Police say they had no idea convicted criminal Quinn Patterson had acquired a stash of firearms, nor did they have any system to monitor him.
Property inspectors Wendy and Natanya Campbell were killed on Wednesday after entering Patterson's house in Whangarei.
"We had no idea that that was going on at Mt Tiger Road," says Northland District Commander Superintendent Russell Le Prou. "I can't act on what I don't know."
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The family of the deceased have told Newshub they do have questions about how the gunman accessed the firearms, but say for the moment they're focused on honouring their loved ones.
Natanya Campbell's family say it's impossible to comprehend what's taken place at the house on the hill at Mt Tiger Rd.
"She was a great mum," Natanya's cousin Vicky Martin says. "Beautiful partner with her husband Pete. She was sporty, outgoing, very helpful [and] very, very caring.
"She's got four daughters. The youngest is 3 [and] the oldest is 19. They're just obviously broken... really broken."
Newshub has revealed Quinn Patterson never had a firearms licence, but managed to acquire shotguns, pistols and grenades by using fake names and addresses.
The Campbell family want answers - but say for the meantime, their focus is on getting the bodies of their loved ones home.
"It's a tragic time for everybody," says cousin Nore Martin. "But we'll pull together and focus on keeping each other strong and in time then we can start asking about why we are here now."
The shooting has brought back traumatic memories for former police dog handler Bruce Howat who was stabbed in the arm by Patterson 34 years ago.
"I knew [after being stabbed] I was seriously injured because there was blood running out the crotch of my trousers," he told Newshub.
"I went down the death tunnel... I was travelling towards the light but then I remembered I hadn't said goodbye to my daughters so I went back."
He says those who knew about Patterson's stash of illegal weapons needed to speak up.
"The blood of those dead people is on their hands because their silence played a role in this happening."
Patterson's friend Ross Thompson says he never thought his mate was capable of killing, and only ever witnessed Patterson test firing his guns against bullet proof vests.
"He used to go and test his bullet proof vests outside. He'd load up it up and boom, boom, boom."
It appears the attack on Wendy Campbell and her daughter was premeditated and planned. Newshub can reveal Patterson had rigged up a CCTV camera system at his property.
"He had cameras everywhere," Mr Thompson says.
Police have recovered the remains of Quinn Patterson's body, alongside what appears to be a firearm, and a post mortem will be carried out tomorrow.
Newshub.
