The Shimoyama incident (下山事件 Shimoyama jiken) was an incident in Japan in 1949, which involved the disappearance and death of Sadanori Shimoyama (下山 定則 Shimoyama Sadanori, born July 23, 1901), the first president of Japanese National Railways. He disappeared on his way to work, July 5, 1949, and his body was found the next day. Following the discovery of his body, the media offered conflicting explanations involving suicide and murder, while the police did not publicly report the results of their investigation, which was then ended. The Mitaka incident, the Matsukawa incident, and the Shimoyama incident occurred within one month of one another, and together are known as JNR's Three Big Mysteries.