The Northern Territory's first known contract killer may have accidentally died in his prison cell after heavily using drugs, investigators believe.

Key points: Investigators believe Christopher Malyschko's heavy drug use in prison may have contributed to his death

Investigators believe Christopher Malyschko's heavy drug use in prison may have contributed to his death There was no CCTV camera covering the entry to his cell, so foul play has not been ruled out

There was no CCTV camera covering the entry to his cell, so foul play has not been ruled out Corrections Commissioner concedes drug use is rampant in NT prisons

But investigations are being hampered by a lack of CCTV in the low security section of Darwin's Holtze prison, where the death took place.

Christopher Malyschko, 31, was found dead inside his cell on August 20.

Two separate sources, both with knowledge of the investigation, have told the ABC that police believe a drug-related death was most likely.

Both sources confirmed Malsychko was known to be using synthetic cannabis, which they said was widely available in prison.

The investigators' theory was that he began to choke and was unable to recover due to his drug intoxication.

But foul play cannot yet bet ruled out, as there was no camera covering the entrance to Malyschko's cell, meaning investigators cannot establish if anyone else entered the cell prior to his death.

Both NT Police and NT Corrections declined to comment.

Drones used to smuggle in drugs: Commissioner

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

In an interview on ABC Radio Darwin last week, Corrections Commissioner Scott McNairn conceded drugs were a problem in most prisons, but said the anti-drug measures taken at Holtze were strong.

"We have really good security screening ... we have drug detention dogs," he said.

Commissioner McNairn said there were many ways drugs were smuggled into the prison, including using new technology.

"Sometimes drugs can be held internally, they can be in the mouth cavity.

"I've seen in various occasions drugs have been put in a tennis ball and thrown across the fence.

"Drones are another new initiative," he said.

"It's an ongoing challenge but I'm confident the security screening, staff training and drug detection systems are really, really appropriate."

'Unjust' mandatory sentencing laws

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

Malyschko was found guilty in 2011 of brutally murdering his mother's former fiancé, and was sentenced to life in prison with an 18-year non-parole period.

He accepted $15,000 for the killing from his mother, Bronwyn Buttery, which he distributed between himself and two friends.

The case gained media attention after one of the friends, Zak Grieve, was given a longer sentence than Malyschko even though the judge accepted Grieve pulled out of the murder at the last minute.

The sentence discrepancy came about due to the Northern Territory's mandatory sentencing laws which the judge described as unjust.

The NT Administrator, the equivalent of a state governor, has since amended Grieve's sentence to 12 years.

Buttery was tried with Malyschko and Grieve on a murder charge, but was found guilty of the lesser charge of manslaughter.

She served four years of her eight year sentence.