Twenty-five years ago forensic investigators needed a blood or semen stain the size of a dime to extract the DNA of a suspect. In the 1990s they needed a speck. Today they need what can’t be seen—as few as 70 of the 400,000 skin cells we shed each day. “Touch” or “trace” DNA has typically been used to investigate violent crimes. In 2008 a lab in Virginia extracted the DNA of a still-unidentified male from the long johns JonBenet Ramsey wore on the night of her death. Last year police in Wasatch County, Utah arrested a suspect for a 1995 murder after obtaining DNA from a cigarette he had discarded while officers were tailing him. The sample matched trace DNA recovered from granite rocks the killer used to bludgeon his 17-year-old victim.
Buoyed by that type of success, investigators are now preserving DNA from crime scenes where perps haven’t bled or ejaculated. In St. Petersburg, Florida police say trace DNA has led to arrests in 38 percent of burglaries over the past three years. In Houston about 75 percent of the more than 3,000 matches since 2008 have involved property crimes. In New York City about a third of DNA cases are related to property crimes.
Because discarded skin cells are dead, scientists believe that sweat, which picks up free-floating strands as it moves through pores, is the key to trace-DNA readings. A scientist needs about a nanogram of DNA to work up a profile. Holding a glass for 60 seconds yields about half that, while touching fabric or wood for a minute is more than sufficient, as is rubbing cotton against a palm or finger for 15 seconds. The more pressure and friction applied, the more likely DNA will be left. The rougher the surface, the more cells will stay. Besides rocks, investigators have obtained trace samples from pistol grips, pocket linings, asphalt, shoestrings and a victim’s tongue.
Skin cells are easily transferred, so one can’t assume that finding a person’s DNA on an object means he or she touched it. One investigator swabbed his own hand after shaking hands at a party, and a lab was able to extract the DNA of two of the people he’d met. There is a risk that juries will fail to heed that disclaimer and innocent people will be convicted based on cells that migrated to a stolen item or a murder weapon. The fact that a person can be tagged so easily perhaps makes the report that Madonna takes a cleanup crew on tour with her sound less bizarre. “We can only enter [her dressing room] after her sterilization team has left,” a promoter in Portugal told the Daily Mirror. “There will not be any of Madonna’s DNA, any hair or anything.”
TURNOFFS: HOW TO ACHIEVE TOTAL ONLINE PRIVACY
British software developer Robb Lewis earlier this year launched justdelete.me after seeing tweets about the difficulty of closing a Skype account. He ranks dozens of sites on how hard they are to leave without a trace. Among your friends for life: Blogger, Gawker, GoDaddy, Netflix, Pinterest and Starbucks. The tough but possible include Amazon, Craigslist, iTunes, Pandora and Ticketmaster. To return to your pre-1994 existence, here‘s how to unplug from four popular services.