It isn't just "widely believed", it is something he admitted to doing. I am not sure why you are being downvoted for saying it.
>For the first time, Snowden has admitted he sought a position at Booz Allen Hamilton so he could collect proof about the US National Security Agency's secret surveillance programmes ahead of planned leaks to the media.
>"My position with Booz Allen Hamilton granted me access to lists of machines all over the world the NSA hacked," he told the Post on June 12. "That is why I accepted that position about three months ago."
>...Asked if he specifically went to Booz Allen Hamilton to gather evidence of surveillance, he replied: "Correct on Booz."[1]
Coworkers started to become suspicious of his intentions years earlier when he was with the CIA.
>Just as Edward J. Snowden was preparing to leave Geneva and a job as a C.I.A. technician in 2009, his supervisor wrote a derogatory report in his personnel file, noting a distinct change in the young man’s behavior and work habits, as well as a troubling suspicion.
>The C.I.A. suspected that Mr. Snowden was trying to break into classified computer files to which he was not authorized to have access, and decided to send him home, according to two senior American officials. [2]
The next sentence in that linked article states the documents leaked were from Booz Allen. He didn't have any proof to leak until he took the job. Therefore "he took the job at [Booz Allen] specifically so he could figure out what they were doing wrong and leak it." That is a fact. We don't know when he became intent on trying to whistleblow and whether it was while he was with the CIA or Dell, but it was clearly before working at Booz Allen. He never worked directly at the NSA.
>For the first time, Snowden has admitted he sought a position at Booz Allen Hamilton so he could collect proof about the US National Security Agency's secret surveillance programmes ahead of planned leaks to the media.
>"My position with Booz Allen Hamilton granted me access to lists of machines all over the world the NSA hacked," he told the Post on June 12. "That is why I accepted that position about three months ago."
>...Asked if he specifically went to Booz Allen Hamilton to gather evidence of surveillance, he replied: "Correct on Booz."[1]
Coworkers started to become suspicious of his intentions years earlier when he was with the CIA.
>Just as Edward J. Snowden was preparing to leave Geneva and a job as a C.I.A. technician in 2009, his supervisor wrote a derogatory report in his personnel file, noting a distinct change in the young man’s behavior and work habits, as well as a troubling suspicion.
>The C.I.A. suspected that Mr. Snowden was trying to break into classified computer files to which he was not authorized to have access, and decided to send him home, according to two senior American officials. [2]
[1] - http://www.scmp.com/news/hong-kong/article/1268209/snowden-s...
[2] - http://www.nytimes.com/2013/10/11/us/cia-warning-on-snowden-...