In a pickle is incorrect. There were 12 stab wounds on the body. The whole point is that they were like Judge and Jury (Hence 12 people). There were 13 people on the train as well as Poirot but the Husband and wife stabbed him together. Poirots verdict to the police was that Ratchett was killed by an assasin who then escaped in the snow.
The kidnapping story was based on the Lindberg kidnapping in the US