Chapter 14, Problem 3CS

Can DNA profiling identify the source of a sample with absolute certainty? Because any two human genomes differ at about 3 million sites, no two persons (except identical twins) have the same DNA sequence. Unique identification with DNA profiling is therefore possible if enough sites of variation are examined. However, the systems used today examine only a few sites of variation. Nonetheless, even with today’s technology, which uses three to five loci, a match between two DNA patterns can be considered strong evidence that the two samples came from the same source.

DNA profiling in criminal cases has been a useful tool in establishing both guilt and innocence. Originally, DNA databases contained only the profiles of convicted felons. Over time, however, law enforcement agencies have expanded the collection and use of DNA profiles, and these new policies are causing controversies, once again illustrating how the availability and use of genetic technology is often ahead of consensus on how and when this technology should be used. One of these new policies is postarrest DNA collection.

At this writing, 18 U.S. states as well as the federal government allow the collection of DNA samples after an arrest but before conviction. These profiles become part of the state’s DNA database, which is often searched for evidence in cold cases. Courts across the country have ruled for and against the use of such samples.

In 2012, the Maryland Court of Appeals ruled that the collection of DNA samples from someone who has been arrested but not convicted is unconstitutional and violates an individual’s right to be free from unreasonable search and seizure. The case began when a DNA sample was taken from Alonzo Jay King, Jr., who was arrested in 2009 for assault. In a database search, the DNA profile matched that taken from a 2003 unsolved rape. Based on the results of the database search, the man was sentenced to life in prison. The rape conviction was reversed, and the case was sent back to a lower court. As a result, some 16,000 DNA profiles collected postarrest but preconviction since 2009 cannot be used pending appeal of this decision. Before the court decision, postarrest DNA profiles were used in 65 arrests that resulted in 34 convictions, with an additional 12 cases pending.

Supporters of postarrest DNA profiling claim that taking a DNA sample by a cheek swab is noninvasive and no different from taking someone’s fingerprints. Opponents claim that because DNA samples can be used to determine much more than a DNA profile, they are a threat to privacy, and that because minorities are more likely to be arrested, the practice is discriminatory.

What if you learned that law enforcement officials were saving the DNA sample for use in tests that might be developed in the future?