Convicted murderer Matej Vanko will not be released until late 2036 after being involved in a massive riot at a Darwin prison in 2020 that led to several buildings being set on fire and tear gas being used on prisoners.

Vanko is currently serving a life sentence after kidnapping his boss and murdering his brother in rural Darwin in 2012.

The former SERCO detention center worker held his former boss Noelene Stevens captive at a property in Howard Springs and killed her brother Donald Stevens, 53, by stabbing him in the back of the neck.

Four years later, in 2016, he pleaded guilty to aggravated assault on a fellow inmate, resulting in his non-parole period being extended until February 2036.

The 47-year-old will now add rioting to his criminal history after pleading guilty in the Northern Territory Supreme Court to two charges including taking part in a riot and damaging property in relation to a disturbance at Darwin Prison in 2020.

During the riot, a group of prisoners escaped from their area and three buildings were set on fire and ransacked.

Judge Meredith Huntingford said on Monday that the riot began on the evening of May 13, 2020, when a prisoner in Sector 6 broke a glass window and escaped from the building, prompting other prisoners to “make preparations to escape from where they were staying”. .

A group of inmates, including Vanko, managed to pass through multiple areas by overcoming fences for more than 4 hours and then forced their way into the sports and recreation facility and training building.

Judge Huntingford said Vanko was seen on CCTV trying to break the glass door of the sports and recreation building with a fire extinguisher.

At one stage the group climbed onto the roof of the training building before an unknown person started a fire, causing serious damage and rendering the facility “inoperable”.

“Prison officers gathered at the entrance to the training building and observed various inmates dangerously throwing office items from the roof, making threats to prison officers and generally creating a disorderly atmosphere,” the judge said.

He said Vanko was not involved in any arson, did not harm anyone or use offensive language towards prison staff.

The judge said the cost of the damage caused by Vanko was “not insignificant” but that it constituted only a “fraction” of the total bill, which reached $27 million.

During sentencing, the judge said the offense was “prolonged”, occurring over a four-hour period, and involved the use of a “makeshift weapon”.

“It is clear that your behavior was violent and had the potential to cause persons in the area, including correctional officers and other unrelated inmates, to fear for their safety,” he said.

Vanko was sentenced to a total of 18 months in prison for both offences, with his non-parole period extended by six months until September 2036.