Characters who are classed as being Lawful Evil may follow a set of rules that they are bound to, but this doesn't mean that they aren't still capable of committing some truly heinous acts in accordance with the law. A lot of the time, characters who fit this moral description will stretch the boundaries of these rules as far as they can go to enact as much chaos as possible, without actually looking "bad" as a person, since they're still technically following the same laws as much as anyone else.