Remember in Gattaca when detectives trying to solve a murder went around randomly taking DNA samples (via mouth swabs) from the general populace? No mention of "warrants" or "probable cause." As it turns out, Gattaca got the technology right, but not the means of gathering data. As this New York Times article explains, cops are becoming adept at grabbing snatches of DNA from suspects without their knowledge:
The two Sacramento sheriff detectives tailed their suspect, Rolando Gallego, at a distance. They did not have a court order to compel him to give a DNA sample, but their assignment was to get one anyway — without his knowledge.Other examples include getting DNA from a soda can (provided by interrogating officers) and a dinner glass.
Recently, the sheriff’s cold case unit had extracted a DNA profile from blood on a towel found 15 years earlier at the scene of the murder of Mr. Gallego’s aunt. If his DNA matched, they believed they would finally be able to close the case.
On that spring day in 2006, the detectives watched as Mr. Gallego lit a cigarette, smoked it and threw away the butt. That was all they needed.
Before you get too out of joint about such things, remember two bits of legal trivia. First, cops can lie and use subterfuge in order to get information out of you (with very few limits), so they're not really breaking new ground in terms of being sneaky. Second, the key inquiry when it comes to Fourth Amendment issues is whether someone has a "reasonable expectation of privacy," which is pretty hard to find in detritus left behind while wandering through the world.