In the case of the SIlk Road servers, only two accounts had full administrative privileges. One was for a remote user called "frosty" who was able to connect from a machine also named "frosty." As it happened, the laptop that law enforcement seized from Ulbricht at the time of his arrest was named "frosty" too. You get bonus points (though only a few) for guessing that Ulbricht was logged in as "frosty" on that laptop at the time of his arrest. In effect, his laptop had full administrative rights to the Silk Road operations.
Ulbricht's defense lawyer, Joshua Dratel, pointed out to the jury that any computer could be given the name "frosty," with a user account on it named "frosty." But like a lot of other evidence in the case, while not definitive proof, the ssh accounts were part of a bigger picture that were enough to convince a jury of his guilt.
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