Kim Dotcom is challenging the warrants used to seize his fortune in new court documents which accuse the FBI of doubled-crossing his Megaupload company.
The new court filings say the courts need to examine closely the evidence submitted by the FBI when it sought seizure warrants as part of its investigation into Megaupload.
It pointed to a "pattern of governmental misconduct plaguing proceedings" in New Zealand and said the FBI secured judicial backing to go after Megaupload by misrepresenting help the file-sharing company had given during the investigation into an internet pirate.
"This is huge," Mr Dotcom tweeted, announcing the filing. It was proof of the "US government acting in bad faith" and the Department of Justice "misleading". Mr Dotcom and three colleagues are facing extradition to the US on charges of criminal copyright violation, which they deny.
The claim of dishonesty hinges on testimony given by the FBI of Megaupload knowingly acting as a haven for illegally copied movies. The testimony was given a year ago in hearings which saw warrants issued for Dotcom and his business associates.