Probably everywhere necessary. The snuff video has been adjudged obscene, the way the NZ law works it was always obscene, the censor just confirms it. In practice if you access something like this and once you realise what you're seeing you stop watching then the government isn't going to come after you, but if you share it, keep a copy etc etc you have broken the law enough that you're likely in trouble.
Because it's illegal to have a copy or to publish it the ISPs are likely liable for having transient copies in their routers (these laws were written for film), the ISPs chose to do this initially purely as a public service but now I suspect that they are likely legally liable if they don't make a good faith effort to block these sites (remember ISPs can IP block and DNS block, they can't edit an SSL query on the fly, so everything at that IP will be blocked, if you're hosting your web site along with a snuff film archive I don't have a lot of sympathy for you).
A couple of people have already been in court for sharing it, one is an actual nazi, the other alt-right who may also be an accomplice.
Several people have also lost their jobs for sharing it at work or just plain accessing it at work (this is an action by the companies, not the govt).
There's no real reason why anyone needs to watch this snuff video, except maybe the police themselves as evidence.