I would hold on to the money for about a month and see if anything appeared on the news about it.. if I didnt hear anything FINDERS KEEPERS and I would pay all my debt off.
The reason I wouldnt call the cops is not because im a criminal.. but because they would most likely take it and it would end up in the evidence room... cops in my town are crooked for the most part (nothing against cops... Ive met many nice officers.. but the ones here are HORRIBLE, RACIST, and SCANDALOUS)