The greatest cheat, thief, and murderer you are likely to ever meet face to face, as well as to get to know pretty well from up close, is your own fucking self.

Addendum (April 11, 2016)

Of course, the only human you are ever likely to get to know pretty well from up close is yourself. Human intelligence has evolved so as to remain a mystery to all the others while attempting to unravel their mysteries in turn. Even unraveling many a mystery of one’s own may turn into a formidable feat for a human of exceptional intelligence. Still, your best chances are squarely with yourself. And the entire human species is in your body, and especially in your brain. Only consider all the cheats, thieves, and murderers among your own ancestors… Remember, humans have not changed very much over hundreds and perhaps even thousands of generations. Good luck!