^ FWIW, our forensic techs told us that extracting DNA from a cigarette butt is extrememly difficult (and time consuming and expensive) and they only do it for serious crimes.... murders, kidnapping, etc. They credit CSI for making it appear efficient and failsafe.
How do I know?
I worked a burglary about 6 months ago and I found a cigarette butt on the floor of one of the bathrooms. The homeowners said none of them smoked, so I collected it for evidence. Then I got an earful from the forensic techs. Seemed like a good idea to me.