DNA technology plays a significant role in the criminal justice system. DNA evidence is an extremely powerful tool for identifying and convicting perpetrators—including in so-called "cold cases" where DNA evidence can solve crimes years after they were committed. DNA evidence can also exonerate innocent people who were wrongly convicted. The Innocence Project, for example, has used DNA evidence to help free or exonerate more than 200 people.
But what are the rules for collecting and storing DNA for law enforcement purposes? There's no single answer to that question, because each state (as well as the federal government) makes its own laws covering when DNA can be collected from someone who's been arrested, charged, or convicted of a crime. But some rules are either universal, or followed by a majority of jurisdictions. For example, the federal government and all of the states allow DNA collection when someone is convicted of a crime. And the Supreme Court has ruled that it's constitutional for the police to collect a DNA sample from someone who's been arrested for a serious offense.
This article discusses the basics of post-conviction and pre-conviction DNA collection laws, including which crimes qualify for sample collection, when the sample is taken and where it’s stored, whether juveniles are required to provide a sample, and the process of expunging a sample.
Post-Conviction DNA Collection Laws
All states authorize DNA collection from individuals who have been convicted of certain crimes. And, under federal law, the “DNA Analysis Backlog Elimination Act” requires police to collect DNA from defendants convicted of a qualifying federal crime.
Qualifying crimes. DNA is collected only for convictions of qualifying crimes. Jurisdictions vary in defining which crimes qualify. Some jurisdictions require offenders to provide a DNA sample for any felony conviction. In other jurisdictions, DNA is collected from people who are convicted of specific crimes, such as violent crimes, burglary, or sex crimes.
When DNA is collected. All jurisdictions require offenders to provide a DNA sample after a conviction of a qualifying crime. Under some laws, the state collects DNA even if the defendant is found not guilty by reason of insanity. In a few states, individuals on parole or probation are required to provide DNA samples as a condition of release.
Juvenile cases. Post-conviction DNA collection applies to juveniles in some jurisdictions. However, some states require juveniles to provide a DNA sample only for conviction of a crime that would be a felony if committed by an adult. Other states explicitly exempt juveniles from providing DNA samples, regardless of the crime classification.
Can the Police Collect DNA After an Arrest?
A person doesn't always have to be convicted before they can be required to provide a DNA sample. In the 2013 case Maryland v. King, the Supreme Court ruled that DNA samples can be collected from people who are arrested for certain "serious" offenses. The majority in that case ruled that taking a cheek swab to collect an arrestee's DNA did not violate the Constitution's Fourth Amendment. The Court reasoned that arrestees have a lower expectation of privacy than non-arrestees, and that collecting a buccal swab was a "minor intrusion"—similar to taking an arrestee's photograph and fingerprints. It therefore decided that the benefits to law enforcement outweighed a suspect's rights to privacy and to be free from unreasonable searches. (Maryland v. King, 569 U.S. 435 (2013).)
Four of the nine justices disagreed with the outcome of Maryland v. King. The dissenting justices said that taking an arrestee's DNA sample was a search under the Fourth Amendment, and that the search had to be supported by probable cause. Under the Constitution, a person cannot be arrested unless there's probable cause to believe they committed the crime they were arrested for. But the dissent pointed out that probable cause to arrest someone for a specific crime does not automatically create probable cause to search for evidence of any crime. For example, if someone is pulled over and arrested for reckless driving, it doesn't automatically mean there's probable cause to search that person's home for evidence of unrelated crimes. And this, according to the dissent's logic, is essentially what the police are doing when they collect a DNA sample from an arrestee and then try to match it to any of the millions of DNA samples collected from crime scenes and stored in government databases.
While the dissent raised important questions about DNA collection, the majority's ruling in Maryland v. King remains the law of the land. More than two-thirds of states have laws authorizing the police to obtain DNA from a person who has been arrested or charged with certain crimes. Federal law also authorizes DNA collection from people in federal custody, even if they have not been convicted. The procedures and requirements for collecting DNA from arrestees vary by jurisdiction.
Qualifying arrests. In states that authorize pre-conviction DNA collection, arrestees are required to provide a DNA sample only for arrests of certain crimes. The more serious the crime, the more likely it is that a DNA sample will be required. Some states authorize DNA collection for all felony arrests, while others limit collection to certain specified felonies—for example, burglary, sex crimes, or crimes involving violence. A few states also allow DNA collection for certain misdemeanor arrests, or use an arrestee's prior criminal record to decide if a sample will be taken.
When DNA is collected. Generally, an arrestee is required to provide a DNA sample during the booking procedure, following the arrest. However, a few states authorize DNA collection only after a judge or a grand jury makes a probable cause determination and the arrestee is charged with a qualifying crime. Some states that require a probable cause hearing provide an exception if the person was arrested pursuant to a warrant.
Juvenile cases. In some jurisdictions, pre-conviction DNA collection applies to both adults and juveniles. Other states restrict the application to juveniles who were arrested on a warrant or are a certain age (usually 16 to 18 years).
What Happens if You Refuse to Provide a DNA Sample?
Jurisdictions take different approaches when an arrestee or a defendant refuses to provide a DNA sample. For example, some states require the arrestee's consent, and there's no penalty for refusing to provide a DNA sample. However, the federal government and many states authorize law enforcement to use reasonable force to obtain a sample. A court order may be required before the authorities can forcibly collect a sample. In some jurisdictions, refusing to give a DNA sample is a crime itself, punishable by imprisonment and a fine.
Other Ways Law Enforcement Can Search for DNA Matches
Some DNA searches don't require a conviction, an arrest, or even a search warrant. That's because people often provide their DNA voluntarily to private companies, or leave it behind in places where the police can collect it without needing their permission.
Consumer genealogy databases. Courts have generally decided that, when a customer shares their DNA with a genealogy company, they lose their Fourth Amendment right to keep the sample (and the resulting DNA profile) private. That doesn't mean those companies can automatically share a person's DNA profile. But it does mean there are many fewer legal constraints than there would be if the police wanted to collect DNA from an individual who had not been arrested or convicted of a crime. The main limits are:
- the company's own terms of service, which must explain when (if at all) the sample can be shared with third parties; and
- state law, which can provide greater protections than the minimum required by the United States Constitution.
As of early 2026, only Montana requires the police to get a search warrant to access DNA profiles on genealogy websites. Some other states don't require a search warrant, but place other legal limits on how law enforcement can search genealogy databases. For example, the law in Maryland requires judicial authorization and only allows searches for cases involving certain serious crimes. In many states, though, only a company's terms of service limit law enforcement access to customers' DNA profiles. That doesn't necessarily mean the protections are flimsy, though. For example, some companies require the police to have a warrant or a court order before they'll share a customer's DNA data.
Familial DNA analysis. Sometimes the police can identify a criminal suspect by first identifying the suspect's relatives. That's because relatives share some genetic information—the closer the relation, the more similar the DNA. So, for example, a state might take a DNA sample from a crime scene and compare it to samples in government databases. If there isn't a direct match with a specific person, it's still possible that familial DNA analysis can identify a suspect's close relatives and help narrow the search.
Similarly, sometimes the police can use information on genealogy websites to find relatives of a suspect. In 2018, this approach helped California police identify and arrest the Golden State Killer. Investigators used DNA from a crime scene to link the killer to distant relatives who had uploaded their DNA profiles to a genealogy site.
"Abandoned" DNA. In 1988, the Supreme Court ruled that people don't have a right to privacy when it comes to trash they leave by the curb for pickup. The reasoning is that, once someone has abandoned an item in a public place, they can no longer have any expectation of privacy when it comes to that item. (California v. Greenwood, 486 U.S. 35 (1988).)
The Greenwood case was decided long before DNA collection and testing by law enforcement became routine. But, in the years since Greenwood, courts have built on this idea and ruled that a person does not have a right to privacy when it comes to traces of DNA they leave behind in public. The law on this question is still evolving. But, in general, courts don't think the police need search warrants to retrieve and run DNA tests on, say, a soda can a person has drunk from and then thrown away, or household items they put out with their trash.
This logic applies to items that people deliberately abandon (for example, by throwing them out). It also applies to items and surfaces that contain DNA a person has "shed" by, for example, leaving traces of saliva on a coffee cup or traces of sweat on a chair. DNA profiles derived from these "abandoned" samples can then be compared to profiles in DNA databases.
How DNA Samples are Stored and Accessed
The National DNA Index System (NDIS) is the national DNA database, which contains DNA profiles from participating federal, state, and local forensic laboratories. The Combined DNA Index System (CODIS) is the program the FBI uses to analyze DNA data. The collection and storage of these profiles by the federal government has raised concerns about privacy, and how the profiles might be misused. To address these concerns, the CODIS database is covered by rules designed to limit what information is stored and how it can be accessed and used. For example:
- CODIS only stores enough DNA information to identify the person it belongs to, but not enough to provide information about, for example, how a person's genes could impact their health.
- The database does not store a person's DNA profile together with their name or other personal information. If a sample in the database matches one collected from a crime scene, it's still necessary to ask the lab that originally collected the sample to provide details about the person from whom it was collected.
- Access to CODIS is limited to investigators using it for law enforcement purposes.
In some states, DNA profiles are automatically submitted and entered into the national database. Laboratories that submit DNA data to NDIS must meet certain requirements, including accreditation and undergoing audits to demonstrate compliance with FBI standards. Private laboratories don’t qualify to submit DNA data to NDIS. At the state level, DNA is stored in databases that are operated by either:
- private laboratories
- government agencies associated with law enforcement, such as the Department of Justice and Department of Public Safety, or
- government agencies not directly affiliated with law enforcement, such as the Department of Health.
Expunging a DNA Sample and Profile
Most jurisdictions that authorize pre-conviction DNA collection have an expungement process, which involves removing an arrestee’s profile from the database and destroying the DNA sample. In some states that have these procedures, the person’s sample is destroyed, but the profile remains in the database. There can also be significant practical hurdles to getting genetic information expunged from government databases.
In some states, expungement of a DNA record is automatic. In other jurisdictions, the arrestee must request expungement of the record. Generally, an arrestee qualifies for expungement if:
- the arrestee isn’t charged with a qualifying crime
- no probable cause existed for the arrest
- the charge is reduced to a crime that doesn’t qualify for DNA collection
- the charge is dismissed, or
- the arrestee is found not guilty.
Under post-conviction DNA laws, a defendant typically qualifies for expungement only if an appeal or other post-conviction relief is successful.
Learn More About DNA Evidence in Criminal Cases
As we've discussed, the federal government and the states all have their own rules for DNA collection in criminal cases. And, while DNA collection and testing is now a well-established part of criminal investigations and prosecutions, courts and legislatures are still deciding how the law should apply to specific situations. So, if you have questions about your own situation, it's important to know the current law where you live, and to consult an attorney if necessary.