A tooth for a tooth

Uproar in a factory housing project in Duisburg: it is scheduled for sale and demolition. Industrialist Grassmann regrets the fate of the residents, but he, too, is forced by economic necessity. One of those affected, Alf Krüger, first kills his family, then himself. What are the motives for the family tragedy? Despair over the forced eviction? But why did the meticulous accountant overlook his youngest child? And what was the humble man doing in Marseille shortly before his death?