It's a little bit more complicated. Because Kurnaz is a turkish citizen Turkey had been responsible for his return. They refused and Germany did not want to admit him because his residence permit had expired and he had not renewed it during his imprisonment in Guantanamo as required. This reason was given by Hans-Georg Maaßen, the head of the department responsible at the time in the Federal Ministry of the Interior and later head of the Office for the Protection of the Constitution before he became the CDU's far-right candidate