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Of course, the main reason is the change of law in the way Germany has brought Nazi war criminals to trial. The previous rules was that you'd have to have tangible evidence, and documentary evidence was not sufficient.

"The Last Of Nazi War Convictions Will Not End Fight Against Anti-Semitism". "Weekend Edition Saturday" with Linda Wertheimer, www.npr.org. February 13, 2016.
Of course, the main reason is the change of law in the way Germany has brought Nazi war criminals to trial. The previous rules was that you'd have to have tangible evidence, and documentary evidence was not sufficient.