Maryland v. King

In Maryland v. King, police arrested Alonzo Jay King, Jr. in 2009 on assault charges. After the arrest, and as part of the booking process, officers collected a DNA sample from King using a buccal swab, which means they rubbed the inside of his cheek to collect cells. Maryland law allowed DNA collection from people arrested for certain serious offenses.

King’s DNA profile was later compared with DNA evidence from an unsolved rape case. The comparison produced a match, and King was eventually charged and convicted in connection with that earlier crime. King challenged the DNA collection, arguing that taking his DNA without a warrant violated the Fourth Amendment.

The Maryland Court of Appeals agreed with King and ruled that the DNA collection was unconstitutional. The State of Maryland took the case to the Supreme Court of the United States.

The question in Maryland v. King was whether the Fourth Amendment allows police to take and analyze a cheek-swab DNA sample from a person who has been lawfully arrested for a serious offense, without first getting a warrant.

In plain terms, the Court had to decide whether DNA collection during booking is more like a routine identification procedure, such as fingerprinting and photographing, or whether it is an unconstitutional search because it reveals personal biological information and may help solve unrelated crimes.

The Supreme Court held that Maryland’s DNA collection procedure was constitutional under the Fourth Amendment when applied to a person lawfully arrested for a serious offense and processed into custody. The Court treated the cheek swab as a search, but found it reasonable under the circumstances.

The Court emphasized several points. First, King had already been lawfully arrested based on probable cause. Second, the DNA swab was a minimal physical intrusion. Third, the government has legitimate interests during booking, including accurately identifying the arrestee, assessing criminal history, making safe custody decisions, and determining risks connected to release or detention. The Court compared DNA identification to established booking tools like fingerprints and photographs, while recognizing that DNA is a more modern and powerful identification method.

The practical rule from Maryland v. King is that, at least for serious offenses covered by a valid statute, police may collect a cheek-swab DNA sample from a lawfully arrested person during booking without a warrant, so long as the collection is part of a lawful identification and booking process. The decision does not give officers unlimited authority to collect DNA from anyone they encounter. It rests on a lawful custodial arrest, a serious offense, and a regulated booking procedure.

For officers, Maryland v. King supports DNA collection during booking when the arrest is lawful, the offense qualifies under the governing DNA statute, and the agency follows the required procedures. The case is strongest when the DNA swab is handled like an identification step in the booking process, similar in purpose to fingerprinting, photographing, and checking records.

Officers should not read this case as permission to collect DNA casually in the field, during every detention, or from people who are not under lawful custodial arrest. The Supreme Court’s reasoning depended heavily on the fact that King had been arrested on probable cause and was being processed for a serious offense under Maryland’s statutory system.

Detectives should understand that DNA lawfully collected during booking may later produce a hit to evidence from an unsolved case. That was exactly what happened in Maryland v. King. But the legality of the collection depends on the front-end arrest and booking process being lawful. If the arrest is invalid, or if the statute or department policy is not followed, the resulting evidence may be vulnerable to suppression.

Supervisors should ensure that officers know which offenses qualify for DNA collection under current state law, who is authorized to collect the sample, how the sample must be documented, and what procedures apply if charges are later dismissed or the arrestee is not convicted. Those statutory details can vary by jurisdiction and need source verification under the applicable state law and agency policy.

For citizens and students, the key takeaway is that the Supreme Court balanced privacy interests against law enforcement identification needs. The Court allowed a limited DNA cheek swab after a lawful arrest for a serious offense, but it did not eliminate Fourth Amendment limits on searches involving biological information.