Snowden signed a non-disclosure agreement to get the Federal security clearance

[MADem]

132. He is an old man who was operating under very different rules.

I don't think he was working under a terribly robust security agreement. He never had to sign the type of documentation that has been common since the Walker spy scandal and Pollard and Hansen, etc. There was never any dedicated OPSEC or nondisclosure training, either way back when that unambiguously spelled out his responsibilities, and the espionage law also had a lot of wiggle room in it. And he--or a third party--wasn't going to gain from his disclosure.

Despite strong evidence that Ellsberg copied classified government documents and gave them to the press, the government's case against him was not without problems. Federal espionage laws targeted most clearly those who provided foreign governments with classified information, not those who gave documents to members of Congress or the American press. Even the theft charge raised issues, as the defense would argue that Ellsberg--unlike the vast majority of "thieves"--sought no personal advantage, or advantage for any third party, from copying documents. The defense could also raise issues about whether an historical record, such as the Pentagon Papers, could properly be classified "top secret." Still, as defense attorney Leonard Boudin told Ellsberg, "Let's face it, Dan. Copying seven thousand pages of top secret documents and giving them to the New York Times has a bad ring to it."
http://law2.umkc.edu/faculty/projects/ftrials/ellsberg/ellsbergaccount.html

Of course, the icing on the cake that put Ellsberg in the Get Out of Jail Free Zone was the egregious misconduct and blatant criminality by Nixon's White House--they broke into Ellsberg's shrink's office, they thought about having the guy killed; it was just very much Over The Top and tainted the proceedings completely. Had they played it straight, though, and not tried to pervert the course of justice, Ellsberg still may have walked--a jury nullification wasn't beyond the realm of possibility.