In 30 states, the police can collect DNA samples from arrestees to compare with national databases, without any finding of guilt. A recent report for the Pew Charitable Trust examines the practice, which on its face might seem to violate basic principles of “innocent until proven guilty.” The Supreme Court doesn’t think so: in 2013 it upheld the practice, saying taking samples at the time of arrest doesn’t violate the Fourth Amendment’s protection against unreasonable searches and seizures. “Taking and analyzing a cheek swab of the arrestee’s DNA is, like fingerprinting and photographing, a legitimate police booking procedure.” (Maryland v. King, a 5-4 decision with the unusual dissenting group of Scalia, Ginsburg, Sotomayor, and Kagan)