Benjamin Glenn Hoffmann pleaded guilty mid-trial in November to intentionally killing Hassan Baydoun, 33, Michael Sisois, 57, and Rob Courtney, 52, and the manslaughter of 75-year-old Nigel Hellings, on June 4, 2019.
The 48-year-old is scheduled to return to the Northern Territory Supreme Court on Thursday for sentencing on a total of eight charges, including three counts of recklessly endangering life and one of threatening to kill.
Hoffmann was high on methamphetamine when he shot the four men dead while hunting a man named Alex Deligiannis, who he believed had stolen his ex-girlfriend, Kelly Collins.
He shot Mr Baydoun four times with a double-barrel shotgun at the Palms Motel in central Darwin.
Mr Hellings was gunned down through the front door of his apartment block about 800m away.
Hoffmann's next victim was his mate, Mr Sisois, who he shot in the head in the car park at the nearby Buff Club bar and restaurant.
Mr Courtney was murdered at an industrial yard at Darwin Recycling, about 2.5km away.
He was found with 69 injuries, including 36 stabbing and slicing wounds, multiple blunt force injuries and a gunshot wound.
Mr Deligiannis had previously visited three of the locations regularly.
Hoffmann and Ms Collins met in early 2019 in a drug rehab centre, where the pair made plans to move in together after they left the program.
But two weeks before the shootings, Ms Collins sent Hoffmann a text message saying she was in love with Mr Deligiannis.
In July, Hoffmann told the court his world was turned upside down in the lead-up to the killings when he learned Ms Collins had resumed using methamphetamine.
"Things spiralled out of control with Kelly. Too much was going on for too long," he told Justice John Burns.
Hoffmann said a group of men had been feeding Ms Collins drugs and pimping her out and raping her.
"She had guys stalking her that were stalking me," he said.
He told the court the pair met "naturally" while they were drug-free at the rehab centre after he was released from prison and planned to move in together, but her regression had left them vulnerable.
"That part of my life out of control and the stress and the fear it put of me trying to get her to a safe area. I tried to save her. I feared for my life and my girlfriend," he said.
On the day of the killings Hoffmann believed Ms Collins, an ex-prostitute, was in danger and likely to have been physically harmed.
"I had full visions of Kelly being held against her will as a hostage. The night before I was convinced I'd been poisoned and I believed she had been too," he said.
Hoffmann also said he believed various groups of men were out to get him, including an outlaw motorcycle gang.
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