Und Jimmy ging zum Regenbogen (1971)

The son of an Argentine chemist travels to Vienna, to solve the murder of his father. Step by step, he realizes that his father was internationally entangled in secret service machinations and chemical weapon sales, and ends up in mortal danger himself. Meanwhile, he also realizes that there is no connection between his father's murderess and those dubious activities. Her motive for killing him goes back much futher, to a court hearing during the Third Reich...