FBI agents sent cloned copies of computers seized from Kim Dotcom and his Megaupload colleagues offshore just days after a judge said a court needed to decide if the agents were allowed to take the material, a court heard.
Dotcom's lawyer Willy Akel said the FBI agents committed an "illegal act" when they sent the 18 cloned computers and other items to the United States by the courier company Fedex.
The latest twists in the saga of file-sharing company Megaupload came after Dotcom and co-accused Finn Batato, Mathias Ortmann and Bram van der Kolk asked the High Court at Auckland to rule the search warrant used by police was too broad.
The men were arrested in January at the request of the US Department of Justice which claimed they were in a conspiracy to criminally violate copyright through Megaupload, which carried 4 per cent of the world's internet traffic at its peak.
Questions by Chief High Court Judge Helen Winkelmann led to the discovery the FBI had already taken copies of the evidence in question. Mr Akel said the paper trail showed the copying and sending of the information happened while defence lawyers were negotiating with the Crown and assurances had been given nothing would be sent.
He said it was possible Crown Law had been kept in the dark and it had been "gazumped" by the FBI ahead of the proper court hearing.
Mr Akel said police were operating under a legal direction to keep "custody and control" of the items seized by search warrant.
"If a copy is made and that copy is allowed to make its way to a third party ... then the person in charge of custody and control has lost control."
He said doing so would be an "illegal act".
The key dates in the debate fell in late March. On March 22, North Shore District Court judge David Harvey - who will hear the extradition case - had given the lawyers in the case formal notice of a hearing to work out whether the FBI would be allowed to clone and remove the seized items. The hearing was meant to be on April 2, by which time two courier drops of cloned information had already been sent.
An affidavit from the police officer in charge of the seized material, Detective Sergeant Nigel McMorran, detailed how two FBI agents worked in the electronic crime lab for two weeks.
He said he had contacted the agents to offer to take clones of the items to the United States Embassy only to find they had already sent the clones to the US.
Mr McMorran, who went on holiday for a month that same day, said he "did not make a report" of the conversation.
A judgment is expected this month.