Megaupload founder Kim Dotcom has been granted access by a New Zealand high court to all evidence seized during raids in 2012 by the police.
The court said that warrants used in the raid on Dotcom's home were illegal, and ruled that police must provide copies of evidence considered relevant to the US investigation, which include materials forwarded to the Federal Bureau of Investigation (FBI).
The court also ruled that any evidence seized in the raid, including computers, hard drives, files, among others must be returned to Dotocom.
Justice Helen Winkelmann said in a statement the police must review digital data storage devices and return any to the plaintiffs that contain no related material.
Dotcom is seeking damages from the New Zealand government for a raid conducted on his home in January 2012.
He contended that his site was merely a storage facility for online files and argued that he should not be held accountable if stored content was obtained illegally.
The controversial website owner's lawyers, meanwhile, argued that lack of access to the seized material incapacitated them from defending Dotcom and his colleagues against extradition.
The US had lodged a criminal case against Megaupload, accusing it of facilitating online piracy, participating in racketeering and money laundering.
He faces extradition charges after the US Department of Justice accused him of leading a company that copied and distributed copyrighted material worth over $500m (£322m).