I can't find any statement of the German government anywhere declaring this "closed", much less that they "know who did it". (It'd also be a pretty weird statement to make, given the Swedes, who are leading the investigation since its their territory, only a few days ago formally confirmed that they could prove that explosives were used)

17th October (EDIT: or the days before, slightly conflicting info) apparently the German ships that took part in the first official inspection came back, but ... that's not "ending the investigation"!