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An appeal by Dotcom's lawyers, arguing for access to all the FBI investigation files before his extradition hearing, was dismissed by the Supreme Court at Wellington today.
But the Mega millionaire said he will not be defeated.
Following the decision Dotcom posted a message to his 354,000 followers on Twitter.
"Being defeated is often a temporary condition. Giving up is what makes it permanent," he said.
The defiant message came shortly after a sad-faced emoticon, tweeted immediately after the ruling was announced.
Dotcom, Finn Batato, Mathias Ortmann and Bram van der Kolk are defending charges of mass copyright infringement, online piracy, and money laundering.
Today's judgment comes after the Court of Appeal reversed a decision by the District Court to allow Dotcom the documents.
The District Court decision had been upheld by the High Court, however Dotcom's lawyers were granted leave to seek an appeal in the Supreme Court after the Court of Appeal reversed the decision.
"The District Court was wrong to order disclosure of the documents concerned," Justice John McGrath said today.
"The appeal has been dismissed and costs have been reserved."
The District Court had "no power" to order the US to disclose information, the Supreme Court ruled, saying no argument had been put forward to "suggest that exceptional circumstances exist that would warrant a formal request" for further information from the US authorities.
"There is no indication of a lack of candour on the part of the United States, or any other abuse of process, and the appellants have not pointed to any reason why, without the requested information, they will be unable to meaningfully challenge the case against them," the ruling said.
The Supreme Court said Dotcom and his team would have greater knowledge of how Megaupload worked than the FBI.
"Whereas the United States relies on expert analysis and inference to identify the business structure and operations of Megaupload, the appellants have first-hand knowledge of Megaupload's purpose and business model.
"It cannot be said that the appellants will, without more information, be deprived of the opportunity to properly contest the case against them, as presented in the record of the case."
The defence already had access to much of the information gathered as evidence by the US, the court said.
That includes extracts from a large number of emails, data from Megaupload servers, a network analysis of how the websites operated and an analysis of all the financial transactions.
The proposed testimony of investigators who went undercover as users of the Megaupload websites, and a number of experts in copyright ownership, were also included in the evidence, Justice McGrath said.