There are concerns confidential police informants could be exposed as lawyers realise some blacked-out or redacted material in electronic files can be viewed.
The Southland Times has discovered redacted documents released to defendants in a major drugs case could be viewed if the documents were copied and pasted into a Word file.
Operation Canary targeted a multimillion-dollar commercial cannabis growing operation in Southland and Otago over a four-year period which ended in June 2012.
An investigation is underway and Southland police will seek the return of the electronic files in court, which are in the hands of defendants, on Friday.
Southland Times editor Fred Tullet says more confidential information, including the names of informants or undercover officers could come out once people learn to copy and paste.
Mr Tullet told Radio New Zealand's Checkpoint programme on Thursday that police could be facing a huge problem now that lawyers know it is possible to examine files in more detail.
"If you think back to some of the big cases and some of the sensitive cases - and now that lawyers know if they haven't known before that it's quite possible that they can examine these files in much more detail - police have a major problem with protecting their sources, protecting their confidential informants, protecting their undercover officers."
Fred Tullet said incorrectly blacking-out electronic information is a common mistake, which the Accident Compensation Corporation and the Ministry of Education have had difficulty with.
Mr Tullet said he has spoken to one of the seven accused and seen the prosecution's electronic files that were released to the defence lawyer during the normal discovery process. Blacked-out sections about police sources and information-gathering could be easily accessed.
Isolated case, say police
Southland area commander Inspector Lane Todd said it would appear that the correct process was not followed in relation to how the censored documents were provided to the defence.
Mr Todd said in disclosures of this kind, a paper copy should be provided instead of an electronic version. He would not reveal details of what confidential information has been accessed by defendants, as the matter is before the court.
Mr Todd said police believe this is an isolated case and don't think the privacy or safety of any individual has been compromised.
The convenor of the Law Society's Criminal Law sub-committee says this has an impact on informants and the defence.
Jonathan Krebs said the defence faces a conundrum as to what it does with information which should not have been disclosed.
Mr Krebs said this type of situation puts a dent in confidence in the system, and in future people may think twice about providing information to police.