Police appear to have had doubts about the legality of using secret video surveillance even before the Supreme Court's decision in September which deemed the practice illegal.
In papers obtained under the Official Information Act, they acknowledge earlier doubt about the clarity of the law.
In one paper, police comment on a series of options designed to get around the court's decision.
One option says a proposed bill would validate past video camera surveillance as part of a search for physical evidence if that search would have been lawful but for the Supreme Court case.
But police say the option would not provide certainty because it is based on the questionable assumption that the law was clear prior to the Supreme Court decision.