Lee McMurdo, 32, was found dead by his 12-year-old daughter Lateasha in the backyard of his Helensville home a year ago.
Police still have few clues about the circumstances surrounding his violent death.
Detective Inspector Greg Cramer, who is leading the investigation, said it was now believed Mr McMurdo had turned to using and dealing drugs.
"It seems he was seduced by them as a means of escaping a difficult financial situation following the collapse of his business," he said.
"I believe that Mr. McMurdo was dealing in the new illicit substance MDVP which is marketed and known as 'bath salts.' MDVP is a stimulant and relatively new to New Zealand, but is widely known in some Scandinavian Countries and parts of the United States."
MDVP has been linked to a number of violent or bizarre incidents around the world, along with a number of overdose deaths.
Mr Cramer said the investigation into Mr McMurdo's death had led to the seizure of illegal drugs, the recovery of stolen property including boats, cars and earth moving machinery and multiple arrests for lower level criminal offending.
"But of course our focus remains on apprehending the person or persons responsible for Lee's death."
A white Mitsubishi Mirage with a black bonnet stolen from west Auckland in the early hours of July 27 last year is believed to be linked to the murder.
It was driven north late on July 31 and is believed to have hit a cow in the Wellsford area, sustaining frontal damage, Mr Cramer said.
He appealed for anyone who had seen the car or had information about Mr McMurdo's death to come forward to police.
"I am conscious that the passage of time affects relationships, friendships and allegiances among individuals and there are those in the community who know about this murder. Someone has the precise information that we need."
Bruce McMurdo, Mr McMurdo's father, said the death had devastated his family.
"A year has passed and it doesn't get any easier, particularly as none of us understand why he died.
"Lee was a much loved son, brother and dad.
"His daughter Lateasha is really struggling to come to terms with losing the father she idolised.
"Lee's two younger children, Bowen and Jazmin, don't understand why their dad is not with them."
