The national spy agency will be forced to hand over information to the courts about when it was asked to start snooping on Kim Dotcom and whether it knew the Megaupload founder was a New Zealand resident.
In a High Court judgment released on Thursday, Justice Helen Winkelmann has ruled that the Government Communications Security Bureau (GCSB) must disclose when it was first asked by police to intercept the communications of Dotcom and his co-accused Bram Van Der Kolk.
The spy agency earlier admitted its surveillance of Dotcom and Van der Kolk ahead of the police raid on Dotcom's mansion in January was illegal, because they are New Zealand residents.
Justice Winkelmann said the GCSB must confirm whether or not it has an information sharing agreement with Immigration New Zealand and provide any documents it holds about the residency status of Dotcom, van der Kolk and their families.
The GCSB must also hand over the information it collected about Dotcom and Van Der Kolk.
An application for the GCSB to be added as a defendant in the ongoing judicial review of the lawfulness of the police raid has also been granted by Justice Winkelmann.
This opens the door for Dotcom and his co-accused to seek declarations about the legality of the GCSB's actions and seek damages against them.
It's unlikely the addition of the GCSB to the proceedings would further delay the extradition process, the judgment said.
In her ruling, Justice Winkelmann has also asked for a New Zealand police liaison officer based in Washington to provide an affidavit about whether he viewed a live feed of the raid.
In the February issue of the police online magazine, Detective Superintendent Mike Pannett reported having monitored termination activities around the world in connection with the Megaupload operation from the FBI's multi-agency command centre.
It was earlier ruled that the warrants used to carry out the raid were invalid and as such aspects of the search and seizure were illegal.