Judge Ford does not think anyone is in the coffin. She thinks it is a wax dummy.
Everyone assumes that billionaire Sam Westing died. However Judge Ford thinks that Samuel Westing was not in the coffin at all. She thinks it was a wax dummy made to resemble Sam Westing, whose appearance changed after the accident. She realizes that Sam Westing may not really be dead, and the body and the coffin are just part of the game and designed to throw off the heirs off track.
In the end, Turtle puts the clues together and determines that not only is Sam Westing alive, meaning that it was not his body in the coffin, but he has actually been there the whole time, as Sandy McSouthers the doorman. Turtle thus wins the game and becomes the heir to the Westing fortune.