I remember reading (1) on the occasion of the latest criminal complaint against Rumsfeld in Germany, that since the statute for criminal prosecution of war crimes (Völkerstrafgesetzbuch) came into force in 2002, in 58 cases a criminal complaint was filed but no case lead to an prosecution (I recollect at least one case of an Ugandan who was arrested pending the prosecutor’s decision not to prosecute). That cannot solely be due to considerations of political expediency on the prosecutors’ part because there is a mechanism in German criminal procedure to sue an unwilling prosecutor’s office in order to compel them to prosecute.
(1) recollect reading in a reputable German newspaper - sorry no cite.
We are still on the I s . Z will ahave to wait a while.