Maryland v. King
The Supreme Court ruled that police may take a DNA sample from someone arrested for a serious crime as part of routine booking, just as they take fingerprints and photographs, without needing a warrant or any suspicion that the DNA will solve a crime.
The 5-4 decision lets a rape conviction stand that was built on a DNA match discovered after a Maryland man was booked on an unrelated assault charge, and it clears the way for the many state and federal DNA-collection laws already in place for arrestees.
“When officers make an arrest supported by probable cause to hold for a serious offense and they bring the suspect to the station to be detained in custody, taking and analyzing a cheek swab of the arrestee’s DNA is, like fingerprinting and photographing, a legitimate police booking procedure that is reasonable under the Fourth Amendment.”
The Court's central holding on why DNA swabbing of arrestees is constitutional.
How it got here: A Maryland trial court upheld the DNA law and King was convicted of rape; Maryland's highest court set aside the conviction, finding the DNA collection unconstitutional, and the State asked the Supreme Court to review that ruling.
The Case in Depth
What happened
In 2003, an unidentified man raped a woman in Salisbury, Maryland, leaving behind a DNA sample. In 2009, Alonzo King was arrested in an unrelated matter for threatening people with a shotgun. As part of routine booking, officers swabbed the inside of his cheek for DNA under Maryland's DNA Collection Act, and the sample matched the 2003 rape evidence, leading to his rape conviction.
The question before the Court
Can police take a DNA sample by cheek swab from someone arrested for a serious crime, as a routine part of booking, without a warrant or individual suspicion?
The Court's answer
Yes — the Court ruled that once someone is validly arrested for a serious offense and brought into custody, taking a cheek-swab DNA sample as part of routine booking is a reasonable search under the Fourth Amendment, no different in kind from fingerprinting or photographing. No warrant or individualized suspicion is required.
The Court weighed the government's strong interest in accurately identifying people it takes into custody — including their criminal history, danger to others, and flight risk — against the minimal physical intrusion of a quick, painless cheek swab. Because the intrusion is so slight and the identification interest so significant, the balance favored the State, and King's rape conviction, built on the DNA match found through this booking procedure, was allowed to stand.
Curious how the Court got there? See the step-by-step legal reasoning →
Why it matters
People arrested for serious offenses across dozens of states can now expect a cheek swab alongside fingerprinting and photographing during booking, with their DNA profile entered into a national database and checked against unsolved crimes. Convictions resting on such DNA matches, like the one in this case, remain valid, and states are unlikely to face further Fourth Amendment challenges to arrestee DNA laws.
What changes now
This is a final merits decision, not a temporary order. King's rape conviction stands, and the Maryland DNA Collection Act's arrestee-testing provisions remain in effect. The ruling also validates similar DNA-collection statutes in the roughly 28 other states and the federal government that had adopted comparable arrestee DNA laws, though future disputes over different DNA uses or less serious offenses could still be litigated.
What this does not decide
The Court limited its holding to arrests for serious offenses supported by probable cause and to DNA testing used only for identification, not for other purposes like predicting disease. The dissent argued this limitation to 'serious offenses' is not logically sustainable, but the majority did not decide the constitutionality of DNA collection for minor offenses like traffic violations.
Concurrences and dissents
Dissent — Justice Scalia
Justice Scalia argued that suspicionless searches are only permitted when their purpose is something other than ordinary crime-solving, and that Maryland's actual DNA testing process — delayed until after arraignment, checked against unsolved crimes rather than a database that could confirm identity, and governed by a statute listing crime investigation as its purpose — shows the swab was really used to solve crimes, not identify King. He would have held the search unconstitutional and warned the ruling has no logical stopping point short of DNA testing for any arrest, including minor offenses.
How the Court got there
The legal reasoning, step by step
- The Court first established that swabbing the inside of a person's cheek to collect DNA counts as a 'search' under the Fourth Amendment, even though the physical intrusion is minor and does not go beneath the skin.
- Because King was already lawfully in police custody on probable cause for a serious offense, the Court held that the ordinary requirement of a warrant is greatly diminished, and the search is instead judged by 'reasonableness' — weighing the government's interest against the degree of privacy intrusion — rather than requiring individualized suspicion that the swab would reveal evidence of a specific crime.
- Applying that balancing test, the Court found a well-established government interest in accurately identifying people taken into custody, including their criminal history, potential danger to jail staff and other detainees, flight risk, and information relevant to bail decisions.
- The Court treated DNA identification as an advance on the same footing as historical booking practices like photographing and fingerprinting arrestees, reasoning that any extra intrusion beyond fingerprinting is minimal while the accuracy gained is far greater.
- On the privacy side of the balance, the Court noted that the specific DNA markers used (the CODIS loci) come from 'junk' DNA that does not reveal genetic traits, and that Maryland law restricts DNA testing to identification purposes only, which further limited the privacy cost.
- Weighing the strong identification interest against the minimal, statutorily-limited intrusion, the Court concluded that the cheek swab was a reasonable search when performed as a booking procedure following a valid arrest for a serious offense.