Megaupload founder Kim Dotcom received a big setback today in his ongoing legal quest to remain free in New Zealand, rather than in a US prison.

Dotcom and his lawyers have lost a bid to force the United States to show them the evidence they plan to use in making their argument that he should be extradited. The Supreme Court of New Zealand published a 123-page ruling today, detailing their decision that the US isn't required to hand over to Dotcom and his lawyers copies of the documents it refers to in its arguments.

"The US has been given a free ride to cherry pick whatever allegations they want," said Ira Rothken, Dotcom's American lawyer. "Now, there's not an even playing field in the extradition proceeding. It's an unfair situation."

Dotcom won't have access to his own data to prepare a proper defense, explained Rothken. That data was taken away from him during the January 2012 raid, which "took it offshore and did not return it," he said in an interview with Ars. "The US took away Kim Dotcom's evidence. Kim doesn't have access to his own data to help defend himself."

There's no appeal from this ruling, which is from New Zealand's highest court. A district court ordered the US to give Dotcom's lawyers the data they wanted, but that decision was then overturned by an appeals court. Today's Supreme Court ruling upholds the appeals court decision. It was a 4-1 vote, with only the court's chief judge voting in favor of giving Dotcom the evidence.

In deciding that Dotcom shouldn't get the evidence, the New Zealand judges took notice of legal precedents from European law, which found that since extradition proceedings don't actually determine guilt or innocence, a charged person isn't entitled to all the "procedural guarantees" of an actual criminal trial.

The extradition trial still hasn't been scheduled precisely, but it could happen as early as July. Despite today's significant setback, Rothken said he's still confident they will prevail in that hearing.

"There's never been a case that we could find, in the history of western jurisprudence, where a cloud storage provider was ever held criminally responsible for the acts of users and user-generated content," said Rothken. "We don't believe this novel theory works in the US, and we also think the New Zealand judiciary will reject it. We look forward to making our arguments to the New Zealand court."

The "cherry-picked" evidence that Rothken was referring to was put on public display in December, when the Department of Justice submitted a 191-page "summary of evidence" laying out their view of the case, including internal Megaupload e-mails and financial data.

In addition to copyright charges, US authorities want to put Dotcom, whose given name is Kim Schmidt, on trial over allegations of money laundering, racketeering, and wire fraud.