An international all-star lineup of the White House's most-loathed shared a stage in New Zealand's largest city for a rally billed by the event's host, Kim Dotcom, as the Moment of Truth.

Bathed in red and white lights and cheered on by a capacity audience of about 1,500 at the Auckland town hall, the internet entrepreneur turned political party founder sat alongside journalist Glenn Greenwald at a table emblazoned, in case there was any doubt, with the words the Moment of Truth.

On the big screen above, Greenwald's source, NSA whistleblower Edward Snowden, was beamed in live from Moscow, while fellow fugitive Julian Assange peered from a screen beside him, also beamed in live from the Ecuadorian embassy in London.

All were given thundering ovations from a crowd who, five days away from New Zealand's general election, were energised by articles published hours earlier by Greenwald and Snowden alleging mass surveillance in New Zealand and duplicity on the part of the prime minister, John Key.

Greenwald, whose arrival in New Zealand on Friday ignited another powder keg in an already explosive election campaign, began by marvelling at the criticisms he has faced from Key, who has labelled him "Dotcom's little henchman" and a loser.

"It is not all that common to arrive in a country, and within 24 hours, literally, find oneself being publicly maligned and attacked by the nation's head of state, using the most adolescent epithets imaginable," said Greenwald to applause, and peals of laughter from Dotcom.

He dismissed Key's claim of political motives as "reckless accusations".

Key has repeatedly rubbished Greenwald's claims of mass surveillance by the New Zealand spy agency, the Government Communications Security Bureau, a member of the NSA-led Five Eyes alliance, saying that while the government had considered a programme for "mass protection", he had rejected the GCSB proposal.

Within hours of Greenwald and Snowden's articles being published on the Intercept website – drawing on NSA documents that detailed a programme called Speargun, which involved a "cable access" tap, apparently into the undersea cable that connects the New Zealand internet to the world – Key had responded by releasing declassified documents which proved, he said, that the claims were "simply wrong" and "based on incomplete information".

Greenwald hit back with an express-pace address at the town hall. "He's not releasing that classified information for any other reason than protecting his reputation and for political gain," he said.

Retracing the evidence in the Intercept report and an accompanying article by Snowden, Greenwald said: "The Key government has radically misled and deceived the New Zealand citizenry. I don't make that accusation lightly … unless I have the evidence to back it up. And in this case I can categorically and with great confidence say that it is."

The biggest roar of the night greeted the arrival on the big screen of Snowden, white earphones dangling from his ears. His contribution, the most compelling of the night, began with a new piece of information: the NSA had a facility somewhere in Auckland, and another further north.

As to Key's denials, Snowden detected a "careful parsing of words". His own experience as an NSA analyst, he said, left him with no doubt that New Zealanders' communications were swept up by the XKeyScore mass surveillance programme.

"Maybe the people of New Zealand think that's appropriate," he said. "Maybe they think that they want to sacrifice a certain measure of their liberty … That's what democracy is about; that's what self-government is about. But that decision doesn't belong to John Key or officials in the GCSB making these decisions behind closed doors."

Next came Assange. The WikiLeaks founder first apologised for the background noise of mysterious tunnelling – building works were under way in the flat below the embassy. He went on to lay out the "wider context" for the spying revelations: New Zealand had been "effectively annexed", he said, a tired voice competing with the incessant hammering of a power tool.

Dotcom, who is wanted in the US for alleged copyright infringements around his now defunct Megaupload site, lavished praise on his guests. "You are heroes and I thank you very much for letting humanity know what is going on," he enthused.

There was no "moment of truth" from Dotcom, however. The Internet party's founder and "visionary" – as a non-citizen resident he is prohibited from standing for parliament – had promised to produce evidence to support his belief that Key had colluded with Hollywood executives to deny him residency in New Zealand in 2010, in preparation for an extradition attempt to the US.

Key has consistently said he knew nothing of Dotcom's existence until the eve of the dramatic FBI-backed raid on his north Auckland mansion in January 2012.

The anticipated "big reveal" had been published in the New Zealand Herald several hours before the town hall extravaganza. It came in the form of a purported email from 2010, in which the Warner Bros chairman informed a Motion Picture Association of America executive: "John Key told me in private that they are granting Dotcom residency despite pushback from officials about his criminal past. His AG [attorney general] will do everything in his power to assist us with our case. VIP treatment and then a one-way ticket to Virginia [where charges would be filed]."

The email which, according to the Herald, was "the evidence Dotcom is planning on producing at the Moment of Truth event", was quickly dismissed as a fake by Warner Bros and the MPAA, while Key said no such conversation took place.

The disputed email was mentioned only fleetingly during the Monday night rally by lawyer Robert Amsterdam, who said it had been referred to the parliamentary privileges committee. However it dominated a heated press conference afterwards. Attempts to prevent discussion of the disputed email on the basis it would be the subject of an inquiry were scoffed at by journalists seeking information on its provenance and authenticity.

Greenwald was largely a bystander as Dotcom responded to questions by chiding the media: "You have failed us in the past. You need to wake up and do your jobs."

Dotcom insisted the email was genuine. "I believe it to be 100% real," he said. "Everything I've produced in the past, everything I've said in the past, has been proved true."

He may need to produce proof promptly if he wants to dent Key's chances of surviving Saturday's election.