Edward Snowden says dishonest comments to Congress by the US intelligence chief were the final straw that prompted him to flee the country and reveal a trove of national security documents.
In an interview with Wired magazine over several days in Moscow, Snowden said he had been long been troubled by the activities of the National Security Agency, which employed him as a contractor.
But it was only when Director of National Intelligence James Clapper told lawmakers that the agency does "not wittingly" collect data on millions of American citizens that he was angry enough to act.
The magazine released the article online today, along with several new photographs of the once elusive Snowden, including a cover shot of the young technician lovingly cradling an American flag.
Snowden says he made his decision to leave his office in Hawaii and head to Hong Kong with secret documents on thumb drives after reading in March 2013 about Clapper briefing a Senate committee.
"I think I was reading it in the paper the next day, talking to coworkers, saying, can you believe this...?" Snowden says.
Following Snowden's sensational leaks about the scale of US global surveillance and how the NSA sucks up data on US users' phone calls, Clapper apologised to the Senate for his "erroneous" remarks.
Snowden told Wired that he had already thought about "whistle-blowing" several times over the previous few years.
Journalist Glenn Greenwald, who was later given the thousands of secret NSA files, has said Snowden contacted him anonymously in December 2012, three months before Clapper's briefing.
Snowden told Wired he had been troubled by other discoveries in his work with the agency, including that the NSA was spying on the pornography-viewing habits of political radicals.
"It's much like how the FBI tried to use Martin Luther King's infidelity to talk him into killing himself," he said.
"We said those kinds of things were inappropriate back in the '60s. Why are we doing that now?"
Snowden was also disturbed by the NSA's effort to massively speed up data collection with a secret data storage facility in Bluffdale, Utah, which scanned billions of phone calls, faxes, emails, computer-to-computer data transfers and text messages from around the world.
He told Wired he put off his plan to leak NSA secrets at the time of the election of President Barack Obama, hoping for a more open government.
But he became disenchanted with the president, and by 2013 was ready to spill the secrets he had acquired.
