Chayanon was in a group of 12 AFS students and a teacher who left Yekaterinburg for Izhevsk on a night train after attending a language and cultural camp.
The train left Yekaterinburg at 8.28pm on Nov 30 and was scheduled to arrive Izhevsk on Dec 1 at 08.01am.
At 4am, the teacher saw Chayanon was not in his bed and a subsequent search failed to locate him. The teacher then asked staff to stop the train and look for him. They later found Chayanon’s body in the train’s vestibule space.
An initial investigation found no sign of violence and his money and belongings were still in his compartment.
Investigators are working on the theory that he fell in the vestibule space, the Criminal Investigation Division of Russia's Investigative Committee reported.