The report in question is a summary of the investigation into a Green Party complaint that the Government Communications Security Bureau (GCSB) broke the law when it intercepted Dotcom's emails and phone calls.
The New Zealand agency had already admitted its spying was illegal because Dotcom was a resident. Police concluded that its staff did break the law, but there was no criminal intent, so charges weren't laid.
The report, obtained by Fairfax Media, makes a passing reference to "data supplied to the GCSB".
Greens co-leader Dr Russel Norman said it's clear that the GCSB didn't gather all the data on Dotcom itself when it was spying on him in December 2011 ahead of a police raid on his Auckland mansion.
The FBI wanted Dotcom arrested on allegations of internet piracy, and is trying to extradite him.
"Someone supplied data to the GCSB, the question is who," Norman said on Wednesday.
"The only thing that makes sense is that the NSA had access to Kim Dotcom's mobile phone calls in New Zealand — who else could have supplied it?"
Norman says that raises the question of why the NSA had access to New Zealand's phone systems.
Whistleblower Edward Snowden has released explosive evidence of the NSA's spying on other countries, including US allies.
New Zealand's GCSB is a member of the Five Eyes international surveillance network. The others are the US, Canada, Britain, and Australia.