FBI agents who copied data from Megaupload founder Kim Dotcom's computers and took it overseas were not acting illegally because information isn't "physical material", the Crown says.

The agents were accused of underhanded behaviour by Dotcom's lawyers in the High Court at Auckland yesterday, after revelations that the information was already in US hands.

Megaupload's lawyer, Willie Akel, told Justice Helen Winkelmann how two FBI analysts flew to New Zealand on March 20 and reviewed seven hard-drives of information. The analysts cloned the computers in Manukau.

When police returned to pick them up to take them to their hotel, the agents had already left to FedEx the copies back to the United States.

"The first [copies] were sent without the New Zealand Police having any say in it whatsoever," Mr Akel said. The commissioner of police had "lost control of the items" once the FBI had them.

"If [they] went offshore without the consent of the attorney-general, it was an illegal act."Mr Akel said that there had been an agreement that none of the evidence against Dotcom, seized after his arrest, would be provided to the FBI without prior agreement.

However, Crown lawyer John Pike, for the attorney-general, said the material stored on the hard drives could be shipped overseas for the FBI to examine because it did not constitute "physical" material.

The relevant legislation applied only to physical possessions rather than information, Mr Pike said. "[Information] may be the most valuable thing we have, but it is not scooped up by the act".

He said that there were "gremlins" all through the exercise, which made the situation difficult to understand. "Nothing of the physical items have gone overseas and that was our undertaking."

Justice Winkelmann said that there was an obligation that material deemed irrelevant to the investigation be returned.

However, Mr Pike said it was too difficult to know what was relevant and what was not. "Police, to put it bluntly, would not have a clue what is relevant and what is not relevant. How could they?"

Dotcom, 38, is on bail awaiting an extradition hearing.

US authorities say he and his three co-accused – Mathias Ortmann, Fin Batato and Bram van der Kolk – used Megaupload and its affiliated sites to knowingly make money from pirated movies and games.