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Fighting crime with DNA

01 June 2007

The UK has the largest forensic DNA database in the world, containing profiles from over three million individuals. New uses are being made of this information, but the public has been given little opportunity to discuss the civil liberties issues involved.

The use of biological information such as DNA fingerprints is now a routine part of solving crime. In early 2007, the RSC and the Bioscience Federation jointly submitted evidence to a Nuffield Council on Bioethics study and recommended that the scientific community must engage the public in a debate on what is technically possible and ethically desirable.

The UK has the largest forensic DNA database in the world, containing profiles from over three million individuals. These have been taken from people who have been arrested for a recordable offence. No consent is required and such samples remain on the database even if the person is not charged.

Forensic use of DNA

Biological samples collected from crime scenes are compared with samples stored on the National DNA Database. In addition, the police use DNA samples to reveal information about individuals that may lead to their detection, such as their gender and ethnic background.

They can also compare samples to data from the National DNA Database to identify any close family member whose DNA may already be stored on the database. The first UK conviction based on familial DNA searching occurred in 2004 with the conviction of Craig Harman of Frimley, Surrey, for manslaughter. A search of the National DNA Database identified a close relative whose profile matched that from the crime scene for 16 out of 20 indicative results, which is considered a very strong match. A subsequent sample given voluntarily by Harman proved an exact match.

Interpreting bioinformation

DNA profiles can be derived from minute samples of saliva, blood and semen recovered from crime scenes. The technique currently used in the UK for DNA profiling is SGM PlusŪ. It looks at 11 markers (10 markers plus a gender indicator) to give a DNA profile. Each marker indicates a Short Tandem Repeat (STR). STRs are short sequences of DNA that are repeated several times within the human genome. The sequence of these repeats is unique to each individual.

The statistics

The probability of a random match between unrelated individuals using SGM PlusŪ is on average less than 1 in 1 billion. To date, there have been no chance matches between full SGM PlusŪ profiles from unrelated individuals. False chance matches are more likely to arise where only partial profiles have been obtained due to degraded samples or where only very small quantities of DNA are available to test.

The use of only 10 SGM PlusŪ markers does raise statistical issues. Although the practise of multiple testing is adequate to pick up errors, it will not trap rare instances of true chance matches. A move to testing for a larger number of markers would substantially reduce the likelihood of this event.

The European Network of Forensic Science Institutes is currently looking at potential additional markers to improve the discriminating power of profiles. It hopes to expand typing to a 13 - 15 marker system in the next year or two, which will substantially reduce the likelihood of false chance matches. 

International collaboration

Criminals offend outside their national boundaries, so it can be necessary to exchange DNA data between countries. Currently this is done through Interpol on a case-by-case basis.

In the UK, strict protocols are followed throughout the collection and analysis of DNA. But not all countries have the same safeguards. We need international standards for the collection and storage of genetic profiles to protect civil liberties and facilitate profile exchange between countries.

"what is the value of forensic bioinformation if police, legal professionals, witnesses and juries don't understand it?"

Within Europe, the European Network of Forensic Science is attempting to standardise DNA profiling by identifying common STR markers. Currently only 7 are common to all European institutes and this is not enough for accurate identification.

Ethnicity and geographic origin

SGM PlusŪ provides only weak information on ethnic and geographic origin. Research is ongoing to identify single nucleotide polymorphisms (known as SNPs - a variation in a single DNA base-pair) that indicate major population differences. Such information would provide the sort of ethnic and geographic information that might be useful in identifying suspects.

Obviously this could be a powerful tool, but such information would need to be used with caution. For example, witnesses judgements of ethnicity based on appearance may not always accurately reflect the DNA profile. Such tests could lead police to incorrectly discount certain suspects or follow other blind alleys.

Personal and medical privacy

DNA profiling also has the potential to reveal sensitive personal information, such as previously unknown family relationships. SGM PlusŪ profiles currently provide no information of a medical nature, although it has been suggested that one marker may be associated with type I diabetes.

In its response to the Nuffield Council study, the RSC recommended that information contained within the National DNA Database should be limited to that required for identification purposes only and should not seek to provide any other type of information. With this in mind, we see a need for further legislation to ensure the confidentiality of genetic information acquired by the state.

Bioinformation as evidence

Interpreting bioinformation is one issue, but what is the value of this information in the criminal justice system if police, legal professionals, witnesses and juries don't understand it?

We need to improve the way that statistical evidence is presented to juries. If statistical evaluations are too complex for a jury to comprehend, alternatives must be found. The Crown Prosecution Service (CPS) has continued to shy away from dealing with this issue.

Given the potential for cross-contamination of evidence, a DNA match can never be taken as sufficient to prove guilt in the absence of other evidence. Corroboration of evidence is already a requirement in Scottish law.

The House of Commons Science & Technology Select Committee's 2005 report on forensic science recommended that a Scientific Review Committee should be established within the governments Criminal Cases Review Commission. This would provide ongoing scientific scrutiny of expert evidence.

Greater debate

DNA profiling is becoming a central part of police investigations. With the growth of the National DNA Database, profiling will increasingly be used to identify suspects rather than simply linking known suspects to a crime.

Developments in the chemical and analytical sciences are likely to make DNA profiling even more important to police investigations. Advances in analytical techniques applied to forensic methods will
include mobile laboratories for DNA analysis at the crime scene and the automation of laboratory analytical processes to enable higher throughput of samples.

To date, there has been minimal parliamentary and public debate about the National DNA Database and its use. The database is constantly growing, but how supportive is the public in this endeavour and what rights should people have to keep such information private? The RSC would like to see a full public debate.


Nuffield Council on Bioethics

Nuffield Council on Bioethics: The forensic use of bioinformation

30 January 2007

The Royal Society of Chemistry and the Bioscience Federation responds to Nuffield Council on Bioethics.

Contact and Further Information

Dr Ellen Friel
Programme Manager, Life Sciences
Royal Society of Chemistry, Thomas Graham House, Science Park, Milton Road, Cambridge CB4 0WF
Tel: +44 (0) 1223 432440