Dr. Moissidou Despina
(RIEAS Senior Analyst and a Former Crime Scene Investigator Greater Manchester Police, UK).

Copyright: www.rieas.gr

The use of DNA (deoxyribonucleic acid) in the detection of crime, the last decade, can be considered a major breakthrough, as the introduction of fingerprints was in the previous century. DNA is found in the nuclei of the cells of any organic matter, such as humans, plants and animals, and it contains the chromosomes which “carry” our inherited characteristics. It is unique for each person (except in the case of identical twins), it is the essential component of every cell in our body, and it is passed from one generation to the next; but what is more interesting is that it contains the invaluable genetic information of the person. A person inherits half of the DNA from the mother and the other half from the father, in a variety of combinations. The most important thing in the use of DNA is that its molecular differences in each individual can be demonstrated, and a profile can be created.

The recognition of the above revolutionary benefit of DNA led the scientists to the idea of creating a database, like that for fingerprints. That idea meant the recovery of DNA samples from a crime scene, in order to trace suspects, and then storage of the information extracted from the samples in a database for future reference. Eventually this idea became practice, and soon it was realised that DNA was a powerful tool in the solution of many crimes, from burglaries and vehicle thefts to major incidents, such as murders and terrorist attacks.

More precisely, DNA Database is a police forensic database where genetic information and personal data is stored, from individuals involved in various crimes, and scene samples recovered from crime scenes. When a sample arrives at the laboratory, the scientist analyses some areas of this sample and creates a so-called DNA profile (The Forensic Science Service, 2003). This profile is unique for each person, but if there is a match (person to person or person to scene), it is either because two persons are related (such as identical twins) or the profile is incomplete.  Otherwise the chances of getting a match from two different profiles is very low. Of course, there is always the issue of contamination or degradation of the sample, after it is taken from the scene or the person related with the offence or a volunteer.

DNA can be extracted from any human tissue left at the scene (as long as it contains cells), such as blood and saliva, left in any place i.e. cigarette end in an ashtray or tiny drop of blood on the carpet (Williamson & Duncan, 2002). Thus, when a sample is collected and analysed it is compared with the profiles in the DNA database: a) there can be a match with a person who is on the database, so there is a potential suspect either for the case examined or an unsolved one; b) a person’s profile matches another individual’s profile indicating these two people are the same person or; c) two cases can be linked without a suspect identification.

At the crime scene, police can take samples from the crime scene through Crime Scene Investigators, who are trained to obtain potential DNA samples with a reduced risk of contamination, i.e. wearing protective equipment, using sterile swabs with sterile water. Samples include semen, blood, saliva (from cigarettes, drinking glasses, chewing gums), hair and urine (Linacre, 2003).

Samples that are taken from individuals are called Criminal Justice (CJ) samples and they are taken from persons arrested by police. For the purpose, a mouth swab is rubbed inside the cheek, or ten plucked hairs with good roots removed from the head (also depending on the circumstances twenty five hair from all over the head can be recovered). For each case samples are obtained twice (The Forensic Science Service, 2003). Then the samples are placed into sterile plastic tubes with a unique barcode and sealed appropriately.

The police use DNA samples in various ways: a DNA sample taken from a scene can be compared with a sample taken from a suspected individual; moreover, persons arrested for an offence are required to give a DNA sample, which can be searched against profiles of the DNA database for any unsolved crimes; also various crime scene samples can be compared together, useful for intelligence information (ACPO).

In Great Britain, with the approval by the Home Office, police has the right to get non-intimate samples (mouth swab and hair) without the individual’s consent and that a suspect can be charged as “ long there is further supporting evidence” (Home Office, 2004). We should mention here that DNA can not be used as conclusive evidence, unless there is complimentary evidence such as fingerprints. The reason is that despite its uniqueness, DNA technology can not provide a 100% match certainty from a sample taken. 

In the lab, one of the CJ samples is kept frozen and the other is used for the DNA profile, through a process called Polymerase Chain Reaction. The data is analysed by computer and the result is loaded onto the DNA database. When further profiles are loaded onto the database, the computer compares them with the existing profiles in its memory and prints out any matching results (The Forensic Science Service, 2003). However, a match is not a proof that the particular suspect is responsible for the specific crime. Moreover, in UK, a scientist is requested to testify in court, when the value of DNA evidence requires further clarification (Home Office, 2004).

There are several DNA techniques, and some of the common ones used for DNA profiling are: Short Tandem Repeat Profiling (STR), which examines the length of the repeat units and the lengths are presented in a digital format, the so-called DNA profile; Low Copy Number (LCN), which can be used when the amount of DNA is very small or highly degraded, however it is very sensitive and there is an increased risk of contamination; Mitochondrial DNA can be used for decomposed material, however, it is less powerful in profiling individual since is inherited down the maternal line. Also, it is not comparable with STR profiles so it can not be loaded on the database; Y-Chromosome Short Tandem Repeats (Y-STRs) can be particularly useful in the investigation of sexual assault cases, as the Y chromosome do not occur in females, it is present in male DNA.

There are other techniques as well, such as familial searching, which has to do with family relationships. England and Wales legislation is considered to include some of the most permissive laws globally with regards to the use of DNA. Legal history goes back to 1984, where police were allowed to ask doctors for blood samples with the individual’s consent; in 1993 DNA database was recommended by Criminal Justice, while in 1994 the Home Office commissioned the Metropolitan Police to perform a study of a forensic database and its result helped in the creation of the NDNAD (Asplen, 2004). In 1997 non-intimate samples were allowed to be taken without consent from persons still in prison (Werrett, 1997); in 2001 Police and Criminal Evidence Act allows samples to be kept indefinitely, and in 1995 the extension in Criminal Justice Act allows police taking non-intimate samples without consent and keep the data extracted indefinitely.

According to England and Wales law (Scotland has a different law for DNA database), everyone, who is a suspect, or has been arrested or has committed a recordable offence, can be included in the NDNAD, and the individual’s profile remain in the database indefinitely. The above powers entitled by the law have raised concerns with regards to the civil rights, since the database includes genetic information of individuals who have not been convicted. Also, any misuse of the database could have false effects in the investigation of a case. Even though the law is clear on the use of the DNAD and related issues, there are still concerns, especially for the future use of DNA as technology develops rapidly and the risks of manipulating personal information by using new techniques could increase.

The use of a DNA database has started being under a lot of scepticism by many people, including scientists, and is related to issues such as who should be included in the database, how samples should be handled, who decides on the function of the database and possible use of genetic information for future reference. Keeping persons who might commit a crime repeatedly might help crime prevention. However, offenders could face problem in rehabilitation programmes, if their profiles are kept permanently. In addition, volunteers and people participating in mass screening are put in the database. These groups could be treated as ‘suspects’ and probably there is no reason why they should be kept in the database. “Being listed could jeopardise employment or foreign travel, and the information could be used for research on topics such as the genetic correlates of ethnicity or criminal behaviour, for example”, Anna Gosline had written on New Scientist (New Scientist, 2005). Maybe there should be establishment of an independent ethics committee could introduce guidelines for the safer use of the database and the protection of human rights. However, we should not overlook the benefits of the use of DNA, as it has brought results on cases that common investigation procedures could not bring forward.

DNA is a powerful forensic tool in crime detection, and justifies its use by the police. Unlike a fingerprint DNA can potentially indicate: who a person is related to, what a person looks like and possibly if that person is at risk of some genetic condition (DoH, 2002). Its potential for the future, due to the genetic information it can reveal, will gradually lead enforcement agencies to the quick arrest of criminals and eventually, with the help of technological developments, its use as conclusive evidence in the courts of law for their conviction.

However, this coin has two sides: the power of DNA technology can equally become a weapon in violating human rights, can support uncontrollable medical research for profit, can be used as means for a minority group to gain power and, of course, can be misused by police forces for their own purposes. Because of the above, a need has been emerged in order to control its practicalities, protect people and reinforce strict guidelines for its safe use.

First of all, the storage of DNA samples should be reconsidered as to which and if these samples should be stored indefinitely, so to reduce the risk of using them for any other type of research. Moreover, there should be an encouragement in further studies for the use of this database in the legal system, in order to avoid misinterpretation.  Accordingly, an independent body could make recommendations of accessing the data for any purposes. Furthermore, the DNA information of individuals who are either innocent or not charged should be given the most of attention, as their data could be misused without their consent; maybe the consideration of that information being removed, when a case is closed for instance, is a good option.

Last but not least, the rapid development of sensitive DNA techniques, such as Low Copy Number, STR and others, and their application in forensic science should be viewed as a major benefit for the public, and not for anything else, as the impact of the use of DNA on the detection and reduction of crime is huge and the balance between its use and misuse is fragile.


- Association of Chief Police Officers, 2005 DNA Good Practice Manual, London: ACPO.
- Asplen C.H., 2004: The Application of DNA technology in England and Wales. US Department of Justice,   USA: Smith, Alling Lane.
- Department of Health (UK), 2002: Forensic uses of personal Genetic Information. Inside information: Balancing interests in the use of personal genetic data. London: DoH, pp. 145-60.
- Gosline A, 2005. Will DNA profiling fuel prejudice? [online]. New Scientist.
- Home Office (UK), 2004 Charges on Basis of Speculative Search Match on the National DNA Database:  circular58 [online] London.
- Linacre A., 2003: The UK National DNA Database. The Lancet, 361, pp. 1841-2.
- The Forensic Science Service, 2003 National DNA Database Board. The National DNA Database Annual Report 2002-03. Forensic Science Service: London.
- The Forensic Science Service, 2003. Mouth Swab to database: A guide to the DNA profiling process: a factsheet. The Forensic Science Service, London.
- Werrett DJ., 1997: The national DNA database. Forensic Science International, 88, pp. 33-42.
- Williamson R. and Duncan R., 2002: DNA testing for all. Nature, 418, pp. 585-6.

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