New Zealand prides itself on being a civilised country when it comes to law enforcement. As part of this, people questioned by police enjoy some basic protections: the right to silence, the right to counsel, the right to know why they are being questioned. We have these safeguards to prevent injustice: to reduce the risk of false confessions to police, and to limit the ability of police to stitch up innocent people.
The police have been told that they can ignore all that, if they're willing to spend enough money on it and call it an "undercover operation".
There have recently been two cases which have used the "Mr Big" technique, where suspects are "recruited" into a criminal enterprise (actually a network of undercover police officers pretending to be criminals), and then eventually subjected to an interrogation in order to be able to become a full member. The interrogation is coercive, it implicitly involves detention (suspects are taken to a distant part of the country by their "criminal" associates and implicitly threatened with punishment if they leave), and of course it is conducted without the benefit of counsel or any procedural safeguards. It places strong incentives on suspects to tell the interrogators what they want to hear, meaning that it encourages false confessions. If the police did this openly, there would be no question that the evidence would be inadmissible (and the officers responsible would be disciplined or sacked). But a majority of the Supreme Court have found that it is legal. As one of the dissenting justices noted, the police should not be able to ignore our human rights by taking off their uniforms and pretending not to be police. These are official police actions, paid for with public money. The protections of the Bill of Rights Act and of our legal tradition should therefore apply. To allow otherwise is to allow the state to break its own rules by a subterfuge. And if they are allowed to do that, why should we obey them?
[See also: Andrew Geddis on the Supreme Court decision]