The coauthor of the Washington Post’s bombshell story on the National Security Agency’s PRISM surveillance program is a long-time activist filmmaker who has railed against U.S. counterterrorism policies put into place after the Sept. 11 attacks. Filmmaker Laura Poitras, who shared the lead byline with former Post journalist Barton Gellman on the paper’s front-page NSA story, is not on the Post’s staff and is not a print reporter. Poitras has criticized the “illegal” Guantanamo Bay detention facility, described enhanced interrogation techniques as “legalized torture,” and criticized the intelligence community’s surveillance methods in her films and public comments. While traditional media...