A former head of gun licensing claims the man charged with the Christchurch mosque shootings wasn't interviewed in his home and his references came from online chatroom acquaintances.

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Guns and gun ownership have dominated discussion since 50 people were killed and another 50 injured at two Christchurch mosques last Friday - one of the big questions being, "How did this happen?"

One ex-cop and arms control officer, Joe Green, says he's got a source alleging gun licensing procedures weren't properly followed.

"I would sooner not disclose exactly who that person is, but who I think is a highly reliable informant," Mr Green told 1 NEWS,

The informant's damning information claims the alleged gunman's application wasn't lodged in Dunedin where he lived, but filed in Waikato.

The source also says no relatives were interviewed and that authorities instead talked to two referees the accused allegedly met in a chatroom, and there are now doubts over whether a home visit and security inspection took place.

"Visiting a person's house enables you see what their lifestyle is like. You might see a little bit of the stuff they get up to," Mr Green said.

This afternoon, Police Commissioner Mike Bush said the vetting process behind how the alleged gunman got a license is under major review.

"That's a very important phase of our investigation. We're working through everything we know about the person who is charged with this horrendous offence," he said.

But almost a week after the attack, Mr Bush couldn't answer key questions, including whether the Dunedin-based suspect applied in Waikato.

"We'll be working through every one of those suggestions so that when we answer you we can definitively, having known all the facts," he said.

Mr Bush couldn't say whether the accused used online acquaintances as referees.

"We'll be working through that as a phase of the inquiry. When I have all the answers, definitively, I will share them."

Nor could the Police Commissioner say whether a face-to-face interview was done.

"That's part of what we're working through."

Mr Green said: "You're looking for a needle in a haystack with firearms licensing. You're looking for that one person in a thousand who's going to go bad."