Detailed records of the investigation into the so-called Shimoyama Incident of 1949, in which the president of the Japanese National Railways mysteriously died, were recently found by the family of a late JNR official.

Historians say the file, found among the belongings of Takeshi Yamaguchi, an official of the JNR security headquarters who probed the case, may provide some clues to the shady aspects of Japan under the Allied Occupation, which was riddled with mysterious incidents.

But the files themselves seem to shed no new light on the mystery.