The Government is set to make changes to the law around mail to and from prison inmates, to give greater clarity for Corrections.
Last week, it was revealed the man charged over the March 15 Christchurch terrorist attacks sent letters from Auckland Prison at Paremoremo.
One of those letters was posted to a man in Russia and later appeared on the internet message board 4chan.
The Government will spend two weeks working out the details before it goes back to Cabinet again for sign off.
Speaking to media today Prime Minister Jacinda Ardern said it's "not about one letter reaching one person", instead it was about the broadcast of hateful messages.
"There should have been a layer of vigilance for this individual.
"No excuses, a mistake has been made."
Ms Ardern said it was important changes to the 15-year-old law - the Corrections Act 2004 - was needed to deal with issues around mail from high risk individuals, such as the use of coded language.
Referring to whether law changes threatened compromising freedom of speech, Ms Ardern said a "common sense test" could be an option.
She expects work on the new legislation will happen in the coming weeks, but would not commit to a completion date.
"In the next two weeks we expect policy information before Ministers ... this is not about politics, this is about victims," Ms Ardern said.
The Prime Minister went on to say victims and families of the March 15 terrorist attack not only deserved an apology over the letters from the accused, Brenton Tarrant, but should see changes made to ensure such an incident wouldn't happen again.
Ms Ardern's comments came after Cabinet today discussed the policies around prison mail.
Corrections Minister Kelvin Davis read the letter after it was uploaded to 4chan and called its release "unacceptable".
The accused man sent a total of seven letters from behind bars and two others were withheld by Corrections and were not posted.
"The letter should not have gotten out - I've expressed that disappointment directly to [Corrections]," Mr Davis said last week.
Today, he told 1 NEWS the Government was looking at the laws to see if they are fit for purpose.
He said Corrections processes were also being analysed to see if they are "up to scratch".
"It would appear that they weren't," he said.
Corrections chief executive Christine Stevenson now has the final say on letters received and sent by the Christchurch accused.
On Friday, it was reported another inmate, white supremacist Philip Arps, sent objectionable letters to major news outlets, including TVNZ.