On Feb. 26, 2013, the U.S. Supreme Court heard oral argument in Maryland v. King, a case that Justice Alito called "the most important criminal procedure case this Court had had in decades." The case involves the constitutionality of warrantless, involuntarily DNA collection from individuals who have been arrested for a felony, but not yet charged or convicted. It is uncontested that DNA collection constitutes a search for purposes of the Fourth Amendment. This case asks whether compelling such searches in the absence of a warrant, and the absence of a criminal conviction, is reasonable.
Maryland, together with 27 other states and the federal government, has statutorily mandated law enforcement to collect a DNA sample from certain individuals upon arrest. The DNA extraction happens not because the state has any articulated suspicion whatsoever that the search will produce evidence of criminality. Were that so, the state could get a warrant to compel a DNA sample. Instead, the law requires arrestees to submit to DNA collection (typically by a buccal swab) based merely on the fact of the arrest. It is done so that law enforcement can analyze the DNA sample and compare it to the thousands of DNA profiles already in state and federal databases, in the hopes that the arrestee's DNA will match as-yet unidentified DNA evidence related to unsolved crimes.