Exactly... IIRC, wasn't the actual story a murder mystery? A robot apparently murders a human, and the whole story revolves around solving the mystery of whether or not the robot did it, and if it did, how it did it without violating the Three Laws.
No robot armies that I recall, though it has been a long time...
No, some of his books had similar premises... I'm not sure a robot ever actually murdered a human. Maybe one, but I don't recall. Usually turned out to be a human trying to frame a robot.