In a nutshell, as an Australian he could travel & live freely in both Australia & NZ (kind of like USA & Canada?). While here (NZ) he legally got a NZ "A category" firearms license - so he could legally buy rifles, shotguns and semi automatics with maximum 7 round capacity magazine (yep, that includes AR-15s, AK-47s etc). To have a larger capacity mag on the semi-auto's requires an "E category" license and getting that requires more hoop jumping, but not that hard really. He didn't but acquired high capacity magazines one way or another. Illegally, as he didn't hold the correct firearms license. Another thing, when you buy a firearm here, only the seller and the purchaser know thats' what you've bought, firearms themselves are not registered. So no one really knows just who has what at any time. I was surprised to find out that, actually, for all the scorn we give the USA about "gun rights", our gun laws are more open than the USA's. Australia's gun laws mean that he couldn't have bought those types of firearms in Australia.
If your neighbours don't listen to The Ramones, turn it up real loud so they can. “We didn't have a positive song until we wrote 'Now I Wanna Sniff Some Glue!'” ― Dee Dee Ramone "The Democrats want my guns and the Republicans want my porno mags and I ain't giving up either" - Joey Ramone