Familial DNA Searches

Forensic DNA from a crime scene sample might not match any DNA in state or federal databases. However, if law enforcement previously incarcerated the person's son, for example, officials likely entered the son's information in a DNA database. A DNA search, therefore, could lead police to the son and ultimately to their suspect.

Law enforcement often performs familial DNA searches when trying to identify an individual. They sometimes utilize DNA databases for genetic information to identify relatives of a suspect. If a search for an exact match to a DNA sample proves fruitless, a familial DNA search may bring back a partial match. A partial match may point to a sibling, parent, or other blood relative through DNA identification.

The following is an overview of familial DNA searches in criminal investigations.

What Is DNA Evidence?

DNA evidence is genetic evidence that law enforcement collects, typically from crime scenes. Every person has unique genetic material called genomes in their cells. A genome contains DNA unique to that individual. Forensic scientists can collect DNA from body tissues and cells, such as blood and hair. They can then conduct a DNA analysis in an attempt to identify crime suspects. This evidence allows law enforcement to compare DNA from a crime scene with a suspect's DNA.

Law enforcement has used DNA profiling to investigate crimes since Alec Jeffreys discovered the method in 1984. Law enforcement's use of DNA testing has expanded recently. This expansion is due to technological innovations and legislatures authorizing the technique's use.

Law enforcement's forensic science teams collect DNA samples from crime scenes. They then upload that data to a DNA databank, such as CODIS, which stands for Combined DNA Index System. The Federal Bureau of Investigation (FBI) designed CODIS. It allows law enforcement agencies across the United States to share DNA profiles. All 50 states, the District of Columbia, and the federal government use CODIS. Agencies take a specific DNA analysis from a crime scene sample and conduct a database search in CODIS. This may allow the agency to use the DNA profile from the collected evidence to identify a suspect.

DNA Evidence in the News

Agencies have used DNA testing to solve active and cold cases. In fact, this is how Joseph James DeAngelo, the infamous Golden State Killer, was finally identified and apprehended in 2018.

DeAngelo had eluded law enforcement for almost 40 years. Law enforcement then compared crime scene DNA from the 1980s to DNA held in a consumer database. They then spent months constructing the Golden State Killer's family tree. They eventually identified DeAngelo's great-great-great-grandparents, which ultimately led them to DeAngelo himself.

More recently, law enforcement used DNA testing to identify Bryan Kohberger, the man accused of killing four college students in Idaho in November 2022. A tip pointed FBI investigators toward Kohberger. They compared a DNA sample taken from trash at his home to unknown DNA from a knife sheath left at the crime scene. Tests revealed that the sample taken from the home likely belonged to the biological father of the person whose DNA was on the knife.

Later DNA tests revealed a direct link to Kohberger. Investigators claim that the DNA found on the sheath was “at least 5.37 octillion times more likely to be Kohberger's than an unrelated member of the public," according to NBC News.

Traditional vs. Familial 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 any DNA in a DNA database.

State and federal authorities collect DNA samples from most convicted criminals. Law enforcement entities also often collect samples from suspects 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 testing and searches allow authorities to expand the net. Familial testing lets law enforcement identify relatives of an unknown suspect. Therefore, if an unknown suspect's family member is a convicted offender, familial DNA testing may help authorities identify the suspect.

Familial DNA Searches vs. Reporting Partial Results

A middle ground exists between traditional DNA searching and explicit familial DNA searching. A traditional DNA search may turn up a partial match. States vary as to whether law enforcement can include this partial match information in their reports.

Partial matching involves searching within CODIS to identify potential family relationships. The search looks for a relationship between a known DNA sample and an unknown individual whose DNA was previously collected. Technically, it involves determining whether the DNA samples share genetic material at a specific location on a chromosome, known as a genetic locus.

Law enforcement may use information gathered from a partial match in an investigation. Whether law enforcement will use the data, though, depends on the state's laws.

Some states allow reporting of partial DNA matches, while others do not. Other states allow the reporting of partial match information but do not allow explicit searches for familial DNA. Some states that allow partial match reporting have a stated procedure. Other states might make such decisions on a case-by-case basis.

Gender and Familial DNA

Some forms of familial DNA searches tend to work only with male suspects or relatives. The Y-STR analysis technique compares genetic information found only on Y chromosomes. The Y chromosome is usually only present in male DNA.

Mitochondrial DNA testing, which some law enforcement agencies use in missing-persons cases, instead helps to find genetic matches through maternal lines. But mtDNA analysis has seen less use in criminal applications than Y-STR analysis.

The FBI Laboratory says it can conduct both Y-STR and mtDNA analyses, along with other forms of DNA testing. Forensic science is an ever-evolving field, and these methods don't offer 100% conclusive results. The Global Justice Information Sharing Initiative cautions that using DNA databases to look for suspects' relatives "can potentially provide an investigative lead (as opposed to exact identification) that may ultimately help identify the perpetrator of a serious crime."


Civil liberties advocates have criticized law enforcement's use of familial DNA. They argue that familial DNA searching infringes on citizens' privacy interests. They say that family members of convicted offenders should not be subject to a diminished level of privacy. They also argue that such searches violate family members' Fourth Amendment protections.

Many also note that people of color are overrepresented in DNA databanks. Critics, such as the Legal Aid Society in New York City, argue that this leads to a disparate impact of familial DNA searches on minorities. The Legal Aid Society sued New York State in 2018 after the state expanded the use of DNA databanks. The group argued that the Division of Criminal Justice Services and the Commission on Forensic Science acted beyond their authority by expanding the use of such databanks.

Additionally, critics argue that further expanding DNA collection raises ethical concerns. They do not want the collection to extend beyond convicted offenders. For example, they reject the use of victims' DNA in law enforcement databases. The city of San Francisco faced a federal lawsuit in 2022 after DNA from a sexual assault case led to a victim's arrest in an unrelated burglary. A California law that took effect in 2023 now bars that practice.

Supporters of familial DNA searches see it as a powerful tool for criminal investigations. Specifically, proponents say it helps law enforcement identify and convict suspects. Forensic teams often share their findings with local law enforcement or the district attorney's office. They say it also helps them develop investigative leads and resolve cold cases. Additionally, they point to familial DNA searches that have exonerated wrongfully convicted people. Finally, they argue that these searches improve public safety.

As the federal Office of Justice Programs (OJP) noted, familial DNA searches are still relatively new in the United States. The impact of these searches will only be understood as more states adopt them. As law enforcement continues to conduct these searches, litigation will surely arise. A criminal defense attorney can provide you with the latest legal advice regarding familial DNA searches.

Law Enforcement's Use of Familial DNA Searches

Many states have not formally adopted procedures on familial DNA searches. Only a few states explicitly allow law enforcement officials to use familial DNA searches. Of those states, even fewer have issued public proclamations regarding familial searches. As noted by the OJP, most states leave the decision to agencies rather than their legislatures.

In May 2022, however, a New York court curbed state law enforcement's ability to use familial DNA searches. New York's Division of Criminal Justice Services had adopted regulations on the searches in 2017. The appellate court ruled that the regulations were invalid. The court noted that the New York State Legislature did not consent to the state Commission on Forensic Science's search regulations. The court wrote that these issues present policy questions that the legislature should decide.

The few states that allow familial searches vary on the conditions that allow law enforcement to perform the searches. For example, California has allowed familial DNA searches, but only in certain investigations. The state has said it permits searches in major violent crimes where the public faces safety risks. They are also only allowed after all other investigative avenues have proven fruitless. Colorado was the first state to allow familial DNA searches.

Consumer DNA Databases

In 2021, Maryland and Montana passed laws regarding consumer DNA databases. They now require law enforcement to obtain judicial authorization before searching consumer databases in criminal investigations. Consumer DNA databases contain millions of people's DNA data. People use these databases, including 23andMe and Ancestry.com, to learn more about their family tree.

The wealth of data in these databases also appeals to law enforcement. In theory, law enforcement agencies could use these databases for many purposes. If they have a suspected offender's DNA, they could compare it to the millions of consumers who have used the services. That would allow law enforcement to narrow down familial DNA testing and searches.

Again, this raises Fourth Amendment concerns about consumers' right to privacy. The Fourth Amendment requires law enforcement to show probable cause before a valid search is conducted. Critics of the approach argue that law enforcement does not have probable cause to search a person's DNA when they have no connection to a crime.

Learn More About Familial DNA Searches by Speaking to an Attorney

Criminal law is complex. Familial DNA searches are one way for investigators to discover new evidence in a case. You should contact a skilled criminal defense attorney if you face criminal charges based on a familial DNA search. An attorney can advise you of your options and protect your rights.

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