A familial DNA search is a search by law enforcement in DNA databases for genetic information indicating a relative of a person they seek to identify. When a search for an exact match to a DNA sample comes up fruitless, a search of familial DNA may bring back a partial match, indicating a sibling, child, parent or other blood relative. In fact, this is how the infamous Golden State Killer was finally identified and apprehended in 2018, more than 30 years after his last known crime spree.
For example, DNA from a crime scene might not match any DNA in state or federal databases, but if the person's son had been recently incarcerated and thus his information entered into a state DNA database, this type of search could lead police to the son, and ultimately to their suspect.
The following is an overview of familial DNA searches in criminal investigations.
Familial vs. Traditional DNA Search
Traditional DNA searches look for an exact match to a DNA sample. With a traditional DNA search, authorities can see whether crime scene DNA matches the DNA of anyone whose DNA has been collected in an array of state and federal DNA databases.
At this point, though they may differ in details, state and federal authorities collect DNA samples from the vast majority of convicted criminals. Federal authorities, along with a growing number of states and localities, also collect DNA samples from those arrested or charged with a crime.
A traditional DNA search bears fruit only if the DNA in question was already in one of the databases searched. Familial DNA searches allow authorities to expand such a search to effectively include relatives of those within searchable databases.
Gender and Familial DNA
Current forms of familial DNA searches work only with men. This is because techniques in common use to determine exact familial relations involve analysis of similarities on the Y chromosome (which is present only in males). Familial DNA searches as we know them today don't identify exact relatives of a female DNA sample, or female relatives of a male DNA sample.
While law enforcement may see familial DNA searches as a powerful new tool to track down suspected criminals, civil liberties advocates have criticized familial DNA searches as an invasion of privacy. They argue that familial DNA searching encroaches on the privacy of the relatives of those whose DNA has been collected through the penal system, in violation of the Fourth Amendment's protection against unreasonable searches.
Use by Law Enforcement
Currently, it's difficult to establish exactly which law enforcement agencies use familial DNA searches, since many states haven't formally adopted procedures to allow or ban them.
Only a limited number of states explicitly allow law enforcement officials to use familial DNA searches. Of these states, even fewer have issued public proclamations regarding familial searches. The policies in place in many states remain either unwritten or written in internal laboratory manuals.
At least one state, Maryland, has statutorily banned the use of this particular method.
The few states which have officially allowed familial searches vary widely on the conditions in which familial DNA searches may be preformed. For example, California officially allows familial DNA searches in investigations of major violent crimes in which the public faces safety risks and in which all other investigative avenues have proven fruitless.
Familial DNA Searches vs. Reporting Partial Results
There remains somewhat of a middle ground between traditional DNA searching and explicit familial DNA searching that involves partial matches that come up in a traditional DNA search. For example, a traditional DNA search, rather than an explicit search for family members, turns up a partial match. States vary in whether they allow such partial match information to be included in the results reported to law enforcement officials.
With written or unwritten policies, some states allow reporting of partial DNA matches, while others do not. Some states allow the reporting of partial match information but do not allow explicit searches for familial DNA. Places which allow partial match reporting might have a stated procedure in place setting out how and when to do so, or might make such decisions on a case by case basis.
Learn More About Familial DNA Searches by Speaking to an Attorney
Familial DNA searches are one way for investigators to discover new evidence in a case. If you're facing criminal charges based on a familial DNA search or if you object to providing DNA to authorities, you may want to contact a skilled criminal defense attorney who can advise you of your options and ensure that your rights are protected.