So this is probably just semantics, but can someone be "pardoned" when they have not yet been tried and found guilty of a crime? Until Snowden is tried and found guilty, he is innocent. What is there to exonerate at present?
"After Ford left the White House in 1977, he privately justified his pardon of Nixon by carrying in his wallet a portion of the text of Burdick v. United States, a 1915 U.S. Supreme Court decision which stated that a pardon indicated a presumption of guilt, and that acceptance of a pardon was tantamount to a confession of that guilt."