The man who shot dead his two children in Dunedin before killing himself is understood to have taken the murder weapon from his former flatmate's gunsafe.
The Otago Daily Times understands Edward Hamilton Livingstone got into the safe after accessing a key.
The allegation was yesterday put to Dunedin Clutha Waitaki area commander Inspector Greg Sparrow, who responded with a statement.
It said: "Police identified early on in their inquiries how Livingstone accessed the gun and these details form part of our inquiries and investigation.
"The aspects you have raised form a significant part of our investigations, as do those that specifically relate to Edward Livingstone and his circumstances."
Mr Livingstone's former flatmate could not be reached for comment yesterday.
Police have already confirmed that Livingstone did not have a firearms licence.
Livingstone was the subject of a protection order issued on behalf of his estranged wife Katharine Webb. He made two court appearances related to breaches of the order last year.
Last Wednesday night he arrived at the house Ms Webb lived in with the couple's two children, Bradley and Ellen, armed with a shotgun. He shot the children, then himself.
The director of the University of Otago's national centre for peace and conflict studies, Kevin Clements, said that for a protection order to work it was important the subject had no access to firearms.
He expected police to check any relevant addresses to ascertain the availability of firearms there.
Had Livingstone been able to source the murder weapon from someone he had been living with, there was a "major deficiency in the process", Mr Clements said.
New Zealand had about 230,000 licensed firearm owners and an estimated 1.2 million firearms. An estimated 25,000 firearms were in criminal hands.