NZ's gun laws are pretty lax. Not much is required to get a gun, other than being 16 and a little paperwork. There's a ban on semi-auto weapons but that's the same everywhere except the USA (which is trying hard to raise public support for a ban).
Full of holes, you're right. Then again, there's so much of the 'story' that came out within the first hour or two - right away. It was like the media of the world already had a statement prepared, with explanations for almost everything, very convenient and tidy. I'd actually expect more holes in a chaotic investigation just minutes old. They pretty much had it neatly wrapped up from the get-go.
That said, there are many things which don't add up, and a lot of red flags.
I'm almost certain it was a false flag, probably a joint project between Mossad, CIA, and NZ elite agency members. They're already talking about tightening up the gun laws, and other Patriot Act type bullshit.