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Constitution Check: What are the limits on police testing of DNA?

June 4, 2013 by Lyle Denniston


dnaLyle Denniston looks at the unanswered questions from the Supreme Court’s ruling on DNA swabbing of criminal suspects, including limits on what the police can do and which people can see the results.


“If in the future, police analyze [DNA] samples to determine, for instance, an arrestee’s predisposition for a particular disease or other hereditary factors not relevant to identity, that case would present additional privacy concerns not present here.”

– Justice Anthony M. Kennedy, writing for the Supreme Court majority in the 5-4 decision on Monday in the case of Maryland v. King, upholding the constitutionality of mandatory sampling by police of the DNA of every individual arrested for a serious crime


Each time the Supreme Court takes a new step in an area of constitutional controversy, it rules on the specific case before it, but very often leaves a list of unanswered questions in the wake of that decision. Case by case in recent years, the court has been working out the constitutional rules that will govern how police, prosecutors, and crime labs deal with the new wave of technology known as DNA analysis.

That is the process of determining an individual’s genetic profile by examining the makeup of that person’s body chemistry: the composition of basic human cells. Obviously, it has uses outside the field of crime investigation, because such analysis can determine, for example, whether a woman is susceptible to certain forms of breast and ovarian cancer. Hollywood actress Angelina Jolie recently learned from such a test that she was prone to cancer, and thus underwent a double mastectomy to reduce her risk.

In law enforcement, DNA testing has proven to be fantastically accurate in identifying suspects who committed crimes, and thus in solving “cold cases.” But it also has cleared scores, perhaps hundreds, of individuals who got caught up in a criminal investigation but did not actually commit the offense.

The government, though, does not have unlimited authority to test DNA, because sampling DNA is now understood to be a search, and thus potentially restricted by the Fourth Amendment’s ban on “unreasonable” government searches. The Supreme Court’s task has been to sort out what is “reasonable” in DNA testing. That is the task that it took on anew in the case of Maryland v. King, involving potentially the constitutionality of the laws of the federal government and of 29 state governments. Although only Maryland’s specific law was directly at issue, it is clear that the court was making a decision that would likely apply to all similar laws—and, very likely, given the outcome, encouraging other states to join in enacting such laws.

Nine years ago, Maryland’s state courts had ruled that there was no Fourth Amendment problem when police took a DNA sample, without a warrant, from every individual who actually had been convicted of a serious crime. Such individuals already had forfeited a lot of their right to privacy, and sampling their DNA was only a slight further intrusion, according to that ruling.

The state’s highest court, however, last year balked at police DNA sampling of every individual who had been arrested for a serious crime—that is, well before they actually had been convicted of any crime. That went too far, and violated the Fourth Amendment right of privacy, the state court ruled in the case of Alonzo Jay King Jr. He had been tested after his arrest on an assault charge—in a case totally unrelated to any “cold case” unsolved in Maryland. His DNA sample, however, matched evidence found at the scene of an unsolved rape that had occurred years before. He was put on trial for the rape, was convicted, and was sentenced to life in prison without parole.

The Supreme Court’s five-justice majority ruled Monday that King’s Fourth Amendment rights were not violated. Learning the identity of an individual at the time of his arrest for a “serious” crime, the majority said, has long been routine police practice, and finding out whether an individual had a criminal record was a normal part of that practice. DNA testing, Justice Anthony M. Kennedy wrote, is not that much different from taking fingerprints or photographs during booking, except that it is better at identification.

Criminal suspects, the majority said, may go to some lengths to try to conceal their looks, or even their fingerprints, but they can’t fool their DNA profile.

At first glance, that appears to validate the laws of more than half of the states and of the federal government. But what remains uncertain about the scope of that ruling? Here are some of the questions that can only be resolved when the court returns to the issue in future cases:

If police authority to take an involuntary DNA sample exists only for those arrested for “serious” crimes, what crimes qualify? The decision did not say.

What did the court say about the constitutionality of extending such sampling to people arrested for minor crimes, such as jaywalking or shoplifting? The dissenting opinion said the court had not ruled that out, and the majority opinion did not attempt to answer that argument.

What restrictions must a state, or the federal government, put on how a DNA sample may be used in order for the procedure to be valid under the Fourth Amendment? The court found a number of safeguards in the Maryland law, such as limiting use solely to identifying an individual, but it did not say those were constitutionally necessary elsewhere. The court hinted that looking into an individual’s medical or family profile might be problematic constitutionally.

Who is to be given access to the results of DNA sampling? Potential employers? Other government agencies weighing eligibility for public programs? The court imposed no specific limits on sample-sharing, thus making that depend upon what a legislature is willing to do.

The ruling, of course, was a major victory for law enforcement. But it left enough doubt as to ensure that the issue will come back again.

Lyle Denniston is the National Constitution Center’s adviser on constitutional literacy. He has reported on the Supreme Court for 55 years, currently covering it for SCOTUSblog, an online clearinghouse of information about the Supreme Court’s work.

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