The first victim was identified on Wednesday as 33-year-old taxi driver and Charles Darwin University IT graduate Hassan Baydoun.
Following the attacks, Chief Minister Michael Gunner launched an immediate review into the Territory's electronic monitoring and parole systems, as well as into the Parole Review Board, who granted Mr Hoffmann freedom this year.
"The active shooter threat has dissipated", Northern Territory Police Superintendent Gavin Kennedy told the AFP news agency after the arrest, adding that officers were investigating at least five crime scenes throughout the city.
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According to the Police Commissioner, the alleged gunman was "well-known to police" as he was on parole following his release from prison in January.
Mr Kershaw said he was "very satisfied with our approach" in letting the alleged gunman go.
"We didn't believe this is terrorism related", said Kershaw.
He is now being held at Royal Darwin Hospital for exams.
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.
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"He is an individual who is well known to police and has a number of interactions, adverse, with the police force", he said.
Another witness, John Rose, told The Australian newspaper that he saw the gunman walk into the motel with a sawn-off shotgun.
Local Matthew James helped patch up a woman who had been shot in the leg near the Palms.
Prime Minister Scott Morrison condemned the attack as "a awful act of violence".
"The Northern Territory government will do everything in its power to determine what led to these tragic events and how this violence occurred", Gunner told reporters.
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Police initially said two people died and two others were injured, but later confirmed four deaths.