The first rendezvous in Kowloon

Then Edward Snowden delivered a bombshell ... He said he had got hold of Presidential Policy Directive 20, a top-secret 18-page document issued in October 2012. It said that the agency was tapping fibre optic cables, intercepting telephone landing points and bugging on a global scale. And he could prove all of it. “I almost fainted,” Laura Poitras says. The source made it clear he wanted Glenn Greenwald on board.

Poitras moved ultra-cautiously. It was a fair assumption that the US embassy in Berlin had her under some form of surveillance. It would have to be a personal meeting. In late March, she returned to the US and met Greenwald in the lobby of his hotel, the Marriott in Yonkers. They agreed that they needed to get hold of the national security documents: without them, it would be difficult to rattle the doors on these issues. Poitras had assumed that Snowden would seek to remain anonymous, but he told her: “I hope you will paint a target on my back and tell the world I did this on my own.”

By late spring 2013, the possibility of a meeting was in the air. Snowden intended to leak one actual document. The file would reveal collaboration between the National Security Agency (NSA) and giant internet corporations under a secret programme called Prism.

Poitras flew again to New York for what she imagined would be her meeting with a senior intelligence bureaucrat. The source then sent her an encrypted file. In it was the Prism PowerPoint, and a second document that came as a total surprise: “Your destination is Hong Kong.” The next day, he told her his name for the first time. Poitras knew that if she searched Snowden’s name on Google, this would immediately alert the NSA. Attached was a map, a set of protocols for how they would meet, and a message: “This is who I am. This is what they will say about me. This is the information I have.”

In mid-April, Greenwald received a FedEx parcel containing two thumb drives with a security kit allowing him to install a basic encrypted chat programme. Snowden now contacted Greenwald himself. “I have been working with a friend of yours ... We need to talk, urgently.” The whistleblower finally had a direct, secure connection to the elusive writer. Snowden wrote: “Can you come to Hong Kong?”

The demand struck Greenwald as bizarre. His instinct was to do nothing. He contacted Snowden via chat. “I would like some more substantial idea why I’m going and why this is worthwhile for me?”

Over the next two hours, Snowden explained to Greenwald how to boot up the Tails system, one of the securest forms of communication. Snowden then wrote, with what can only be called understatement, “I’m going to send you a few documents.”

Snowden’s welcome package was around 20 documents from the NSA’s inner sanctuaries, most stamped Top Secret. At a glance, it suggested the NSA had misled Congress about the nature of its domestic spying activities, and quite possibly lied. “It was unbelievable,” Greenwald says. “It was enough to make me hyperventilate.” Two days later, on May 31, Greenwald sat in the office of Janine Gibson, the Guardian US’s editor in New York. He said a trip to Hong Kong would enable the Guardian to find out about the mysterious source. Stuart Millar, the deputy editor of Guardian US, joined the discussion. Both executives agreed that the only way to establish the source’s credentials was to meet him in person. Greenwald would take the 16-hour flight to Hong Kong the next day. Independently, Poitras was coming along, too. But Gibson ordered a third member on to the team, the Guardian’s veteran Washington correspondent Ewen MacAskill. The 61-year-old Scot and political reporter was experienced and professional. He was calm. Everybody liked him.

Except Poitras. She was exceedingly upset. As she saw it, an extra person might freak out the source, who was already on edge. “She was insistent that this would not happen,” Greenwald says. “She completely flipped out.” He tried to mediate, without success. However, at JFK airport, the ill-matched trio boarded a Cathay Pacific flight. Poitras sat at the back of the plane. She was funding her own trip. Greenwald and MacAskill, their bills picked up by the Guardian, were farther up in Premium Economy. As flight CX831 took off, there was a feeling of liberation. Up in the air, there is no internet — or at least there was not in June 2013. Once the seatbelt signs were off, Poitras brought a present they were both eager to open: A USB stick. Snowden had securely delivered her a second cache of secret NSA documents. This latest data set was far bigger than the initial “welcome pack”. It contained 3,000-4,000 items.

For the rest of the journey, Greenwald read the latest cache, mesmerised. Sleep was impossible: “I didn’t take my eyes off the screen for a second. The adrenaline was so extreme.” From time to time, Poitras would come up from her seat in the rear and grin at Greenwald. “We would just cackle and giggle like schoolchildren. We were screaming and hugging and dancing with each other up and down,” he says. Their celebrations woke up some of their neighbours; they didn’t care.

The first rendezvous was in Kowloon’s Mira hotel, a chic, modern edifice in the heart of the tourist district. Poitras and Greenwald were to meet Snowden in a quiet part of the hotel, next to a large plastic alligator. They would swap pre-agreed phrases. Snowden would carry a Rubik’s cube. Everything Greenwald knew about Snowden pointed in one direction: That he was a grizzled veteran of the intelligence community. “I thought he must be a pretty senior bureaucrat,” Greenwald says. Probably 60-odd, wearing a blue blazer with shiny gold buttons, receding grey hair, sensible black shoes, spectacles, a club tie. Perhaps he was the CIA’s station chief in Hong Kong. The pair reached the alligator ahead of schedule. They sat down. They waited. Nothing happened. The source did not show. Strange.

If the initial meeting failed, the plan was to return later the same morning. Greenwald and Poitras came back. They waited for a second time.

And then they saw him — a pale, spindle-limbed, nervous, preposterously young man. He was dressed in a white T-shirt and jeans. In his right hand was a scrambled Rubik’s cube. Had there been a mistake?

The young man — if indeed he were the source — had sent encrypted instructions as to how the initial verification would proceed:

Greenwald: What time does the restaurant open?

The source: At noon. But don’t go there, the food sucks ...

Greenwald — nervous — said his lines, struggling to keep a straight face. Snowden then said simply: “Follow me.” The three walked silently to the elevator. They rode to the first floor and followed the cube-man to room 1014. Optimistically, Greenwald speculated that he was the son of the source, or his personal assistant. If not, then the encounter was a waste of time, a hoax ...

— Guardian News & Media Ltd

Part 4 of 5 will be published tomorrow