Accused mosque shooter's letter posted to 4chan

Brenton Tarrant, the man charged in relation to the mosque shootings in Christchurch massacre, in the dock at Christchurch District Court for his first appearance on 16 March. - Photo: Supplied / Pool

The Corrections Department has admitted it should not have let the man accused of the Christchurch massacre send a letter from prison that has been posted on the 4chan website.

Brenton Tarrant wrote the six-page letter in July.

In a statement, Corrections said prisoners were able to send and receive mail, but there can be restrictions in limited circumstances.

It said the letter should have been withheld and it's now changed the way it manages the accused gunman's mail.

In a statement, Corrections minister Kelvin Davis said Corrections should not have allowed the letter to be sent.

"We have never had to manage a prisoner like this before - and I have asked questions around whether our laws are now fit for purpose and asked for advice on what changes we may now need to make.

"I know a lot of New Zealanders will be surprised to hear that this offender is allowed to send and receive mail - but there are rights every prisoner has under the law as it stands.

"Corrections do have the right to withhold correspondence in accordance with the Act - and they have used this power to withhold some correspondence the prisoner has attempted to send, and some he was to receive.

"I do not believe that Corrections should have allowed this letter to be sent and have sought assurances from them that there will be an enhanced process from now on. I have made myself clear that this can not happen again."

Meanwhile, it was announced today Tarrant has been excused from his next court appearance.

The 28-year-old Australian national faces 51 charges of murder, 40 of attempted murder and one charge of terrorism.

He was set to appear in the High Court at Christchurch tomorrow morning for a case review hearing.

But his lawyers have advised they don't need him in court and he does not wish to attend.

It's not unusual for defendants - particularly those held in custody - to waive their right to appear in court.