So how did this happen?
Every prisoner has legislatively required minimum entitlements under the Corrections Act 2004.
One of these minimum entitlements is to send and receive mail. In accordance with section 108 of the Act, a prison director can only withhold a prisoner's mail in a very limited range of circumstances. Some of the man's letters have been withheld. But not this one.
It shows how when it comes to rights and privileges - and the control of those rights and privileges by the state - that every case is specific to a person and the crime.
Tell a petty thief he can't write letters in jail then every civil rights warrior would be up in arms. We all would be because it's inhumane and it doesn't sit well in our gut. But with this guy it seems a no-brainer.
It's like the suspension of voting rights for prisoners. Everyone feels in their heart it's the right thing to do - but in the cold light of law, applied equally to every citizen, the courts have ruled it's against the Bill of Rights.
Corrections Minister Kelvin Davis yesterday said the letter should never have been sent but admitted to the difficulty of the situation when he said that New Zealand has never had to manage a prisoner like this before.
Ban his correspondence and he gains attention, allow his correspondence and he gains attention. Either way we're giving oxygen to the fire he is trying to ignite. This will be talkback today: what would you do if you were managing this man?
There is no easy answer to this. It shows you how long and painful the process of bringing this man to justice will be. Just like excising a cancer we have to grit our teeth and commit to the process.
There will always be some regret that a form of summary justice was not carried out on the 15th of March. If you know what I mean.
And by the way. Today marks five months since the atrocity and obviously the wounds have not healed.
* Andrew Dickens is hosting Newstalk ZB's Early Edition this week.