Ben Hoffmann, a Darwin local who allegedly shot and killed four people in a terrifying citywide rampage on Tuesday night, has been charged with four counts of murder.

Northern Territory Police charged the 45-year-old just before 4pm local time, with four counts of murder, two counts of recklessly endanger serious harm and one count of criminal damage.

Police said further charges were expected to be laid at a later date, as Hoffmann was remanded in custody to appear via video link in Darwin Local Court tomorrow.

The 45-year-old had spent the past two days recovering in Royal Darwin Hospital under police guard after he was left with injuries from the alleged shooting, news.com.au reported.

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Footage showed him looking gaunt as he was taken from hospital to Darwin watch house, as police revealed the possible motive behind the attack.

Shooting suspect Ben Hoffmann is taken from Royal Darwin Hospital to jail, before he appears via video link in Darwin Local Court tomorrow. Photo / 7 News
Shooting suspect Ben Hoffmann is taken from Royal Darwin Hospital to jail, before he appears via video link in Darwin Local Court tomorrow. Photo / 7 News

Earlier, cops revealed a row over a woman may have triggered the deadly rampage in Darwin, also admitting they pulled over Hoffmann for speeding just hours before the shooting.

Hoffmann was on parole after being released from prison when he allegedly used a pump-action 12-gauge shotgun to kill four men and seriously injure a woman on Tuesday evening.

Witnesses and NT Police say the gunman was looking for a man named "Alex" when the shooting began. Police later established "Alex" was in fact interstate at the time.

When asked what the relationship between the accused and Alex was, NT Police commissioner Reece Kershaw told reporters: "There may or may not have been an issue relating to a female involved in this."

Police have charged the suspected gunman with four counts of murder. Photo / Facebook
Police have charged the suspected gunman with four counts of murder. Photo / Facebook

Mr Kershaw added that drugs may have been another motive behind the attack. "There is a bit of both there," he said when asked whether the rampage was sparked by drugs or relationship issues.

He said police had pulled the suspect over about 10.52am the day of the shooting at Arnhem Highway, Humpty Doo, for doing 94km/h in an 80km/h zone.

"He was not displaying any adverse behaviour," he said. "There nothing out of the ordinary (when he) was observed by police officers."

Mr Kershaw said he was "very satisfied with our approach" in letting the alleged gunman go.

He said it was a "possibility" the accused was seen with a firearm at the time, but that was still under investigation.

"You have got to treat everyone fairly, and police officers have reasonable suspicions," he said. "They didn't have any at that point in time."

The alleged gunman was given an infringement notice for speeding.

Later that day, as he was arrested, the suspect showed signs of being under the influence of ice, and cops found ammunition, a shotgun and a hunting knife in his possession, police said.

The ammunition and the knife the gunman allegedly used in the attack were bought legally by a "well-known associate of the individual" that morning, police said.

"It was a third party who purchased it," Mr Kershaw said. "(They were) purchased together locally in Darwin on the morning of the offending."

He said police had spoken to the other person who was "assisting with police with their inquiries".

Michael Sisois, 57, has been named as one of the victims in Tuesday's mass shooting across Darwin. Photo / Supplied
Michael Sisois, 57, has been named as one of the victims in Tuesday's mass shooting across Darwin. Photo / Supplied

It comes as a 52-year-old man was killed in the shooting has been identified as Rob Courtney, a New Zealand citizen who is understood to be a security guard at Darwin's casino.

A former work colleague of Hoffmann, Michael Sisois, 57, has also been confirmed as one of the victims. He was shot dead in the carpark of the Buff Club on the Stuart Hwy on Tuesday night.

"Based on what we do know currently, it is highly likely that two victims were known to him and the other two were not," Mr Kershaw told reporters.

He said that the Buff Club and Jolly St victims were most likely the ones known to the alleged shooter.

Police believe the accused did not know the 22-year-old female victim.

The violent event has raised questions about why Hoffman was released in January after serving a non-parole period of four years of his six-year sentence, given his extensive criminal history.

His latest alleged act of violence, while wearing an electronic monitoring device, took place over an hour in areas around Darwin.

NT Chief Minister Michael Gunner has asked for a report from the Parole Board on Hoffmann and another review of all people currently on parole and on electronic monitoring.

NT Commissioner for Corrections Scott McNairn said his department had recommended Hoffmann get parole.

"We take reasoned decisions in terms of how we balance risk and those individuals are thoroughly risk assessed before we make any decision," he said.

Darwin taxi driver Hassan Baydoun was killed in the horrific attack. Photo / Facebook
Darwin taxi driver Hassan Baydoun was killed in the horrific attack. Photo / Facebook

Hoffman had previously breached parole by breaking curfew, for which he was given a 14-day custodial sentence in late April.

When Hoffmann was jailed in 2015, his victim Hussain Garling — who was bashed with a baseball bat in front of his infant son — told the court he "needs to be put away for a very long time, because he will do worse to someone next time". Of the 103 people on parole in the NT, 46 are also being electronically monitored.

The parole report and the review is expected to be completed by the end of next week.

The deadly violence started at 5.39pm on Tuesday at the Palm Motel where Hoffmann allegedly shot and killed taxi driver Hassan Baydoun, 33, who was on a meal break.

Mr Baydoun's cousin Abdallah Salman said his relative did not know the shooter and was accidentally caught up in the shootings as the alleged gunman went from room to room firing his gun and shouting for Alex.

A 22-year-old woman at the Palm Hotel was shot in the legs and remains in hospital in a stable condition.

Over the next hour, the shooter went on to kill 52-year-old casino security guard Rob Courtney at a home in Jolly St, Woolner, a 75-year-old in Gardens Hill Crescent and Michael Sisois, 57, in the car park of the Buff Club in Stuart Park.

Mr Sisois' brother Vincent has lashed out at authorities.

Mr Sisois told Sky News and the NT News alleged shooter Ben Hoffmann was known to be dangerous and should have been behind bars.

"They didn't f**kin' do their job properly ... they knew he was a criminal ... and they let him out. Why?" he asked.

"It's not fair. They're looking after the criminals, not the bloody innocent people."

Hoffmann was tasered and arrested and taken to hospital.

The pump action 12-gauge shotgun used in the shootings might have been stolen, police said.