How does the NSA offer amnesty anyway? Is it not the Justice Department that would bring charges in this situation? It's like the family of a murder victim offering amnesty to the murderer... it's not really up to them.
The NSA isn't offering amnesty. An NSA official is saying that he would recommend offering amnesty if doing so would assure no further leaks of the information Snowden has revealed. Presumably, the Justice Department would be the recipient (or among the recipients) of that recommendation.
"When you have eliminated the impossible, whatever remains, however improbable, must be the truth."