Miss Baxter did the deed. After leaving Baxter to hold the bag after the jewel theft, Peter Coyle changes his name to Green to avoid any risk of being caught. He works his way through the service in various households until he is hired by Tony Gillingham. Miss Baxter, runs into Coyle, now Green, in London, confronts him, and in frustration and anger, gives him a shove, causing him to fall under the bus. This is how she knows Anna and Mr. Bates are innocent.