The mother of the man accused of the Christchurch mosque attacks says it's unfair Corrections is being criticised for allowing her son to send letters.
Sharon Tarrant told the New Zealand Herald she's worried her only contact with her son might be stopped.
It comes after the Corrections Department confirmed Brenton Tarrant sent two letters from prison that should have been blocked.
Chief executive Christine Stevenson admitted that was an oversight, and said she was putting more checks in place for letters written by prisoners with extremist views.
"I have now no confidence in how we are handling this sort of mail," she told Morning Report.
"From this morning, mail sent by those prisoners who identified as having extremist ideologies or who have registered victims will be centralised and a highly professional and skilled team will look at those letters before they are released or withheld."
She said she was also taking personal responsibility for mail to and from the accused gunman.
But Ms Tarrant told the Herald it breaks her heart to see New Zealand's prison system being hammered when they've never had to deal with anything like this before.
"I want to thank the police who have kept him alive ... Now they are being criticised it's really unfair."
She said writing to her son was "sacred", and other people are making it hard to maintain contact with him - such as the extremist users of the website 4chan, where one of the letters was posted.
Ms Tarrant said Corrections had been "brilliant, kind and compassionate" to her family.