New Zealand's Green Party is accusing New Zealand Police of operating a double standard in its investigation of the illegal bugging of Mega Upload founder Kim Dotcom's communications by security agency GCSB.

After Fairfax Media released the executive summary of the investigation today, Green Party co-leader Dr Russel Norman expressed his disappointement with the investigation.

"This report highlights the police's once-over-lightly approach when faced with investigating this serious breach of the Crimes Act, which is in stark contrast to their vigorous investigation of the same breach in the much less serious 'teapot tape' saga," he said.

The teapot saga referred to was an investigation into a journalist who left a tape running while New Zealand Prime minister John Key met with ACT Party leader John Banks during the 2011 election.

The Police investigation into the bugging of Dotcom was in response into the complaint laid by Norman against the Government Communication Security Bureau (GCSB).

The Police report says intent is required for an offence to have been committed in the case. Anyone who honestly but mistakenly believed the interception was conducted in accordance with the law would not be criminally liable.

No enquiry was made by GCSB into the targets' immigration status and it could not be established whether data was gathered "at rest or in transit".

Collection of data in transit is required to meet the Crimes Act definition of interception, the report says.

At the time of raids on Kim Dotcom's mansion north of Auckland he was a New Zealand resident and therefore GCSB was not legally allowed to intercept his communications.

"The report shows that the GCSB didn't fully cooperate with the investigation, and the police exerted little effort to try and fully investigate the complaint. They simply relied on the cooperation of GCSB staff; cooperation that was far from fulsome," Norman said today.

"Nearly one third of the GCSB staff that police wanted to interview were not spoken to. One of those who declined to be interviewed appears to have played a crucial role in the GCSB's actions in this case, yet police didn't pursue this any further despite the seriousness of this matter."

The police chose not to prosecute anyone, despite finding that the GCSB did illegally spy on Kim Dotcom and Bram van der Kolk, Norman emphasised.

In contrast, during the Teapot investigation, police seized personal cellphone logs and messages and raided media outlets to prevent publication of the recordings.

Both cases related to s216(B) of the Crimes Act, which bans the interception of private communications.

"We would like to see the police do their job in a measured, thorough, and apolitical manner, rather than what we've seen in these cases where they've either overreacted or underreacted," Norman said.

Prime Minister John Key is the Minister responsible for the GCSB.

The Independent Police Conduct Authority (IPCA) is currently investigating the police's handling of Norman's initial complaint, including the decision not to prosecute anyone as well as the police's failure to investigate the additional 85 potential breaches by the GCSB.