Though suspicions that a new source within the U.S. government's national security apparatus has been leaking classified and sensitive documents to some of the same journalists that have been reporting on the documents leaked by NSA whistleblower Edward Snowden, not until the premiere of Laura Poitras' new documentary film on the subject this weekend have those suspicions been confirmed by any of the journalists with direct knowledge of the facts.

“They can stomp me if they want to, but there will be seven more to take my place.” —Edward Snowden, in 'Citizenfour'However, in a dramatic revelation for those who have now seen 'Citizenfour'—which debuted at the New York Film Festival on Friday night where it received a standing ovation—a scene captured by Poitras shows award-winning journalist Glenn Greenwald quietly confirming to Snowden the existence of a secord source within the intelligence community who has been sharing highly-secretive information.

The official trailer of the film, also released Friday, gives a sense of the film's tenor and tone, but not much in way of exposé:

However, as journalist Ewan MacAskill, who himself played a key role in reporting on the Snowden affair and appears in the film, reports for the Guardian:

Towards the end of filmmaker Laura Poitras’s portrait of Snowden – titled Citizenfour, the label he used when he first contacted her – Greenwald is seen telling Snowden about a second source. Snowden, at a meeting with Greenwald in Moscow, expresses surprise at the level of information apparently coming from this new source. Greenwald, fearing he will be overheard, writes the details on scraps of paper. The specific information relates to the number of the people on the US government’s watchlist of people under surveillance as a potential threat or as a suspect. The figure is an astonishing 1.2 million. The scene comes after speculation in August by government officials, reported by CNN, that there was a second leaker. The assessment was made on the basis that Snowden was not identified as usual as the source and because at least one piece of information only became available after he ceased to be an NSA contractor and went on the run.

In his review of the film, executive director of the Freedom of the Press Foundation Trevor Timm places the existence of a second leaker in the context of Snowden himself as he describes the possible interplay between how the actions of one whistleblower may ultimately lead to motivating others to follow suit. Timm writes:

And in the end, Timm concludes:

...what the government has failed to grasp is that Chelsea Manning and Snowden’s leaks are not isolated incidents – or, at least they won’t be when we look back on this era 10 years from now. There are 5 million people with security clearances in this country, and many of them are part of a new generation that is far more critical of the blanket secrecy permeating government agencies than the old guard. It’s only now that we are finally starting to see the reverberations of Manning’s and Snowden’s whistleblowing. But one thing is for sure: there are many more potential whistleblowers out there, and if government officials do not move to make their actions more transparent of their own volition, then their employees may well do it for them.

The film will open in theaters nationwide on October 24th. A short sampling of film reviews of 'Citizenfour' that have emerged since Friday follow.

Edward Snowden documentary 'Citizenfour' jolts film world (Steven Zeitchik / Los Angeles Times):

Many documentaries seek to kick-start environmental movements, reverse death row sentences or even change legislative policy. But few come with the kind of ideological ambition of the Edward Snowden study "Citizenfour," a movie of grand scope that also tells an intimate personal story. The long-awaited documentary from Snowden chronicler Laura Poitras arrived with a bang at its world premiere at the New York Film Festival on Friday night, receiving a rare festival standing ovation ahead of its theatrical release Oct. 24, when it could well jolt both the fall moviegoing season and the national conversation about privacy and security. Poitras, as some may recall, shot the 12-minute video of Snowden that went viral in June 2013 and made the National Security Agency contractor, at 29, perhaps the most important and polarizing figure since Daniel Ellsberg. "Citizenfour” is, in effect, that original video effort writ very large — a look at how Snowden came to the decision to pull back the curtain on the NSA's massive surveillance operation and what happened to him when he did. It is also, needless to say, a portrait of that operation itself.

Poitras' victorious film shows Snowden vindicated (Spencer Ackerman / Guardian):

The film leaves many questions unanswered, such as Wikileaks’ role in Snowden’s drama – Julian Assange is briefly on camera – and Snowden’s circumstances in the authoritarian Russia that has granted him asylum. But Citizenfour shows Snowden vindicated when the film confirms that Greenwald, Poitras and their investigative partner Jeremy Scahill are working with a new security whistleblower, one apparently inspired by Snowden. While understated, Snowden appears thrilled, even moved. Given the passions that the NSA disclosures have generated, it’s remarkable how tempered Citizenfour comes across. Reflecting a style Poitras seems to share with Snowden, it’s a quiet movie, its soundtrack a sinister digital throb, packed tight with questions about how we live freely in an unseen dragnet. One of its only boisterous moments comes when Snowden and Greenwald discuss the spirit animating both the reporting and Snowden’s decision to reveal himself. Greenwald describes it as “the fearlessness and the fuck-you”. That fearlessness attracted Snowden to Poitras, and it shows through her camera.

Information is a weapon that cuts both ways in Laura Poitras' extraordinary portrait of NSA whistleblower Edward Snowden (Ronnie Scheib / Variety):