INTRODUCTION I. A PRIMER ON DNA FORENSICS A. Some Scientific Background B. Brief History C. Methods of Partial Matching II. EXISTING STATE POLICIES FOR REPORTING PARTIAL MATCHES A. Survey Methodology B. Survey Results--Policies Vary Widely 1. Distinguishing fortuitous and deliberate partial matches a. States permitting fortuitous but not deliberate partial matches b. States permitting both fortuitous and deliberate partial matches--but often imposing different restrictions for each c. States prohibiting deliberate partial matches, but not identifying a policy for fortuitous partial matches d. States prohibiting both fortuitous and deliberate partial matches 2. Unwritten policies 3. Additional requirements III. DISMANTLING THE DISTINCTION BETWEEN FORTUITOUS AND DELIBERATE PARTIAL MATCHING A. The Fortuitous/Deliberate Distinction Imposes Structural Costs 1. Perverse incentives for laboratory personnel 2. Perverse incentives for policymakers B. Arguments Favoring and Opposing Partial Matching Apply Broadly 1. Arguments favoring partial matching 2. Arguments opposing partial matching C. Arguments Favoring a Fortuitous/Deliberate Distinction Are Insufficient 1. "The key is intent" 2. Partial match quality 3. The direct costs of deliberate partial matching 4. The opportunity costs of partial matching 5. Institutional role 6. The near-perfect match CONCLUSION APPENDIX A APPENDIX B INTRODUCTION
On July 7, 2010, Los Angeles police announced that they had cracked a series of murders spanning decades, (1) arresting a suspect in the Grim Sleeper murders--so called because of an apparent hiatus in killings lasting a dozen years. (2) Although the serial killer had left DNA behind at several crime scenes, that DNA was not identical to any of several million DNA profiles of past offenders in the National DNA Index System. (3) The break in the case came when California searched its state DNA database for a genetic profile similar--but not identical--to the killer's. (4) Because DNA is inherited in specific and predictable ways, a partial match might indicate that a close genetic relative of the matching offender was the Grim Sleeper.
Partial matches may be uncovered in two ways: fortuitously or deliberately. Fortuitous partial matches are those discovered during routine database searches intended to identify exact matches. Deliberate partial matches are those uncovered through an intentional search of a DNA database for such matches. The intentional search for matches indicating possible familial involvement is frequently termed "familial searching." This Article adopts the terminology of "deliberate partial matching," however, to emphasize that the information uncovered by both fortuitous and deliberate means is functionally similar. Both draw investigative attention to offenders' kin who would not, absent their relation to a databased offender, be subject to genetic identification.
California first embraced partial matching in April 2008, when its Attorney General issued a well-publicized memorandum permitting the state lab not only to inform law enforcement investigators about partial matches fortuitously uncovered during routine database searches, but also to search deliberately for such matches. (5) The state developed special software for better identifying true familial relationships, (6) and set its sights on the Grim Sleeper as its first major target. (7) But initial efforts to identify a possible relative were unsuccessful. (8)
In April 2010, a new round of database searches produced several hundred partial matches--potential relatives, but likely more false leads. (9) To weed out these false starts, the state lab analyzed the Y chromosome of two hundred of the partial match results, comparing that data with the Y chromosome profile of the Grim Sleeper. (10) Because sons inherit their Y chromosomes from their fathers in full, fathers, sons, and patrilineal brothers all share the same profile. Of the two hundred potential relatives, one matched perfectly. (11) The police tailed the databased offender's father, Lonnie David Franklin, Jr. When Franklin threw out a slice of pizza, investigators nabbed it for testing. (12) Human DNA left on the pizza matched the Grim Sleeper DNA left at crime scenes. (13) To great fanfare, L.A. police arrested Franklin as the Grim Sleeper. (14)
The Grim Sleeper case highlights multiple controversies about the collection and use of DNA to crack cases. (15) First, California used a partial DNA match in its database to target a non-databased relative for investigation. Second, the state police obtained Franklin's DNA surreptitiously by collecting it from a discarded slice of pizza--no warrant required. Both of these issues pose thorny questions about what sort of privacy interest, if any, individuals can expect to have in their genetic information. Courts have routinely found that people have an expectation of privacy in their DNA. (16) But we shed DNA constantly, and as the Grim Sleeper case demonstrates, our relatives' DNA can be used to identify us.
This Article advances the conversation about partial matching--and about the use of DNA in criminal investigations more broadly--both by identifying the range and scope of state policies governing partial matches and by exposing the distinction that several states have drawn between fortuitous and deliberate partial matching as empty and dangerous. News reports about the Grim Sleeper explained that only California and Colorado have embraced deliberate searches for partial matches. (17) To be sure, in October 2009, Colorado announced that it would permit disclosure to investigators of both fortuitously and deliberately uncovered partial matches, and that it was employing specialized software to enable better familial identification. (18) But such reports do not come close to providing an accurate account of how states make use of partial matches in forensic investigation. In addition to California and Colorado, at least two other states presently permit both fortuitous and deliberate partial matching. (19) Only two jurisdictions, Maryland and the District of Columbia, have enacted statutes prohibiting deliberate partial match searches. (20) At least fourteen states, meanwhile, have permitted the investigative use of a fortuitously discovered partial DNA match, while simultaneously precluding, often explicitly, the deliberate search for such matches. (21)
This Article analyzes the distinction that these states have drawn between fortuitously and deliberately discovered partial matches, arguing that it imposes significant structural and transparency costs and yet is supported by neither logic nor principle. States should either permit both forms of partial match investigation, as California and Colorado have done, or permit neither.
This Article makes two distinct contributions to the growing literature on partial matching in forensic investigation. First, after Part I provides a primer on the science and history of forensic genetic identification, Part II sets forth a survey of state policies regarding partial matches. Reliable data about the range and scope of state policies governing partial matching have been hard to come by. This survey is the most complete dataset available on this issue.
Second, in Part III, this Article dismantles the distinction between fortuitous and deliberate partial matches and contends that states and the federal government cannot justifiably distinguish between them. The existing literature has thus far examined almost exclusively the more general question of whether the use of partial matches ought to be permissible at all. (22) None of this literature, however, has focused on actual state policies or on the wisdom of the distinction that so many states have drawn between fortuitous and deliberate matches. This Article does both, and so it is more immediately relevant to determining how states ought to address the ever-expanding scope of uses to which DNA databases may be put.
A PRIMER ON DNA FORENSICS
A basic understanding of the science and history of DNA matching is necessary for an informed exploration and critique of state policies governing partial matching. Subpart A describes the science of genetic identification. Subpart B then provides a brief overview of its history in the United States. Finally, Subpart C describes two methods by which partial matches may be uncovered during a database search--fortuitously or deliberately. Readers already familiar with these topics may wish to proceed directly to Part II.
Some Scientific Background
The average adult human body has between fifty trillion and one hundred trillion cells. (23) Nearly all of these cells have a nucleus that contains DNA, the genetic material that tells the cells how to reproduce, differentiate into different cell types, and grow. Each DNA sequence is comprised of a series of just four different bases: adenine (A), cytosine (C), guanine (G), or thymine (T). (24) In the ladder-like structure of DNA's double helix, each "rung" is a pair of bases matched in set patterns: As with Ts; Gs with Cs. (25) The sequence of these bases differs between individuals, encoding the information that makes each person, except identical twins, genetically different.
In humans, DNA is organized into twenty-three pairs of chromosomes. In each generation, different portions of the DNA sequence in the chromosomes from each parent are passed on to each child. (26) As a result, each child is unique, though she shares some parts of her sequence with her parents and also with her siblings, who likewise inherited parental DNA--but in a different mix. The total DNA sequence is what we mean when we refer to an individual's "genome." A human genome contains roughly 3.2 billion base pairs of DNA. (27)
Current research indicates that, although the genetic makeup of even unrelated individuals differs only by hundredths of a percent, (28) this still...