The Crown has gone to the Court of Appeal in a bid to overturn the staying of a drug and firearms case involving members of a Nelson gang.
In October 2012, Justice Simon France ruled that the case could not proceed to trial because police had faked the arrest and prosecution of an undercover officer.
Justice France strongly criticised police for arresting the undercover office on fake charges, designed to boost his criminal credentials with the gang he had infiltrated.
Crown lawyer Cameron Mander told the Court of Appeal in Wellington on Wednesday the case should not have been stayed because it didn't rely only on the undercover officer's evidence.
He said Justice France should not have used the stay process to punish police for their improper actions.
However defence lawyer Robert Lithgow said the police actions were a direct attack on the justice system and the Crown was more interested in protecting the case than in the rule of law.
The hearing continues on Thursday.
