Citizenfour, the new documentary from acclaimed filmmaker Laura Poitras, director of The Oath and My Country, My Country, has incredible access to NSA whistleblower Edward Snowden, produced as it is by a central protagonist in his story. It is no small achievement to show the human cost of blowing the whistle as vividly as Poitras’ film does without obscuring the importance of the message. No viewer is likely to come away from Citizenfour unconvinced of the gravity of mass surveillance, or that systems of support for truthtellers are so sorely needed – and that, despite enormous risks, conscientious individuals will continue to come forward to inform the public.

The centerpiece of Citizenfour is a sequence that takes up half its running time, shot in the Hong Kong hotel room where Edward Snowden first met the journalists who would bring his revelations to world attention. In a small room at the Mira, Edward Snowden explains in calm and lucid terms why he decided to risk his life and liberty to expose international mass surveillance, unambiguously in the interests of the public. In a matter of days, he and the three journalists in the room – Laura Poitras, Glenn Greenwald and Ewen MacAskill – pull together the initial reports that dominated headlines in the summer of 2013: the Verizon court order that demonstrated the existence of domestic bulk collection, the NSA’s PRISM access to online service providers’ data, GCHQ’s extraordinarily broad TEMPORA data collection and, of course, finally the identity of the whistleblower himself.

In the lead-up to the sequence in Hong Kong, we see just how much our understanding of the NSA’s activities owes to whistleblowers. Poitras shows William Binney’s attempts to first build privacy protections into the ThinThread collection programme, and then to make its civil liberties infringements known. We also see arguments in the EFF’s long running anti-surveillance legal action, Jewel v NSA, launched back in 2008 as a consequence of AT&T whistleblower, Mark Klein’s disclosures. This sequence shows the limits of legal activism in the face of state secrets privilege and the other maneouvres the government can employ when facts are not in the public domain. By providing the documents that enable such actions to continue, Edward Snowden has in a very real sense built on the contributions of previous whistleblowers.

Just as Mark Klein’s disclosures made the initial stages of Jewel v NSA possible, the film indicates the range of consequences of Snowden’s revelations. The revelations have produced more real-world impact than could fit in any two hour documentary, but we see scenes from the EU and Brazilian investigations into mass surveillance. Bill Binney comes back into frame, this time to testify to the ongoing Bundestag investigation into surveillance. The film conveys the feeling that there’s going to be a lot more to come – and Courage’s official Edward Snowden support site will continue to track those developments here.

One of the most important messages of the film is left implicit: as viewers, we are made very aware of the risks Edward Snowden took. Poitras’ camera captures Snowden’s reaction to truly extraordinary circumstances. Even as we see his bravery in contemplating his own likely apprehension and imprisonment – he is surprisingly calm throughout – Edward Snowden is still visibly unnerved when he learns that his girlfriend Lindsay Mills has had to deal with a visit from the authorities. The Edward Snowden in Poitras’ film is a remarkable individual, but also very human one with very human fears about what might happen to him. When we see assistance begin to arrive – some days into his stay in Hong Kong, Edward Snowden is shown speaking to local lawyers over the telephone – we see how those efforts had to be improvised in the midst of international press attention and with US agents on their heels. The actions that actually saved Edward Snowden and brought him to safety of asylum in Russia happen off-screen, but a short shot of Julian Assange nods to this parallel narrative being planned simultaneously to the action Laura Poitras was able to film. Overall, the film serves as a striking reminder of the vital importance of reliable whistleblower protection and the risks involved in providing it.

Citizenfour concludes on two notes of optimism: first, we see that here is life after blowing the whistle and that Edward Snowden is leading an ordinary life in Russia with Lindsay Mills, free to continue to participate in the international debate he kick-started. We also see that others are coming forward. Greenwald is shown meeting Edward Snowden in another hotel room, this time in Moscow, telling him about a new source who was inspired by Snowden to blow the whistle.

Laura Poitras’ film shows us that that it is possible for truthtellers to escape prosecution under unjust laws and and an unconscionably long prison sentence. The US government tried to set an example of Chelsea Manning with an extremely long prison sentence as a deterrent; by protecting Snowden before he was discovered, those who helped him have set an example of their own to stand up for whistleblowers no matter the cost. But the film should also remind us of the need to ensure that systems and support networks are in place for future Snowdens to avoid prison. That’s spurred in part by Edward Snowden, and partly by what’s happened to his forerunners, like Bill Binney, or like Courage Advisory Board member Thomas Drake, another NSA truthteller. Drake worked for the NSA until 2006, when he blew the whistle on warrantless wiretapping. The US government charged him with espionage, threatening decades in prison, and ran him bankrupt fighting the case before dropping the major charges just before trial, leaving him out of work, out of money, and out of a reputation he spent his life building. Drake, like Snowden, could’ve used a well-resourced and well-prepared support system ready to defend him on every front. That’s what Courage is doing: both by crowdsourcing the legal defence for named truthtellers like Edward Snowden and by intervening as early as we can with a new fund for sources who find themselves under investigation and unable to go public, along with other plans as we grow to offer assistance and protection to truthtellers.

That Edward Snowden was protected even in such an extreme situation underscores how important it is for organisations like Courage to be prepared well earlier: to have lawyers and activists prepared to drop everything and protect a source before the government comes knocking on their door. The next Snowdens should have the kind of security they need waiting for them, so all they need to do is blow the whistle.