Investigations are under way into shootings across Darwin's CBD last night.

Here's what we know so far about the incident that left four dead and one injured.

What's the timeline?

The details of the attack have become clearer today.

Police Commissioner Reece Kershaw said the alleged gunman was at Humpty Doo at 4:00pm yesterday.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 7 seconds 1 m 7 s NT Police provide a timeline of the Darwin shooting.

He then attended an address in the Darwin CBD between 5:39pm and 5:52pm.

Commissioner Kershaw said the first emergency call from the public came in from Finniss Street, near the CBD at 5:45pm.

The ABC understands Ben Hoffmann is the alleged shooter. ( Supplied: Facebook )

It's then believed the alleged gunman, a 45-year-old man named Benjamin Glenn Hoffmann, used several vehicles to visit seven other locations across the city.

The four men killed are believed to have been attacked at four different places.

Mr Hoffmann then called the Police Duty Superintendent. It's not clear how he got his number.

Police and the tactical response group apprehended him on the outskirts of the Darwin CBD at 6:44pm.

What do we know about the victims?

Blue Taxi Company have issued a statement confirming that Hassan Baydoun, 33, was one of the victims.

Blue Taxi Company driver Hassan Baydoun has been confirmed as one of the victims of the Darwin shooting. ( Source: Facebook )

The company said the taxi driver had been on his meal break when he was killed.

"Last night in a terrible unprecedented mass shooting, never before seen in our home town, Blue Taxis lost one of their long-term, beloved drivers," the company said.

"Our company is heartbroken and his colleagues are in a state of shock.

"This is not what our city stands for.

"Someone shot having a meal break while going about their own business.

"We pray that we never have to witness anything like this ever again.

"We mourn him and honour him. Our thoughts and prayers go out to his family and friends RIP, Hassan."

Darwin's Muslim community prayed for the victims of the mass shooting as they celebrated Eid. ( Supplied: Asim Razi )

Mr Baydoun's colleague have remembered him as a "genuine, really nice guy", who was always happy to oblige people.

"He was one of our reliable drivers that we would give our regular customer bookings to," his colleague Helen said.

"We frequently had passengers requesting him because he'd provide exceptional service."

She said they did not realise something was wrong until Mr Baydoun missed a booking.

"We were trying to frantically find him because it was so unlike him to not cover the booking," she said.

Mr Baydoun had worked at the Blue Taxi company for 10 years, and was studying when he was killed.

"He'd been working to pay for courses and his future," another colleague, Malina, said.

"He worked very hard to get where he is."

A Blue Taxi, the company which Mr Baydoun worked for, roped off outside the Palms Motel. ( ABC News: Matt Garrick )

The three other victims who died were also men. The injured person is a woman, aged 22.

Police said a 75-year-old man died at Gardens Hill Crescent, a 57-year-old man was killed at the Buff Club in Stuart Park, and a 52-year-old man was fatally shot at Jolly St in Woolner.

Commissioner Kershaw said it was unknown if or how the victims were linked to Mr Hoffmann, and police could not yet identify the victims to the public.

Where did the shootings happen?

Police said the shooter moved across seven different locations:

Palms Motel in the Darwin CBD

Palms Motel in the Darwin CBD Finniss Street in the CBD

Finniss Street in the CBD Jolly Street, in Woolner, about four kilometres from the city

Jolly Street, in Woolner, about four kilometres from the city The Buffalo Club, a local pub on the Stuart Highway at Stuart Park, a few kilometres from the CBD

The Buffalo Club, a local pub on the Stuart Highway at Stuart Park, a few kilometres from the CBD Gardens Hill Crescent, a quiet street near Darwin's public gardens, also close to the city centre

Gardens Hill Crescent, a quiet street near Darwin's public gardens, also close to the city centre A Coles Express service station, close to the city

A Coles Express service station, close to the city Peter McAuley Centre, which is home to NT police headquarters, about 14 kilometres from the CBD

Commissioner Kershaw said some believed Mr Hoffmann was trying to hand himself in at the Peter McAuley Centre, although he was armed and kicked at the door.

What did police know about him?

The ABC understands his name is Benjamin Glenn Hoffmann and he is aged 45.

"He is an individual who is well known to police and has a number of interactions, adverse, with the police force," Commissioner Kershaw said last night.

Commissioner Kershaw said the offender was wearing an electronic monitoring bracelet as he allegedly carried out the attacks and that it was on at all times.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 27 seconds 27 s Police say the alleged gunman was under electronic surveillance.

He said the bracelets were not a "tactical tool" for police, but they would now be able to use information from the bracelet in their investigation.

Mr Hoffmann had recently served "more than a year" in prison, Commissioner Kershaw said.

Corrections Commissioner Scott McNairn confirmed Mr Hoffmann had been on parole since January.

Prior to that he had been sentenced to six years in prison, with a non-parole period of four years.

He said he had been released on parole with 23 strict conditions, and had received one minor breach for breaking his curfew, for less than an hour, and was subject to a 14-day custodial sentence as a result.

How was he arrested?

The details of how Mr Hoffmann was arrested are still not clear.

The Police Duty Superintendent was able to alert the rest of the police force after he received a call from Mr Hoffmann.

The Tactical Response Group was also contacted and involved in his eventual arrest.

Commissioner Kershaw said Mr Hoffmann was crash-tackled to the ground and Tasered before he was arrested.

It's believed the gun was still on him as he was arrested.

Mr Hoffmann is currently being held at Royal Darwin Hospital.

What kind of weapons did he use?

Police said Mr Hoffmann allegedly used a 12-guage pump-action shotgun in the attacks.

It's also believed a knife may have been involved during a fight at the Buffalo Club.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 2 minutes 14 seconds 2 m 14 s NT Chief Minister Michael Gunner confirms four people died and one other injured in Darwin attack

Was the firearm legally obtained?

No.

Commissioner Kershaw said the shotgun was a "prohibited firearm" and it may have been stolen as far back as 1997.

What do we know about the vehicles?

Commissioner Kershaw said police believe Mr Hoffmann used three vehicles during the day.

They're looking for information about:

a Toyota Hilux, NT registration CC26QE

a Toyota Hilux, NT registration CC26QE a red Commodore NT registration CC01IR

a red Commodore NT registration CC01IR a silver Proton, NT registration CD49OU

Was it linked to terrorism?

Commissioner Kershaw said he believed the incident was not linked to terrorism, saying the shooter acted alone.

Who is 'Alex'?

Police have confirmed earlier witness statements that Mr Hoffmann was looking for someone called Alex.

Commissioner Kershaw said police had located Alex interstate — where he was at the time of the attacks — and they've spoken to him.

Here's what witnesses said last night:

"[Another witness] was asleep, heard all the banging and opened the door and the guy was there with his gun, and he just said 'where's Alex?' and he said 'I don't know where he is'," one witness said.

"And he [the gunman] said, 'no worries,' and turned around and started shooting the place up again."

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 3 minutes 14 seconds 3 m 14 s Witnesses describe the moment a man shot people in Darwin's CBD

Has the Northern Territory ever experienced a mass shooting event before?

This sort of violent crime rarely occurs in the Territory.

However, Commissioner Kershaw did draw similarities between last night's shooting and the case of Jonathon Andrew Stenberg in 2013.

Stenberg led police on a six-day search through bushland outside Darwin, after shooting and decapitating his neighbour in New South Wales.

He later pleaded guilty to murder and was sentenced to 25 years' jail. He will be eligible for parole in 2031.

What have the reactions from leaders been?



NT Chief Minister Michael Gunner said thoughts and prayers were with the families and friends of victims.

"This is not the Darwin we know," he said.

Speaking from London, Prime Minister Scott Morrison condemned the "terrible act of violence".

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 27 seconds 1 m 27 s Prime Minister Scott Morrison speaks on the Darwin shooting incident

"I want to extend my deep condolences and sympathy to all the people in the Territory, particularly in Darwin," Mr Morrison said.

"This is a very tight community and I know they will be rocked by these events."

In a tweet, Opposition Leader Anthony Albanese said his "deepest sympathy and thoughts are with the NT community."