Detective Kyosuke Kozu's Murder Reasoning II (1985)

Original title: 探偵・神津恭介の殺人推理2

Reportage writer Kenzo has made an interview appointment with Morishima, the mastermind behind the political and business world. On that day, Morishima is killed and a 200 million yen diamond is stolen. The diamond was brought by jeweler Kuhara to sell to Morishima. A woman named Maki who was present and disappeared immediately after the incident is suspicious. However, the site is a completely closed room. Kenzo's older brother, Matsushita, the chief of the investigation section, also shook his head...