Den fjärde mannen S01E01 - Part 1

In 1989, the murder of Kjell Ohlsson, in Stockholm, Sweden, has Investigators grasping at tracks to follow to a motive and a murderer. But nothing pans out that gets them any closer. In present day Stockholm, an Investigation into the circumstances surrounding the 1975 attack on the West German Embassy is opened up by the Swedish Security Police; to discover who in Sweden helped the revolutionaries responsible. What is the connection between these two investigations?