Television New Zealand has also received jailhouse correspondence from white supremacist Philip Arps which holds strong racist views and praises the alleged Christchurch gunman, 1 NEWS can reveal.
The letter, which made it past corrections’ vetting process, is part of a formal Broadcasting Standards complaint and contains anti-Muslim and anti-Semitic hate.
It is the second letter Arps has sent to a major media outlet. A letter sent to MediaWorks reportedly threatened violence against politicians, including the Prime Minister, while the complaint to TVNZ attacked Jews and Muslims.
The development increases scrutiny on a prison system already under significant pressure.
Corrections Minister Kelvin Davis has already promised a new specialist mail management team.
Top lawyer Nigel Hampton QC said ownership for the situation is with corrections.
“The responsibility in a prison is held by the prison manager, it's his or her discretion as to what comes in or out and those prison managers have not been doing, I think, what they should have been doing,” Mr Hampton told 1 NEWS.
ACT leader David Seymour said the situation means corrections has “actually been party to a crime”.
“It is a crime to incite violence, by helping send these letters corrections have actually been party to a crime,” Mr Seymour told 1 NEWS.
Arps’ jailhouse writing delayed proceedings at the Christchurch District Court today, where an appeal was being heard against his 21-month prison sentence for distributing footage of the March 15 mosque attacks.
The judge indicated the letters may constitute "fresh evidence" and asked police to get a copy.
The Sensible Sentencing Trust says while these letters may be high-profile, they're just one example of shocking mistakes they've seen in the past.
"We've had victims being written to from offenders before, we've known of a couple of sexual abuse cases where people have written to the victims and made sexual advances,” Sensible Sentencing Trust spokesperson Jess McVicar said.
Legal experts say the right laws are already in place, prisons just need to follow them.
“Handwritten letters are difficult from time to time and they get boring, but you've got to be trained to overcome that difficulty and overcome that boredom, it's as simple as that really,” Mr Hampton said.
By Simon Plumb and Thomas Mead