I think that it's not actually possible to know anything, and your only real options after recognising that are to reject the pursuit of truth entirely or fall back onto probabilistic models instead of binary beliefs. Not knowing whether or not Snowden is a CIA asset leads me to the question, "how likely is it that Snowden is a CIA asset?" As to why we should care, here's another question: "if Snowden were a CIA asset, how would that change my future behavior?" If it wouldn't change your future behavior, carry on not caring. If it would, then ask yourself "given that I may be wrong about Snowden being a CIA asset, which way would I rather err for an optimal risk/reward ratio?" Then you consider all three answers, and decide how to act in the future despite never actually coming to a conclusion about whether Snowden is a CIA asset. Maybe you think the risk of him being an asset is so low that you don't mind risking the chance that he isn't, or maybe you think it's reasonably likely that he could be an asset while not believing that your personal risk from being wrong is worth worrying about. Or, maybe you change your behavior.