The Simon Wiesenthal Center is expanding its poster and reward campaign in Germany in its push to track down Nazi war criminals before it is too late.

The center's top Nazi-hunter, Efraim Zuroff, said Monday that Operation Last Chance II, launched in July, resulted in tips on 108 possible suspects, primarily in Germany. He says so far four of those have developed into concrete cases being investigated by prosecutors, though no charges have yet been filed.

The center is offering up-to 25,000 euros ($34,000) for tips that lead to the arrest and conviction of war crimes suspects.

The campaign started with posters reading "late, but not too late" in Berlin, Hamburg and Cologne. Now another 2,500 posters are being distributed in Leipzig, Munich, Magdeburg, Rostock, Stuttgart, Dresden, Nuremberg and Frankfurt.