In the 90s, Austria was rocked by a four-year long series of letter bombs. Several intellectuals, left-leaning persons or prominent immigrants received letter bombs, some were killed or maimed, among them the former mayor of Vienna. Apparently the sender was a neo-nazi.
The story is told from the view-point of a police psychologist, who tries to track the letter bomber by getting a psychological profile of him. Actually, the letter bomber was not caught because of the profiler's work, but the profiler had delivered a surprisingly good description.
The movie is made a bit in "Columbo" style: the criminal is known from the beginning, and the watcher sees the noose tighten slowly. On the other hand there is more than a detective story behind it. There is an invisible criminal, who will strike again and again, and the big issue is "how can we figure out what he will do next, and how can we outsmart him?"
Some details in the movie are fictitious, but any Austrian should remember the letter bomber Franz Fuchs and how he was caught.