The Guardian has added another partner to its reporting collaboration on the NSA files leaked by Edward Snowden.  Investigative reporting outfit ProPublica confirmed that it has been quietly working with The Guardian on a story on the subject and has recently joined with the New York Times as well.

From Buzzfeed:

The non-profit investigative reporting group ProPublica is among the media organizations with access to some NSA documents leaked by Edward Snowden, another suggestion that the reportorial investigation into the National Security Agency’s programs and practices is broader than previously known.

ProPublica, a source familiar with the situation said, is doing the lead reporting on one piece of the collaboration with the Guardian — which was the first to print Snowden’s revelations — and the New York Times, which BuzzFeed reported Friday had been brought in to work on one portion of the documents, which relate in some way to the NSA’s connections to its British counterpart.

ProPublica’s president, Richard Tofel, confirmed the collaboration in an email, and suggested the group has quietly been in the mix for some time:

“While we do not usually comment on stories before they are published, in light of what’s already appeared on this subject, we can confirm that we have for some time been working with the Guardian, and more recently also the New York Times, on a story based on documents provided by Mr. Snowden,” he said.

Buzzfeed notes that “sources declined to detail the exact publishing arrangement between the Guardian, the Times, and ProPublica.”

ProPublica’s headquarters are in New York, and the outlet’s focus has been on labor intensive investigative pieces since it first began publishing stories in 2008.  It was founded by former Wall Street Journal managing editor Paul Steiger. It is currently run by Stephen Engelberg, a former managing editor of The Oregonian and former investigative editor of The New York Times, and Richard Tofel, former assistant publisher of The Wall Street Journal.

Citing increased pressure from the UK government, The Guardian announced on Friday that it had struck a partnership with the New York Times to report on files leaked by Snowden pertaining to the UK Government Communications Headquarters (GCHQ).

The addition of the NY Times as a US partner came on the heels of recent incidents involving The Guardian in the UK, including the detention of Glenn Greenwald’s partner David Miranda, and the revelation that the UK government oversaw the destruction of the outlet’s hard drives containing Snowden’s documents.

The Independent published an article Friday in which it revealed the existence of a UK internet monitoring station in the Middle East as part of the government’s counter-terrorism surveillance operations.  While the article did not cite Snowden as a source, it indicated that the information was contained in Snowden’s leaked NSA documents, prompting criticism and suspicion from Snowden and Greenwald that the UK government itself leaked the information to The Independent.  That publication has caused many to wonder just how many outlets have access to Snowden’s materials, and whether or not the cache may have fallen outside the NSA leaker’s control.