What happens to my DNA?
Your DNA and fingerprints can be left wherever you go, for example on a glass that you have been drinking from. Your DNA contains a string of chemical letters that can be used like a code to identify you. Because you share half your DNA with your parents and with your children it can also be used to identify your relatives (for example, by doing a paternity test).
Taking your DNA
If you have been arrested, your DNA will be taken using a mouth swab (which collects some cells from inside your cheek) while you are at the police station. If you refuse, the police may use ‘reasonable force’ to pull some hairs out from your head to get a sample of your DNA. Two samples are taken and sent to a laboratory. One sample will be analysed and the other stored. This now happens routinely to anyone aged ten or over who has been arrested for any ‘recordable’ offence. This includes most offences except dropping litter or parking offences. In most cases, DNA is not relevant to the offence being investigated.
Storing your DNA sample
In England and Wales, DNA analysis has been privatised. As well as analysing the samples, the companies involved are also paid to store the second (spare) sample taken at the police station. These samples contain some sensitive genetic information, including some information about your health. In the past, the companies have used some of these samples to do genetic research without telling people or asking their permission. This practice is currently suspended, but it has not been banned.
Your record on the National DNA Database
The laboratory analysis creates a string of numbers known as a DNA profile, which is stored on a computer database called the National DNA Database. The numbers in your DNA profile are based on some of the chemical letters in your DNA. Your record on the National DNA Database contains some other information about you, including your name and your ‘ethnic appearance’ to the police officer who arrested you.
At a crime scene, samples of blood or other bodily fluids, including spit on cigarette butts or semen from a rape, are collected and analysed in the same way as your DNA. DNA is collected from only a very small proportion of crimes: most are burglaries and car thefts, rather than rapes or murders. Many of the samples taken from a crime scene may not be from the person who committed the crime. Some samples will have come from the victim and others from passers-by or witnesses. Some will have been left there earlier in the day.
In most cases, the police do not need your or your child’s DNA to investigate the crime for which you or your child have been arrested. But if the police add your DNA profile to the database they can check whether it matches any stored DNA profile from a past crime. If they keep your record on the database they can also check whether it matches any crime scene DNA profile that they collect at any time in the future, throughout the rest of your life.
DNA matches are not foolproof
Very rarely, false matches between the DNA profile of someone on the database and a crime scene DNA profile are expected to occur by chance, because only parts of your DNA are analysed. False matches are much more likely if the crime scene DNA profile is not complete, or if you are related to the person who committed the crime (because your relatives’ DNA is similar to yours). False matches are expected to become much more common when the police start making DNA matches across Europe, which the Government has agreed to do about two years from now.
Many more matches with innocent people’s DNA profiles occur because the DNA collected from the crime scene may not be from the criminal: it could be from the victim or anyone else who was there during the day, or it could be planted (for example, on a cigarette butt).
If your DNA profile matches a crime scene DNA profile, the police are informed of the match and may treat you as a suspect for that crime.
Your record on the Police National Computer
The computer records on the DNA Database are also linked to your stored DNA sample, using a unique barcode number, and to another database called the Police National Computer.
Like the DNA database, the Police National Computer also used to be a criminal database, but since 2006 all the records on it have been kept permanently. This means that you will probably have a permanent record of your arrest, which could be shown to a future employer even if you have done nothing wrong. Foreign governments also sometimes check these records, for example if you apply for a travel visa.