A man alleged to have killed four people and injured another in the Australian city of Darwin used an illegal pump-action shotgun, police say.
The 45-year-old suspect, known to police, was arrested about an hour after the first shots were fired on Tuesday.
Police said he carried out attacks at several locations and may have been searching for a "specific individual".
It was not terror-related, they added.
Authorities have not identified the victims nor the suspect.
However Australian media have identified the gunman as Darwin man Benjamin Hoffman.
One of the victims has also been named as Hassan Baydoun, a 33-year-old taxi driver from Lebanon.
A relative told the Sydney Morning Herald: "It's a big loss... he was one of the best people i knew in my life."
Mass shootings - defined in Australia as incidents with four or more deaths - have been a rare occurrence since the country overhauled its gun laws in 1996, in the wake of a shooting in Tasmania that left 35 people dead.
Those reforms included restrictions on gun ownership and the banning of semi-automatic and automatic firearms.
The weapon used on Tuesday was a prohibited 12-gauge pump-action shotgun. Northern Territory Police Commissioner Reece Kershaw said it "may have been stolen as far back as 1997".
Such a weapon should have been surrendered or destroyed under the government crackdown on firearms at the time, experts have said.
How did the shootings unfold?
The alleged gunman, who had been on parole since January, was wearing an electronic tag at the time. Police said he had served four years of a six-year sentence.
Police said he travelled to several places across the city, including the Palms Hotel in the suburb of Woolner. There he allegedly opened fire in a number of rooms before fleeing.
One man was killed at the hotel, and another person was wounded, police said.
Another person was killed at Buff Club, another at Gardens Hill Crescent and another at Jolly Street. Police said the suspect also went to the Peter McAulay Centre - a police operations base.
Witnesses said the suspect appeared to have been searching for a specific person called "Alex".
"We know he was looking for one individual," Commissioner Kershaw told reporters on Wednesday.
The suspect remains in police custody at the Royal Darwin Hospital and is expected to be charged with murder, he added.
What has been the response?
Northern Territory Chief Minister Michael Gunner said officials would conduct an urgent review of all prisoners on parole in the wake of the shootings.
"The Northern Territory Government will do everything in its power to determine what led to these tragic events and how this violence occurred," Mr Gunner said.
Gun crime is rare in Australia, but it saw its worst mass shooting incident in more than 20 years last year when seven members of the same family died in a murder-suicide.
More recently, a man was killed and three others wounded in a shooting outside a popular nightclub in Melbourne in April.