DNA and police

When can the police take my DNA?

The laws for police powers to collect DNA vary widely across the world. In the UK, the police can take your DNA upon arrest for most offences, using a mouth swab, without your permission. Permission however, is required for intimate sample collection for particular crimes, such as rape.  This will usually happen at the police station, after which the sample is sent to a laboratory to extract the DNA and create a forensic DNA profile. This is a string of numbers based on parts of the DNA, which can be stored on a computer. This DNA profile is repeatedly run through the criminal database to see if there is a genetic match to an existing stored DNA profile. Stored DNA profiles include those collected from crime scenes and from individuals. The UK has one of the largest criminal DNA databases on the world. The routine sampling of DNA upon arrest raises controversy, especially with regard to children. Previously all DNA profiles were stored indefinitely on a criminal DNA database, but a new law was adopted in 2012 that requires DNA profiles from all those found to be innocent of a crime, to be removed. DNA samples taken from known individuals must also be destroyed, six months after the computerised DNA profiles have been obtained from them, or when they are no longer needed for an investigation.

In France, DNA collection from arrestees is also routine, and can include children as well as protesters. South Africa is similar, allowing for expansive collection of DNA from suspects. 

In the US, there are differing local state laws, with around half of states allowing DNA collection if you are arrested, while others require additional oversight. Idaho for example, requires a court order or conviction before DNA can be collected. Some states automatically remove DNA samples after a person has been found innocent of an offence, while in other states, you have to request that your DNA samples are removed from a police database. 

Many other countries have different policies. For example, most European Countries do not perform routine collection of DNA upon arrest. Instead, there is some sort of oversight in place, such as a decision to charge a suspect, or a judicial requirement for an order from a court. In Norway and Germany, court orders are required, and are only available, respectively, for serious offenders and for those convicted of certain offences and who are likely to reoffend.

Some nations are in the process of updating their laws to increase genetic surveillance. India, for example, is in the process of drafting a new law that may allow for the collection of DNA from arrested suspects, though the laws are yet to be finalised and face challenges from the public over privacy concerns, and potential discrimination against marginalised groups. 

How can my DNA be used in evidence?

When your DNA is taken by police, it will be processed to see if it matches a DNA profile taken from the scene of a crime. It is also run through a forensic DNA database to see if it matches existing profiles. If there is a DNA match with a crime scene DNA profile, it may be used in court as evidence. In many countries, DNA evidence alone is not sufficient to secure a conviction, but sometimes people are convicted on the basis of a DNA match alone, particularly in the United States. Often, the DNA results are not straightforward to interpret: for example, the DNA profile from the crime scene may be degraded, contaminated, or contain a mixture of more than one person’s DNA. Depending on the circumstances of the case, DNA may have been left at the crime scene before the crime took place, or have been transferred there afterwards, and thus other factors should be taken into consideration. 

The majority of criminal cases do not involve DNA evidence. However, in some cases, if there is no match with a DNA profile believed to have been left at the crime scene by the perpetrator of the crime, then it is expected that any case would be dropped against the suspect. If a match is found in such cases, this is usually considered the gold standard of forensics testing and is heavily relied upon in courts. The testing however, is not always 100 % accurate. Many miscarriages of justice have resulted from errors, often as a result of contamination of evidence in the lab or crime scene, exposing flaws in the quality and accuracy of DNA profiling. The courts may also rely matches with a partial crime scene DNA profile, or with a mixed profile, which are less reliable. While it is generally agreed that the quality of such testing methods should be strictly regulated, oversight across the world is still generally lacking. There is a need for quality assurance at the crime scene, as well as the laboratory, to ensure crime scene DNA is correctly tracked and labelled and not contaminated. 

Additional concerns regarding the accuracy of DNA evidence are due to the growing size of DNA databases in many countries, increasing the chances of a false-positive match. A false-positive match is an exact match between two DNA profiles which occurs by chance, even though the DNA comes from different people. False-positive matches can occur because forensic DNA profiles are based on only parts of a person’s DNA and are therefore not unique to an individual. They are more likely to occur in cases where the innocent suspect is related to the perpetrator and therefore shares some of the same DNA.

Even in the UK, which has the largest DNA database per head of population, most DNA matches occur between known suspects (for whom other evidence has already identified them as a suspect for a crime) and stored crime scene DNA profiles. However, in a minority of cases, a match on the DNA database will identify a new suspect who has not been previously linked to a crime. Whilst this demonstrates the ‘added value’ of having a DNA database, such matches could also lead to miscarriages of justice if the individual is assumed to be guilty based on DNA evidence alone.

Can my DNA be collected at borders?

DNA testing at borders has become more of an issue in recent political climates, prompting human rights concerns for immigrants and those seeking refuge or asylum with regard to state surveillance and discrimination against marginalised groups. 

In the US, DNA testing was first introduced to verify family connections for immigration purposes in 2000. For such cases, DNA testing is voluntary, though immigration officers are allowed to suggest testing be performed if other evidence of family relations is deemed insufficient, or is unavailable, for example birth certificates. Since 2018, DNA testing has been used when reuniting thousands of children separated from their families at the border under the ‘separation’ policy, in order to charge parents with illegal entry. This policy moved the focus to DNA testing as the go-to method to prove relations rather than relying on alternative means such as gathering paperwork.  Little public information on how such DNA would be stored, and retained has been published. Unfortunately, it remains unclear if all children were successfully reunited with their families. Although the separation policy has now ended, voluntary rapid DNA testing has since continued for proving family relations. Compulsory DNA collection is also performed by US immigration control for people seeking refugee status and seeking asylum from 13 specified countries: Afghanistan, Burundi, Central African Republic, Cuba, Democratic People’s Republic of Korea, Democratic republic of Congo, El Salvador, Eritrea, Ethiopia, Guatemala, Honduras, Iran, Iraq, Mali, Somalia, South Sudan, Sudan, Syria. In 2020, laws went into effect that require DNA collection from immigration detainees, which is stored in the Federal Bureau of Investigation’s (FBI) criminal DNA database, despite people not committing a crime.   

In the UK, DNA testing is not mandatory, but there have been experiences where DNA testing was nonetheless illegally demanded in some cases. In 2009, the UK government piloted ‘The Human Provenance Pilot Project’. Under this project, people seeking asylum in the UK were asked to provide DNA evidence of geographical ancestry, for example proof that Somali asylum seekers arriving from other countries, were indeed Somali. To do this, ancestry testing was performed to attempt to identify people’s nationality, despite deep scepticism from geneticists of the scientific basis of such a program. It is a basic misconception that someone’s genetics would align with any national border. Following extensive criticism of the program, it was later cancelled. In 2018, it also became evident that immigration decision-makers were mandating DNA based evidence for immigration purposes, despite a lack of legal power to do so. It has since been clarified that while DNA evidence can be used to prove family connections, such DNA evidence cannot be asked for, or required for immigration decisions. However, voluntary testing can be submitted to assist the application, encouraging applicants to pay for costly tests. 

In the EU, DNA testing is allowed for reunification of families, and in some countries such as Spain, it is widespread.

In Israel, it was revealed by media in 2013 that DNA was being taken from immigrants arriving from African countries. A police request to collect DNA samples was already rejected by government, but police later had collected samples anyway. The police did this by charging immigrants with illegal entry, thus justifying taking DNA as part of a ‘security-related’ crime. 

Can the police store my DNA records on a database?

The following summary is up-to-date at the time of writing. More recent developments are available on: http://dnapolicyinitiative.org/

An estimated 70 countries in the world have forensic DNA databases, focused mainly in Europe, North America, Australasia, and East Asia. The laws on whose DNA is collected and stored, and for how long, vary between countries.

Some of the largest databases are in China (estimated at more than 68 million, about 4.5% of the population), the USA (14.4 million, also about 4.5% of the population) and the United Kingdom (5.7 million, 9% of the population). The United Kingdom has the highest proportion of its population on the database, despite having shrunken in size following a successful campaign to remove innocent people’s and some children’s DNA profiles from the records in 2012. This is in line with all 47 European countries which are members of the Council of Europe (and hence also subject to the European Convention on Human Rights), as well as other most other nations worldwide (such as South Africa, South Korea and Malaysia), which have included provisions to delete innocent people’s DNA profiles in their DNA database laws. 

All European Union member nations are required to have national police databases, but laws on whose DNA is collected and stored vary in different European countries. Following a judgment by the European Court of Human Rights in 2008 (in a case known as ‘S and Marper v United Kingdom’), all 47 member states of the Council of Europe must restrict retention of DNA profiles on police databases to what is necessary and proportionate. This means that innocent people’s DNA profiles and biological samples can only be stored for limited amounts of time.

In the UK, while most records are now deleted if you are not convicted, the record is still kept for 3 to 5 years for certain serious crimes, or even indefinitely if the case is deemed a ‘national security’ threat. Similarly, in many countries, DNA profiles can be retained temporarily if it is decided that suspicions remain about someone, or they are involved in another case. For all adults convicted of a crime, records are kept indefinitely in the UK. Currently, even for cautions, which are issued by police to people who admit guilt without the need for a trial, profiles are retained for 100 years. However, some time limits on the retention of DNA profiles for people convicted of minor crimes are expected to be introduced following a judgment by the European Court of Human Rights in a case in Northern Ireland. Some children convicted of a single minor crime already have their DNA profiles automatically deleted.

In the US, DNA can also be taken upon arrest in some states, with profiles stored on a local database, and also on the national FBI database called CODIS, that links individual state and federal databases. While only 30 individual states allow for collection upon arrest, some individual databases built by local authorities are not subject to state rules, with little oversight and control over police DNA collection. A growing number of police departments are amassing large genetic databases. Police authorities in New York City, despite state law requiring a conviction before DNA can be taken, are nonetheless collecting DNA from arrestees and even children who are questioned. One example is that of a 12-year-old boy who was being questioned for a crime that was later dropped. Police gave the child a can of soft drink, which was later used to extract a DNA sample. New York City police forces have since pledged to delete records of innocent people’s DNA, though this yet to be carried out. Some individual states have laws to remove innocent people’s DNA following a lack of conviction, including Maryland, North Carolina, Tennessee and Missouri.  

In Canada, the database has also expanded over the last 20 years, with over 400,000 profiles of convicted offenders on the system. Canada however, does not take DNA upon arrest, unlike the US and UK, though there have been recent discussions to move to such a model. Canada does not retain DNA from young offenders, though profiles of convicted people remain indefinitely. 

Police can also gain access to commercial DNA databases in some circumstances. There are examples in the United States of police accessing consumer ancestry databases owned by private companies (see If I buy a DNA test online, is my information private?).

Can I get my DNA records destroyed?

In the UK, if your DNA was taken upon arrest, but you were not charged or have since been exonerated of the charge, then your DNA profile should be automatically deleted from the DNA database.  However, there are some exceptions. For some people arrested for serious offences, police may justify keeping DNA records for up to three years (plus a 2 year extension if granted by a District Judge), and for others, they may be kept for a renewable two year period (perhaps indefinitely) for ‘national security’ reasons. Children convicted of a single minor offence also have their DNA profiles removed from the DNA database. If you have a conviction as an adult then the record will be stored indefinitely, but this policy is now under review. Many other countries, such as South Africa, also have established procedures for the automatic removal of DNA profiles taken from innocent people from their DNA databases.  

In the UK, it is also possible to apply for the early deletion of DNA records by filling in an application to the National Police Chiefs’ Council. Other countries, such as New Zealand, also have procedures in place to allow people to apply for records to be deleted. However, such procedures can be difficult to use and on their own they are inadequate to prevent most innocent people’s DNA profiles from being stored indefinitely.

Destruction of the biological samples taken from known individuals, once the computerised DNA profiles have been obtained from them, is an important privacy protection. This is implemented in many but not all countries with DNA databases. In the UK, everyone who has their DNA sample taken by the police has this sample destroyed, usually after six months (to allow time for quality assurance checks), but it can take longer if samples are needed for a complex court case. In contrast, crime scene DNA evidence, including biological samples from unknown individuals, is usually retained as it may be needed for a reinvestigation some years in the future. 

In the US, the national law only requires that DNA profiles can be destroyed after receiving court orders. If you live in a state that does not require the automatic removal of innocent people’s DNA, then such notifications are not sent unless the individual makes an application for removal or brings a legal case. Long court battles have taken place to get innocent people’s DNA removed from databases. One example of a 12-year-old boy in New York State whose DNA was taken from a soda can given by police, the family had to go through a year-long legal process to get it removed. 

Can my DNA exonerate me?

In the case of appealing a conviction, re-analysis of crime scene DNA samples can be performed and compared to your own DNA to prove innocence. For reversing such miscarriages of justice, collection and preservation of crime scene DNA is crucial. In contrast, retention of individuals’ DNA records plays no role in exonerating people, since the innocent person carries their DNA with them at all times and this can thus can be compared to crime scene DNA without needing to be kept on a DNA database.

Examples of ‘DNA exonerations’ include the Innocence Project in the USA, which has been involved in the freeing of 365 people who were wrongfully convicted as later shown by re-analysis of their DNA. 

Could I be wrongly convicted of a crime due to a DNA match?

DNA is usually an accurate way of identifying people, but it is not foolproof.

There are various examples of cases where DNA matches have led to wrongful convictions. There are numerous ways in which this can happen, either by unintentional contamination of DNA samples, incorrect interpretations of the genetic data, or falsifying evidence to frame people. Moreover, partial matches of DNA can lead to wrongful convictions. This can happen if only part of a DNA profile can be lifted from the crime scene evidence, or if the sample contains DNA from more than one person (this is common in rape cases). The risks are amplified by larger DNA databases, increasing the chances of an incorrect match. 

There are also examples of miscarriages of justice resulting from genetic contamination, which could happen at the crime scene, or in the forensics laboratory. Such problems warrant high standards of laboratory practice and quality assurance, though global standards currently vary. A man in the UK was held in custody for 5 months for a rape charge, after giving DNA following a ‘spitting incident’.  His DNA sample contaminated that of the victim’s body swab samples, after the same plastic container was mistakenly used to store both samples. Despite him being hours away from the victim at the time of the crime, it was only after phone records proved this to be true, that the case was dropped. 

Interpretation of genetic data is not straightforward. The quality of DNA may be low, giving only partial information. Samples may contain a mixture of individual people’s DNA. This can be complicated by all sorts of additional factors, even for example, that some substances such as nail polish may preserve DNA for longer, leading to numerous people’s DNA becoming stuck to someone’s finger nails. Such details led to a wrongful conviction in the UK, where a partial match was made to a sample under the nail clippings of a crime victim, which was also carrying DNA from other people. The innocent man also suffered from a flaky skin condition that meant he shed more DNA than usual, and his DNA could have been picked up from a surface the victim had touched. As the use of genetic evidence grows, such cases illustrate the complexity of forensic genetic science, and also highlight the need for supporting evidence to be used alongside any forensic evidence in criminal cases. 

Can I find out if my DNA is on a police database?

In the UK, if you want to find out if your DNA is on the police database, you can make a ‘subject access request’ to the Criminal Records Office, which is free of charge.  This will tell you if you are on police records, and if they have fingerprint and DNA data stored. All European Union (EU) countries have a similar process, as a result of EU data protection laws. Many, but not all, countries worldwide have similar privacy or data protection laws, which allow citizens to check if their personal information is stored on a database.

Can my DNA records be shared internationally?

Many countries have agreements to share forensic databases. For example, European Union member states have committed to an EU-wide sharing of DNA database matches under the Prüm Convention. 25 of the 26 member states have implemented this to date. Internationally, countries can also send DNA profiles to a database managed by Interpol. DNA laws in many countries allow for the international exchange of DNA profiles with other countries. The level of legal safeguards can vary widely.  The US has also established agreements for cross-border exchange of forensic data with countries including Belgium, Austria, Switzerland, the Czech Republic, Germany, the Netherlands, Finland, Spain, Estonia, Greece, Denmark, and also South Korea. However, in practice, these agreements are currently only used for fingerprints.

Is my DNA profile stored securely?

Some countries have privacy laws to limit access to genetic data and how it may be used. Privacy laws vary widely. In some countries, even if such laws exist, they do not apply to data collected by the police or used for policing purposes. In the UK and in the European Union (EU), there are some differences in the data protection laws that apply to databases held by the police and security services, compared to most databases.  The USA does not have comprehensive national privacy laws, and legal protections vary from one state to another. Other countries with DNA databases, such as China, do not have privacy legislation, nor do some countries in the process of developing police databases, such as India. Privacy laws are still under development in both these countries.

Most countries with police DNA databases have a DNA database law which restricts the use of the database to certain purposes, and limits access. However, the level of safeguards can vary, as can the penalties for unauthorised access or misuse.