by David H. Kaye

Distinguished Professor and Weiss Family Scholar
Dickinson School of Law
Graduate Program in Forensic Science
The Pennsylvania State University

Twenty-five years ago, DNA databases were a curiosity thought to be useful only for a few types of violent crimes.[1] Today, they are a dazzling device for enforcing criminal laws from car theft to murder.[2] Computer trawls of DNA databases for matches to DNA profiles from crime-scenes or from the bodies or clothing of victims have produced hundreds of thousands of “cold hits” to known offenders.[3]

These routine trawls are “inner-directed” in that their targets are confined to the men and women represented in the database. However, less common “outer-directed” trawls, known colloquially as “familial searching,” have produced some spectacular successes. In the U.S., the most famous is the trawl of California’s database in April 2010 that seems to have unmasked a serial killer operating for some 25 years. This database search generated a suspicious partial match to “a young man named Christopher Franklin convicted . . . on a felony weapons charge.”[4] The pattern of matching and nonmatching DNA alleles was many times more probable if “the Grim Sleeper” killer was the father of the young Franklin than if the killer was not paternally related. The police then placed the father, Lonnie Franklin, under surveillance and surreptitiously acquired his DNA from a discarded slice of pizza at a restaurant. When that DNA sample matched samples from the Grim Sleeper’s victims, police arrested him.[5]

Despite such highly publicized successes, outer-directed trawling has been pilloried as a step “towards eugenics and corruption of blood,”[6] “biological determinism,”[7] “mission creep,”[8] “a major privacy intrusion in the life of families,”[9] “guilt by association,”[10] “genetic surveillance for all,”[11] and “lifelong genetic surveillance”[12]that is “inconsistent with a basic pillar of American political thought.”[13] This essay analyzes three constitutional claims about the emerging practice of outer-directed trawling that infuse such rhetoric—that it is an infringement of constitutionally protected familial privacy, an affront to the presumption of innocence, and an unconstitutional “corruption of blood.” Upon inspection, the relevant constitutional provisions lend no more than metaphorical support to these objections to “familial searching.”


One perceptive commentator has proposed the argument that familial searching “does implicate the fundamental right to liberty and free association, or even some notion of a fundamental right to familial privacy, in which case the practice would receive heightened scrutiny.”[14] While not fully endorsing this argument, Professor Erin Murphy observed that “[t]he Court has also previously recognized that harms can flow from the forced disclosure of associational ties, even outside of the genetic context, and has been particularly protective of the familial bond.”[15] The relevant cases, however, are far removed from outer-directed trawling. Cases on “the forced disclosure of associational ties” deal with the different value of “preserving political and cultural diversity and shielding dissident expression from suppression by the majority.”[16] In National Ass'n for Advancement of Colored People v. State of Alabama ex rel. Patterson,[17] for example, the Court held that the state could not require the NAACP to produce the names and addresses of all members and agents. The “freedom to engage in association for the advancement of beliefs and ideas”[18] is central to the First Amendment, but it has next to nothing to do with using traces of DNA to locate the perpetrators of crimes. Locating suspects through the acts and DNA of their relatives, whether just or unjust, is not an attack on “political and cultural diversity.”

A separate line of cases, noted in Roberts v. U.S. Jaycees,[19] does protect “freedom of intimate association”[20]in order to “afford the formation and preservation of certain kinds of highly personal relationships a substantial measure of sanctuary from unjustified interference by the State.”[21] In Roberts itself, the Court rejected a claim that this “freedom of intimate association” extended to decisions about who can join a “large and basically unselective”[22] civic association. In particular, associational privacy was no obstacle to a state civil rights law that prevented the Jaycees from limiting full membership to men between the ages of 18 and 35. 

Neither this result nor the reasoning in Roberts reveals much about a possible right of an individual to be free from criminal investigations resulting from the conduct of another family member.  Justice Brennan’s opinion for the Court cited Pierce v. Society of Sisters[23] and Meyer v. Nebraska[24] as establishing the “substantial measure of sanctuary.”[25] Pierce and Meyer applied stricter-than-normal scrutiny to laws demanding that parents enroll their children in public rather than private schools (Pierce) and forbidding schools from teaching any foreign language before the ninth grade (Meyer). In Paul v. Davis,[26] the Court explained that the “intimate association” decisions deal with “matters relating to marriage, procreation, contraception, family relationships, and child rearing and education.”[27] Locating the possible sources of DNA deposited in the course of violent or other crimes by inspecting profiles legitimately taken from convicted offenders lies light-years away from the cases on substantive due process “privacy” rights or general notions of liberty and intimacy in family settings.[28]


A second and more common refrain in the debate on outer-directed DNA database trawls is that placing family members at risk for coming to the attention of the police “diminishes the presumption of innocence.”[29]However, the “presumption” should not—and never has—protected individuals from becoming persons of interest, prime suspects, or even full-fledged defendants because of the actions of their relatives. If Esau is interrogated because police think he knows something about his brother, Jacob, and Esau unwittingly supplies information that helps police build a case against Jacob, Jacob can hardly raise the presumption that he is innocent until proven guilty as a bar to the legitimate acquisition of evidence of guilt.

The situation does not change just because the inadvertently supplied information is genetic. Suppose that Esau but not Jacob has a criminal record. A convenience store was robbed, and the store clerk picked Esau’s photograph out of a photo spread. However, the robber dropped a tissue on the floor as he fled from the store. The crime laboratory recovered DNA from the tissue and excluded Esau as the source because there were mismatches at several DNA loci. A laboratory analyst thinks that the fact that the samples almost match is indicative of siblingship. An enterprising detective checks with the state’s Office of Vital Statistics and learns that a younger Jacob has the same parents as Esau. The detective secures an order for Jacob’s DNA. The DNA matches at every allele of every locus, and Jacob is charged with the robbery. Again, Jacob’s invocation of the presumption of innocence would be frivolous.

Finally, suppose that Esau was located not through the store clerk’s memory, but from a search of the convicted offender database for full matches—there were none—and near misses—there was one, to Esau. The magistrate grants an order for Jacob’s DNA on the strength of the inference of siblingship and a police investigation that showed Jacob’s credit card was used just before the robbery at a gas station three blocks from the convenience store. Jacob resists on the ground that the police investigation violated the presumption that he was innocent.

Jacob’s objection would be pointless because historically and at its core, the presumption of innocence is an aspect of the right to due process of law that applies at trial rather than during investigations.  The “presumption” prevents the mere fact that government authorities have charged an individual with a crime to be treated as evidence of guilt.[30] The Supreme Court confirmed this in Bell v. Wolfish,[31] when it explained that the presumption of innocence “has no application to the determination of the rights of a pretrial detainee during confinement before his trial has ever begun.”[32] Likewise, both the Universal Declaration of Human Rights and the International Covenant on Civil and Political Rights explicitly limit the presumption to individuals “charged with” crimes.[33]

Other provisions in these documents and in the U.S. Constitution protect against arbitrary or discriminatory arrests and searches, and that is where the constitutional objections to “familial searching” should dwell.[34]Although it is possible to use the phrase “presumption of innocence” loosely in public discourse or metaphorically in legal arguments, this principle gives no additional constitutional oomph to the demands of due process and equal protection in criminal investigations or to the protections from unreasonable searches and seizures.


A final constitutionally based phrase—“corruption of blood”— infuses the harshest criticism of kinship matching.[35] In an early and thoughtful article, Professor Hank Greely and his colleagues introduced the phrase into the debate—and promptly dismissed it.[36] As they explained:

Corruption of blood, which the colonies inherited from English common law, stripped the descendants of anyone convicted of a felony of their right to inherit the felon's estate, any noble title, or any other “hereditament.” The Constitution itself prohibits “corruption of blood,” at least for one crime, stating “The Congress shall have Power to declare the Punishment of Treason, but no Attainder of Treason shall work Corruption of Blood, or Forfeiture except during the Life of the Person attainted.”[37]

In view of the limited scope and purpose of the Clause, no one can plausibly contend that the prohibition on corruption of blood means that police cannot use information acquired as a result of knowing who is in a family or that they cannot treat family membership as a relevant consideration in their investigations.[38] The government should not punish children for the sins of their fathers, but this precept does not shelter the physical similarities of the fathers from discovery.[39]

* * *

In sum, constitutional “privacy,” the “presumption of innocence,” and “corruption of blood” are hollow objections to outer-directed trawling. The government should not punish the child for the sins of the father. The government should not dictate what parents can teach their children. The government should not brand and punish individuals as criminals without due process of law. But discovering evidence through genetic proximity is far removed from corruption of blood, interference with fundamental family decisionmaking, or withdrawing the presumption of innocence. Guilt by association is reprehensible, but association can lead to evidence of guilt. If there is a constitutional infirmity in acquiring this evidence from the DNA of relatives, it is the product of other constitutional constraints.