There is also a longstanding convention that parliamentarians don't criticise judges and vice versa -- though many do, on both sides.
The accusation of institutional racism, probably subconscious but nevertheless active, is often made and yet virtually never explored in any depth by government agencies.
The problem is that, from time to time, studies come out asking very pertinent questions which never seem to elicit a response.
A few years ago, a study found that similar offenders committing similar crimes with similar backgrounds of different ethnicities got different sentences.
It found that brown offenders got harsher sentences for committing the same crimes than white offenders.
In the study, there was even a geographical bias. Somebody sentenced in Canterbury was more likely to be imprisoned than in the North Island, and the pattern of different sentencing outcomes was most obvious in Canterbury.
So who is looking? Well, many are watching but not too many people are paying attention, because there is no one body which oversees the whole justice system.
If the chain of events goes that a Maori offender is more likely to be apprehended than not; more likely to be charged than warned; more likely to be arrested than summonsed; more likely to be sent to court than diverted; more likely to be convicted than dismissed; more likely to be imprisoned than to receive a custodial sentence; more likely to serve a longer term than paroled early; more likely to be re-convicted and so on ... then there needs to be a global view. But there are no bodies that do that.
The Independent Police Conduct Authority is complaints-based and only looks at police.
There is a mechanism for complaining about judges which is rarely used, and the thresholds for complaints being upheld are very high.
There is a complaints process for Corrections and for the Parole Board too, but these are complicated and actions usually require some legal guidance that the usual Maori offender, displaying the usual demographics of under-education and lack of financial resources, doesn't have at their disposal.
Legal Aid is not usually available for these purposes.
Other conditions also work against taking action.
The legal gene pool in New Zealand is very small.
People don't like supporting complaints against people they have worked with or appeared in front of and will again in the future when acting for another client on another matter.
None of the agencies would be keen to self-audit because they are busy enough and may not like what is turned up.
Politicians could initiate an inquiry but may well be deterred by the prospect of finding stuff they would rather not know about.
The judiciary hates making comments against the findings of their members because they weren't in the room and listening to all the evidence.
The media does point to stuff from time to time but no real investigative journalism happens these days and it is easier to pull something off the net than make a few phone calls, because nobody is buying a newspaper anyway.
The United Nations visiting expert panels looking at justice issues could do it, but it takes longer than the allocated time and that might force them to look at other stuff under the carpet in other countries, like the United States shootings by police officers, so highly profiled in recent times.
The Making of a Murderer series quickly ignited public interest, so it is plain that there is a mandate for some authoritative body to take the issue seriously.
But the human condition is such that we don't always want to see what we don't want to see.
