The Snowden case is an interesting example. He went out of his way to get access to information, going so far as to transfer into a role that had more access (I don’t recall all the details but I remember that much). Every company has some category of employee whose job it is to ensure enforcement of policies, for instance, and if these people set out to subvert the system you should expect them to be able to do so. The watching watchers onion does eventually run out of skin (and it’s not even that deep most places).

The right person with the right access can do a tremendous amount of damage. 14 years ago some servers I was hired to maintain (marketing sites for a gambling site out of Costa Rica) were wiped out as part of an inside job: http://boston.conman.org/2004/09/19.1

Who watches the watcher indeed.