Wow, mind = blown. You could perform binary search on the sewers to find a criminal. Hah, that would be ridiculous if that was possible.

There were some indications that we attempted a focused attempt in Pakistan during the hunt for Bin Laden.. From an interview with the Bureau Chief of Time who wrote the full detail story about how it went down:

> CROWLEY: Right. Unfortunately, Allison's language had to be a little bit cryptic. They couldn't confirm exactly what they had done, but he writes that in some of the option they consider were testing. It's not pleasant testing the sewage in the town for genetic markers, and then, another was this UAV. Actually, it wasn't an eagle size UAV. It's much smaller.

http://www.cnn.com/TRANSCRIPTS/1204/26/sp.02.html

Well, the Monterey Bay Aquarium does species counts using water sampling and searching DNA[1] so something similar might be possible to search for s specific individual signature.

[1]http://www.washington.edu/news/2014/01/15/dna-detectives-abl...