A lonely slave who became infatuated with a dominatrix armed himself with a hammer and went to visit her boyfriend to scare him off and destroy explicit videos of the woman.
That plan fell apart when Stuart Lindsay Heron snapped and instead used the hammer as a murder weapon.
The reason he decided to kill Nicholas Cameron may "remain a mystery for all time", Supreme Court Justice Michael Croucher said, as he jailed Heron for more than two decades.
"He may not know, or even want to find out."
Heron had met Melbourne dominatrix, Heide Bos, about two months earlier on fetish and kink website FetLife.
Bos went by the name "Hedonisticsiren" and Heron by "slavepinto".
They began exchanging messages and then came up with a "hare-brained scheme" after Bos started complaining about how her boyfriend was treating her.
Bos claimed Mr Cameron had filmed explicit videos of her and threatened to distribute them to others, so she asked her slave to confront him, scare him off and destroy the clips.
Heron later told a psychologist he took a hammer to smash the camera and memory cards.
He stalked Mr Cameron in the days before the killing, staking out his Southbank apartment building and stealing a lockbox.
After an argument with Mr Cameron, on July 9, 2021, Bos gave Heron the go-ahead to confront him.
He lay in wait in the shadows of Mr Cameron's car park, pouncing on his target as he took his dog Misty for a walk.
Heron ran at Mr Cameron, armed with a knife and hammer, with the pair struggling with each other.
"Incredibly, this went on for around 10 harrowing minutes, Mr Cameron had no chance," Justice Croucher said on Friday.
He "ferociously and brutally" murdered the man, leaving him bleeding to death between a concrete wall and his car, the judge said.
Neighbours called police after hearing Mr Cameron scream "no" and "stop", with authorities finding him "covered in blood, panting heavily and groaning", he said.
The 39-year-old was declared dead by paramedics at 12.45am.
Heron was arrested while waiting for a lift to leave the building, a blood-soaked knife found on the floor next to him.
He was also carrying the bloody hammer, silver hand-cuffs, a dog's leash and a lighter.
Heron pleaded guilty to Mr Cameron's murder about two months before a trial was due to begin.
He was emotionless and stared straight ahead at Justice Croucher, as he was sentenced to 22 years in prison.
Heron, 50, must serve 15 years before he can apply for parole and has already served two years of his sentence.
Mr Cameron's family and friends hugged each other inside court after hearing his murderer's sentence.
A man yelled at Heron: "That's life for you son, you'll never get out of it, you're a failure."
Bos was jailed for up to six years and three months earlier this year, after admitting manslaughter over her complicity in arranging the attack.