Asimov invented a 4th law... the Zeroth law takes precedence, but only in robots sophisticated enough to reason it out.
What did Robocop introduce?
Well, if you haven't seen the movie I don't want to give it away, but trying to sum it up without spoilers: In the original movie (which is way better than the sequels), Robocop is programmed with a version of Asimov's three laws, but he also has a hidden fourth directive known only to his programmers, which only they can activate and which can be used to prevent him from executing his other directives consistently. There's also a robot which is programmed to enforce the law but is authorized to legally use lethal force, and thus it can be used to murder by misidentifying an innocent target as criminal.