The chief executive of Corrections won't say if she will resign if more extremist mail gets out of prisons.
Newshub revealed earlier this week a letter from the accused Christchurch gunman Brenton Tarrant - including a call to action - made its way to Russia before being posted on website 4chan.
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Corrections boss Christine Stevenson told The AM Show on Friday it's not good enough.
"We have very high standards of public safety and we've fallen very short of those high standards."
She said she's taken responsibility for the mistake and it won't happen again, but wouldn't go as far as to say she would quit if there is a repeat.
"Let's cross that bridge if it happens... I've guaranteed it won't."
Tarrant's mail was screened by an intelligence analyst and the prison director at Auckland Prison, but Stevenson says their decision to let the letter on 4chan through was a mistake.
She's still working out what steps to take next with the pair.
"I truly haven't thought about the employment consequences or something like that nature - my work over the last day has been to get control of this, to apologise and to be accountable. Any employment considerations will follow."
Meanwhile, the Corrections Association is calling for a law change to give more powers to guards.
"We don't have the ability to read letters - we're only allowed to scan them, and if we see something that's untoward, can forward to a manager for a decision," president Alan Whitley told Newshub.
He said officers miss things when they're scanning the letters, and there needs to be a legislation change allowing them to be read in full.
More letters have made their way out of prison recently, including one from racist Philip Arps, which called for the public execution of Prime Minister Jacinda Ardern.
Tarrant has sent five other letters to unknown recipients that were not published on 4chan.
Corrections has now changed its processes for reviewing mail for prisoners with extremist views - it will now be managed by a centralised specialist team.