentence than Malyschko, despite the trial judge accepting his story that he was not there at the time of the murder.

A yellow tent covers Ray Niceforo's body in bushland just off the road to Katherine Gorge. ( Supplied: NT Police )

Niceforo 'bullied, intimidated' Buttery, judge says

In sentencing, Justice Dean Mildren said "there was considerable provocation by the deceased which largely brought about his own death".

He also said Malyschko was aware of the extent to which Niceforo "bullied her, intimidated her, and of the way he treated you and of the threats which he made to yourself".

"It must have been very difficult for you to watch the way your mother was treated by the deceased when there was nothing you could do to interfere on her behalf," Justice Mildren said.

"It is very difficult to put into words the pressure that behaviour of this kind places on an individual."

He said Malyshko had expressed remorse for the murder.

Bronwyn Buttery said she feared Ray Niceforo would kill her if she tried to leave him. ( Supplied: NT Police )

"You said on a number of occasions that you were sorry that you were compelled to kill the deceased, and wished it had not been necessary," Justice Mildren said.

"I doubt if you are really genuinely remorseful in the full sense of that word, although I accept that you believe that you were justified in taking the deceased's life, and wished that this could have been avoided."

But he said the crime was serious and warranted serious punishment.

"You were the one who did the planning, bought the rope, the gloves, and the shower caps, decided which weapons were to be used, and plainly you intended to kill the deceased, and harboured this intent for some weeks before the killing took place," Justice Mildren said to Malyshko.

"It was you who involved Halfpenny and Greive. It was you who paid the money to them from the funds provided by your mother."

Under the NT Coroners Act, an inquest must be held for a death in custody.