Bill Binney worked at the National Security Agency [for] nearly three decades as one of its leading crypto-mathematicians. He then became one of its leading whistleblowers. The NSA is overseen by Congress, the courts and other government departments. It's also supposed to be watched from the inside by its own workers. But over the past dozen years, whistleblowers like Binney have had a rough track record. Those who tried unsuccessfully to work within the system say Edward Snowden - the former National Security Agency contractor who shared top-secret documents with reporters - learned from their bitter experience. For Binney, the decision to quit the NSA and become a whistleblower began a few weeks after the terrorist attacks of Sept. 11, 2001, when he says he discovered the spy agency had begun using software he'd created to scoop up information on Americans - all without a court order. I had to get out of there, because they were using the program I built to do domestic spying, and I didn't want any part of it, I didn't want to be associated with it," he says. "I look at it as basically treason. They were subverting the Constitution." Binney says he and two other NSA colleagues who also quit tried sounding the alarm with congressional committees. But because they did not have documents to prove their charges, nobody believed them. Snowden, he says, did not repeat that mistake. "He recognized right away, it was very clear to me, that if he wanted anybody to believe him, he'd have to take a lot of documentation with him - which is what he did," Binney says.