DNA Tests of Arrestees

Supreme Court of the United States

Maryland v. Alonzo Jay King 

Decided June 3, 2013 – 569 U.S. 435


Justice KENNEDY delivered the opinion of the Court.

In 2003 a man concealing his face and armed with a gun broke into a woman’s home in Salisbury, Maryland. He raped her. The police were unable to identify or apprehend the assailant based on any detailed description or other evidence they then had, but they did obtain from the victim a sample of the perpetrator’s DNA.

In 2009 Alonzo King was arrested in Wicomico County, Maryland, and charged with first- and second-degree assault for menacing a group of people with a shotgun. As part of a routine booking procedure for serious offenses, his DNA sample was taken by applying a cotton swab or filter paper—known as a buccal swab—to the inside of his cheeks. The DNA was found to match the DNA taken from the Salisbury rape victim. King was tried and convicted for the rape. Additional DNA samples were taken from him and used in the rape trial, but there seems to be no doubt that it was the DNA from the cheek sample taken at the time he was booked in 2009 that led to his first having been linked to the rape and charged with its commission.




The Act authorizes Maryland law enforcement authorities to collect DNA samples from “an individual who is charged with … a crime of violence or an attempt to commit a crime of violence; or … burglary or an attempt to commit burglary.” ….If “all qualifying criminal charges are determined to be unsupported by probable cause … the DNA sample shall be immediately destroyed.” DNA samples are also destroyed if “a criminal action begun against the individual … does not result in a conviction,” “the conviction is finally reversed or vacated and no new trial is permitted,” or “the individual is granted an unconditional pardon.” 


Respondent’s DNA was collected in this case using a common procedure known as a “buccal swab.” “Buccal cell collection involves wiping a small piece of filter paper or a cotton swab similar to a Q-tip against the inside cheek of an individual’s mouth to collect some skin cells.” The procedure is quick and painless. The swab touches inside an arrestee’s mouth, but it requires no “surgical intrusio[n] beneath the skin,” and it poses no “threa[t] to the health or safety” of arrestees.


Respondent’s identification as the rapist resulted in part through the operation of a national project to standardize collection and storage of DNA profiles. Authorized by Congress and supervised by the Federal Bureau of Investigation, the Combined DNA Index System (CODIS) connects DNA laboratories at the local, state, and national level. All 50 States require the collection of DNA from felony convicts, and respondent does not dispute the validity of that practice. Twenty-eight States and the Federal Government have adopted laws similar to the Maryland Act authorizing the collection of DNA from some or all arrestees. At issue is a standard, expanding technology already in widespread use throughout the Nation.


It can be agreed that using a buccal swab on the inner tissues of a person’s cheek in order to obtain DNA samples is a search. Virtually any “intrusio[n] into the human body” will work an invasion of “‘cherished personal security’ that is subject to constitutional scrutiny.” The fact than an intrusion is negligible is of central relevance to determining reasonableness, although it is still a search as the law defines that term.


The Maryland DNA Collection Act provides that, in order to obtain a DNA sample, all arrestees charged with serious crimes must furnish the sample on a buccal swab applied, as noted, to the inside of the cheeks. The arrestee is already in valid police custody for a serious offense supported by probable cause. The DNA collection is not subject to the judgment of officers whose perspective might be “colored by their primary involvement in ‘the often competitive enterprise of ferreting out crime.’” “[T]here are virtually no facts for a neutral magistrate to evaluate.” Here, the search effected by the buccal swab of respondent falls within the category of cases this Court has analyzed by reference to the proposition that the “touchstone of the Fourth Amendment is reasonableness, not individualized suspicion.” 

***An assessment of reasonableness to determine the lawfulness of requiring this class of arrestees to provide a DNA sample is central to the instant case.



The legitimate government interest served by the Maryland DNA Collection Act is one that is well established: the need for law enforcement officers in a safe and accurate way to process and identify the persons and possessions they must take into custody.


The task of identification necessarily entails searching public and police records based on the identifying information provided by the arrestee to see what is already known about him. A DNA profile is useful to the police because it gives them a form of identification to search the records already in their valid possession. In this respect the use of DNA for identification is no different than matching an arrestee’s face to a wanted poster of a previously unidentified suspect; or matching tattoos to known gang symbols to reveal a criminal affiliation; or matching the arrestee’s fingerprints to those recovered from a crime scene. Finding occurrences of the arrestee’s CODIS profile in outstanding cases is consistent with this common practice. It uses a different form of identification than a name or fingerprint, but its function is the same.


Finally, in the interests of justice, the identification of an arrestee as the perpetrator of some heinous crime may have the salutary effect of freeing a person wrongfully imprisoned for the same offense. “[P]rompt [DNA] testing … would speed up apprehension of criminals before they commit additional crimes, and prevent the grotesque detention of … innocent people.” 

Because proper processing of arrestees is so important and has consequences for every stage of the criminal process, the Court has recognized that the “governmental interests underlying a station-house search of the arrestee’s person and possessions may in some circumstances be even greater than those supporting a search immediately following arrest.”


In sum, there can be little reason to question “the legitimate interest of the government in knowing for an absolute certainty the identity of the person arrested, in knowing whether he is wanted elsewhere, and in ensuring his identification in the event he flees prosecution.” To that end, courts have confirmed that the Fourth Amendment allows police to take certain routine “administrative steps incident to arrest—i.e., … book[ing], photograph[ing], and fingerprint[ing].” DNA identification of arrestees, of the type approved by the Maryland statute here at issue, is “no more than an extension of methods of identification long used in dealing with persons under arrest.” In the balance of reasonableness required by the Fourth Amendment, therefore, the Court must give great weight both to the significant government interest at stake in the identification of arrestees and to the unmatched potential of DNA identification to serve that interest.



By comparison to this substantial government interest and the unique effectiveness of DNA identification, the intrusion of a cheek swab to obtain a DNA sample is a minimal one.

The reasonableness of any search must be considered in the context of the person’s legitimate expectations of privacy. The expectations of privacy of an individual taken into police custody “necessarily [are] of a diminished scope.” A search of the detainee’s person when he is booked into custody may “‘involve a relatively extensive exploration,’” including “requir[ing] at least some detainees to lift their genitals or cough in a squatting position.”


In light of the context of a valid arrest supported by probable cause respondent’s expectations of privacy were not offended by the minor intrusion of a brief swab of his cheeks. By contrast, that same context of arrest gives rise to significant state interests in identifying respondent not only so that the proper name can be attached to his charges but also so that the criminal justice system can make informed decisions concerning pretrial custody. Upon these considerations the Court concludes that DNA identification of arrestees is a reasonable search that can be considered part of a routine booking procedure. 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 judgment of the Court of Appeals of Maryland is reversed.

Justice SCALIA, with whom Justice GINSBURG, Justice SOTOMAYOR, and Justice KAGAN join, dissenting.

The Fourth Amendment forbids searching a person for evidence of a crime when there is no basis for believing the person is guilty of the crime or is in possession of incriminating evidence. That prohibition is categorical and without exception; it lies at the very heart of the Fourth Amendment. Whenever this Court has allowed a suspicionless search, it has insisted upon a justifying motive apart from the investigation of crime.

It is obvious that no such noninvestigative motive exists in this case. The Court’s assertion that DNA is being taken, not to solve crimes, but to identify those in the State’s custody, taxes the credulity of the credulous. [T]he Court elaborates at length the ways that the search here served the special purpose of “identifying” King. But that seems to me quite wrong—unless what one means by “identifying” someone is “searching for evidence that he has committed crimes unrelated to the crime of his arrest.” 

[I]f anything was “identified” at the moment that the DNA database returned a match, it was not King—his identity was already known. (The docket for the original criminal charges lists his full name, his race, his sex, his height, his weight, his date of birth, and his address.) Rather, what the August 4 match “identified” was the previously-taken sample from the earlier crime. That sample was genuinely mysterious to Maryland. King was not identified by his association with the sample; rather, the sample was identified by its association with King. The Court effectively destroys its own “identification” theory when it acknowledges that the object of this search was “to see what [was] already known about [King].” No minimally competent speaker of English would say, upon noticing a known arrestee’s similarity “to a wanted poster of a previously unidentified suspect,” that the arrestee had thereby been identified. It was the previously unidentified suspect who had been identified—just as, here, it was the previously unidentified rapist. 

That taking DNA samples from arrestees has nothing to do with identifying them is confirmed not just by actual practice (which the Court ignores) but by the enabling statute itself (which the Court also ignores). The Maryland Act at issue has a section helpfully entitled “Purpose of collecting and testing DNA samples.” (One would expect such a section to play a somewhat larger role in the Court’s analysis of the Act’s purpose—which is to say, at least some role.) That provision lists five purposes for which DNA samples may be tested. By this point, it will not surprise the reader to learn that the Court’s imagined purpose is not among them.

So, to review: DNA testing does not even begin until after arraignment and bail decisions are already made. The samples sit in storage for months, and take weeks to test. When they are tested, they are checked against the Unsolved Crimes Collection—rather than the Convict and Arrestee Collection, which could be used to identify them. The Act forbids the Court’s purpose (identification), but prescribes as its purpose what our suspicionless-search cases forbid (“official investigation into a crime”). Against all of that, it is safe to say that if the Court’s identification theory is not wrong, there is no such thing as error.

I therefore dissent, and hope that today’s incursion upon the Fourth Amendment [] will some day be repudiated.

Notes, Comments, and Questions 

The dissent points out that the police did not really use the DNA to identify King; they used it to identify the source of sample obtained elsewhere; that is, they used the DNA test of King to match him to the pre-existing sample. In recent years, police have used DNA evidence to create profiles and search for family matches in ancestry DNA databases. What outcome under the Fourth Amendment?

Imagine a small community where two children are murdered.  Police believe they have a serial killer and obtain a confession for one of the murders from a local boy with developmental disabilities. DNA evidence proves the two victims had the same killer, but the evidence also exonerates the boy. The police want to obtain DNA samples from every male resident in the small town to find the murderer. What outcome under the Fourth Amendment? What if the police convince the entire male population to consent to giving DNA evidence; one man has a friend give DNA evidence on his behalf. Then later the friend comes forward to confess the subterfuge.  Analyze whether the police can require a DNA test from the man who sent the friend in his place. (Note: This question is based on a real case from England, in which Colin Pitchfork was eventually proven to have murdered two victims: Lynda Mann and Dawn Ashworth.) 


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