Supreme Court Allows DNA Collection After an Arrest


dnaThis week the Supreme Court decided that it is not a violation of the 4th Amendment for law enforcement to take a DNA sample from people who are arrested. The Court said that a cheek swab was no different than mug shots or fingerprinting; its purpose is to identify the person in custody. From the New York Times:

The police may take DNA samples from people arrested in connection with serious crimes, the Supreme Court ruled on Monday in a 5-to-4 decision.

The federal government and 28 states authorize the practice, and law enforcement officials say it is a valuable tool for investigating unsolved crimes. But the court said the testing was justified by a different reason: to identify the suspect in custody.

“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,” Justice Anthony M. Kennedy wrote for the majority, “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 was deeply divided with four of the justices realizing that these DNA samples were for more than just identification. They were a fishing expedition for suspects in cold cases. Scalia wrote the dissent:

Justice Antonin Scalia summarized his dissent from the bench, a rare move signaling deep disagreement. He accused the majority of an unsuccessful sleight of hand, one that “taxes the credulity of the credulous.” The point of DNA testing as it is actually practiced, he said, is to solve cold cases, not to identify the suspect in custody.

But the Fourth Amendment forbids searches without reasonable suspicion to gather evidence about an unrelated crime, he said, a point the majority did not dispute. “Make no mistake about it: because of today’s decision, your DNA can be taken and entered into a national database if you are ever arrested, rightly or wrongly, and for whatever reason,” Justice Scalia said from the bench.

You may ask why this was even an issue since people who get arrested must be bad people right? Not necessarily. Do not equate being arrested with being convicted of a crime. For those convicted, taking a DNA sample is more than appropriate and an important tool for solving unsolved crimes.  But just being arrested is wholly another thing. Many people are arrested for crimes they did not commit.

This was a bad decision for many reasons. First, Scalia is right. A DNA sample goes way beyond simple identification. That sample has information in it that the government does not have any business knowing about unless you are actually convicted of a crime. Try getting paternity, health or “criminal gene” information from a mug shot or fingerprinting.

Second, this overloads an already overloaded system. As this Washington Post piece points out:

A Department of Justice study estimated that around 900,000 requests for biological screening, mostly DNA testing, were backlogged nationally at the end of 2009, the most recent year for which data is available. Meanwhile, large numbers of kits from routine arrests may be making the problem worse, argued Brandon Garrett, a professor at University of Virginia School of Law.

“As taking more DNA from arrestees has increased, the backlogs have increased at the expense of testing DNA from actual crime scenes,” he said.

Garrett also said that simply adding a DNA sample from everyone who is arrested might even make it harder for police to identify criminals, increasing the likelihood of false positives without adding any perpetrators to the system.

“A lot of innocent people will have their DNA in these databases,” he said. “That dilutes the databases and weakens their power.”

Garrett is right. Forensic DNA testing looks at short sequences that are repeated over and over. These repeated regions are called short tandem repeats or STRs. The places where these STRs occur are called loci. There are many variations in the lengths of STRs (I may have 5 repeats at a particular loci and you may have 8 ) and by looking at many different loci scientists create a kind of profile or human bar code that is unique to each individual. This technique is also used to determine parentage because you inherit half of your unique barcode from your mother and half from your father.

After scientists analyze the DNA found at a crime scene, they compare it to the suspect’s DNA to see if their barcodes match. The more loci where the STRs match, the more likely that the DNA comes from the same individual. Typically, to make sure that the barcodes matched, labs in the United States look at 13 loci. Labs in the United Kingdom look at 10 loci.  If all 10-13 loci had the same lengths of STRs, it was said that the DNA was from the same individual. The lower the number of loci, the less confidence the DNA is a match. In other words the longer the barcode, the better the identification tool.

The problem comes from the fact that most DNA from a crime scene is not perfect.  It can be degraded or mixed with DNA from other individuals.  Sometimes labs can only match 9 loci to the DNA found at a crime scene.

Scientists are starting to question this assumption that 10-13 loci are enough to rule out the possibility of a random match to DNA other than the suspect. In other words, if 10-13 loci are not enough to make a definitive barcode, then a 10-13 loci DNA profile can actually match more than one individual. According New Scientist, a recent look into the possibility of random matches produced some serious results:

The first clue that something might be amiss came in 2005, when limited data was released from the Arizona state database, a small part of CODIS. An analyst who compared every profile with every other profile in the database found that, of 65,493 profiles, 122 pairs of profiles matched at nine out of 13 loci and 20 pairs matched at 10 loci, while one pair matched at 11 loci and one more pair matched at 12 loci. “It surprised a lot of people,” says signatory Bill Thompson of UCI. “It had been common for experts to testify that a nine-locus match is tantamount to a unique identification.”

So in a sample of 65,000 profiles, 122 profiles matched at 9 loci, 20 profiles matched at 10 loci, and 1 profile matched at both 11 and 12 loci.  According to Bill Thompson, experts have testified that 9 loci is enough for a unique profile. This comparison calls into question the assumption that 9-13 loci are enough to definitively match a suspect’s DNA to that found at a crime scene.

The more people law enforcement adds to this database, the more likely a false positive will result. Taking the DNA of arrestees does indeed “dilute the databases and weakens their power.”

This ruling also makes the assumption that if you are innocent when arrested you have nothing to worry about. It assumes that forensic labs never make mistakes or never perpetrate fraud. Unfortunately that is not the case. Just last year a scientist in the Department of Public Health Lab in Massachusetts admitted to falsifying data in thousands of cases. The Scientist reported:

The results from roughly 34,000 criminal drug cases were put into question earlier this year, when forensic chemist Annie Dookhan at the shuttered Department of Public Health Lab in Massachusetts was discovered to have falsified records on samples she was assigned to process. Instead, she forged signatures and did not perform tests she recorded as complete, according to investigations.  Suspicions may have first arisen due to her impressive output—she claimed to have processed 9,000 samples in a year, whereas colleagues only averaged around 3,000. As a result of her actions, a number of defendants may have been wrongly imprisoned, while others who may have been rightly accused were freed.

Scientists are people too. We make mistakes and sometimes we commit fraud to further our careers. The power of DNA testing for forensics should be limited. DNA databases should consist of samples from those convicted of crimes not clogged with samples from anyone who has ever been arrested. The chances for misuse are just too great. Besides the 4th Amendment is supposed to protect us from “unreasonable searches and seizures.” I think taking DNA from those not yet convicted of a crime qualifies.


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