Protecting the detection of a non-crime

Back in February we learned that police were monitoring and arresting "courtsiders" - people who leveraged the speed difference between the internet and broadcast media to rip off foreign bookies - during the cricket world cup. Which raised a few eyebrows because it doesn't seem to be against New Zealand law. Someone used FYI, the public OIA request site, to ask for further information about this surveillance. The response is Kafkaesque:

The practice known as 'courtsiding' is not a crime under New Zealand Law.

The request for this information [on the surveillance, including training material and which social media accounts were monitored] is declined under Section 6(c) of the Official Information Act 1982 in that supplying the information would be likely to prejudice the maintenance of the law, including the prevention, investigation, and detection of offences.

So its not a crime, but the information has to be withheld to protect the police's ability to investigate it. Right. Sounds more like self-serving secrecy to cover them overstepping the mark to me.