The man accused of carrying out the Christchurch terrorist attack has sent seven letters from prison since he's been in custody.
Yesterday it was revealed that Brenton Tarrant sent a letter to a person in Russia, that ended up being published on the 4Chan internet message board.
Two of the seven letters were sent by the accused to his mother.
Today on TVNZ1's Breakfast, Corrections Minister Kelvin Davis said Tarrant - who's being held in Auckland Prison at Paremoremo - sent letters from prison, five of which he didn't know who they were sent to.
When asked by Breakfast host John Campbell whether he knew who the letters were sent to Mr Davis said, "I don't have the names and addresses of those people".
"We're admitting there was a failure in the system and we've got to fix it and make sure it never happens again ... I've said we've got to look at this and sort the system out.
"I've expressed my disappointment at that mistake - that letter should not have been sent - I've said 'Corrections, you need to own this, we need to fix it and we need to make sure it never happens again'."
Under the Corrections Act 2004, sending mail is a legislatively required minimum entitlement for prisoners, however mail can be withheld in a very limited number of circumstances, and Corrections have withheld some of Tarrant's mail where concerns have been identified.
"Some mail had been vetted and this letter should have been withheld as well," Mr Davis said. "The process failed."
Mr Davis also apologised to victims of the terrorist attack, adding "the situation isn't good enough".
"I say I'm sorry - this should never have happened. We know that it has caused immense distress, we know that people are really feeling because of this.
"The safety of the public in New Zealand and the public overseas is our number one priority, that's why we have to sort this out and we have to make sure that it never happens again."
When asked if anyone at Corrections would stand down as a result, Mr Davis said its chief executive Christine Stevenson was doing "wonderful things" in other aspects of the sector.
"This is one area where we have failed. We need to look at it and, like I say, we need to make sure that this doesn't happen again."