The Government Communications Security Bureau will have to reveal secret details of their surveillance of Kim Dotcom, in an unprecedented ruling from a High Court judge.
Justice Helen Winklemann has ordered "discovery" of documents related to the Dotcom operation.
Today's ruling also allows Dotcom to pursue the police and GCSB for damages.
The foreign spy agency must disclose anything they shared with other intelligence agencies in the "Five Eyes" intelligence alliance - made up of the US, Australia, UK and Canada. And they must reveal if they carried out surveillance on Doctom's wife Mona and his co-accused Bram van der Kolk.
Winkelmann has also ordered Detective Superintendent Mike Pannett - a police liaison officer in Washington - swear an affidavit if he watched a 'live feed' of the the raid on Dotcom's Coatesville mansion on January 20 from the FBI's multi-agency command centre.
If he did, he should provide details to identify the source of the feed, the locations and events being filmed and the time he watched it. Police yesterday said there was no live feed. But they have declined to comment further on the ruling.
Details of a briefing between Anne Toohey, of Crown Law, and other key players and a later video conference, at the OFCANZ office, in November last year, will also have to be handed over.
Dotcom's lawyer have been asking for documentation on the briefings "but no response has been received," the judge said.
The officer in charge of the operation, Detective Inspector Grant Wormald, must also reveal where and when stationary cameras were placed close to Dotcom's home. The police must disclose if any third parties were involved in setting them up.
Justice Winklemann also wants disclosure of an "in-depth" FBI presentation on the investigation.
The live feed was revealed in a February edition of the police's in-house magazine Ten One.
Winkelmann noted that an affidavit given by Wormald stated "that there was no live coverage of the operations going on at the Dotcom mansion."
She said this contradicted "earlier" evidence he had given at a hearing.
Wormald is already facing questions over testimony he gave the court, saying no other agency had spied on the Megaupload entrepreneur.
Lawyers for the prosecution have argued that some of the information sought is "too broad" and will damage their relationship with the FBI. Revealed details of GCSB activities would also compromise national security and reveal information sharing protocols and practices with intelligence allies.
"Footage of the events, if it exists, would be relevant to assessing the nature of Police actions on site at the Dotcom mansion," Winkelmann said.
She wants to know when Pannett watched the live feed, from where - and who else was there.
The judge also wants to know if anyone else was caught up in GCSB's illegal spying, noting Dotcom believes he was being surveilled much earlier than the spy agency has admitted to.
A senior lawyer Stuart Grieve QC has been given security clearance to look at the secret spy documents on behalf of Dotcom. He was appointed by the court in October.
The latest ruling is another milestone in Dotcom's bid to challenge extradition to the US on copyright infringement charges.
His lawyers have already proved that GCSB's surveillance of the mogul was illegal, and search warrants for the January raid were invalid.
A spokeswoman for Prime Minister John Key - who is responsible for the GCSB - said: "We don't comment on court judgements."
The office of the Attorney-General would also not comment while the case is before the court.