Families and Forensic DNA Profiles

Law enforcement officials often turn to DNA identification methods to detect—and rule out—possible offenders. Every state operates its own database of convicted offenders' DNA profiles; some states store profiles of arrested people, too. The Federal Bureau of Investigation maintains a national database of profiles submitted by laboratories across the country.

A few years ago, officials came up with a new way to use DNA profiles in forensic identification. Ordinary searches require an exact match between DNA found at a crime scene and a forensic DNA profile. A partial match means that the profiled individual should not be considered a suspect. But partial matches create another possibility: the crime scene DNA may come from a relative of the individual whose profile is in the database.

The United Kingdom has used partial matches to identify unknown offenders in several high-profile cases, and the technique is gaining traction in the United States. The 2010 identification of a suspected serial killer could accelerate this trend.

The "Grim Sleeper"

Last summer, a familial DNA search led police to a man believed to have killed at least ten women in the Los Angeles area. The killings occurred between 1985 and 2007. (Initially, police thought the killer had been inactive for part of that time, and this gave rise to the "Grim Sleeper" epithet.) Prosecutors have charged Lonnie David Franklin, Jr., with the murders.

Before the familial search, efforts to trace DNA found at the crime scenes had been unsuccessful. Franklin's DNA profile was not in the forensic database. Although he had previously been convicted of possessing stolen property, his convictions occurred before California started collecting DNA from people who had committed that offense.

The familial DNA search found a partial match between DNA recovered from the victim's bodies and DNA from an offender whose profile was in the forensic database. The police put together a list of that offender's male relatives, focusing on the ones who lived nearby and were old enough to have committed the murders. This led them to the offender's father, Lonnie David Franklin, Jr. They began tracking Franklin's movements and eventually were able to retrieve his discarded food and utensils from a restaurant. The DNA on those items matched DNA samples from the murder scenes.¹

California is one of a relatively small group of states with a published policy on partial DNA matches. A 2008 directive from the state attorney general's office authorizes forensic laboratories to report partial matches to police and to conduct DNA searches specifically aimed at identifying an unknown perpetrator's relatives.² Maryland has gone in the other direction, enacting a law that prohibits familial DNA searches. Many states lack clear rules on these practices; in others, officials have adopted internal laboratory rules without public disclosure and debate. The FBI's current policy gives states authority over whether to permit partial match searching and reporting.³

Benefits and Harms

Franklin's arrest dramatically illustrates the benefits that familial DNA identification can produce. If his guilt is established, California's familial search will have removed a dangerous killer from the streets and enabled society to punish that killer. Besides helping law enforcement officials apprehend more criminals, familial identification could deter others from future criminal activity. And familial DNA identification could protect innocent people from wrongful arrest and conviction.⁴

On the other side of the equation are the potential harms produced by familial identification. The approach raises several family privacy concerns. The genetic information recorded in forensic databases consists of short DNA stretches with no known role in determining a person's disease susceptibility or behavioral characteristics. But the actual biological samples taken from crime scenes, suspects, and relatives contain much more DNA. Few states explicitly prohibit sample analysis that could reveal information about a person's genetic traits and predispositions. Familial searches can also uncover mistaken beliefs about biological relatedness. Because many states lack clear rules addressing these matters, there is a possibility that law enforcement officials will improperly discover, and disclose, important personal information about families.

Other types of intrusions are likely as well. Police officers pursuing genetic leads...