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Have the police hijacked our DNA?
EDITORIAL
THE LANCET Volume 362, Number 9388
Have the police hijacked our DNA? When Kevin Morris, chairman of the UK Police Superintendents Association, said last week that every person in the UK should have their DNA profile entered onto the National DNA database, he may have unwittingly begun the public debate that governments and police have so far avoided. If so, this debate has happened far too late. The UK is advancing towards a national database—already 2 million records are held (out of a population of around 60 million people). The US national database, CORDIS, currently holds just over 1 400 000 samples (from a population of 250 million people). These DNA databases contain computerised representations of so-called DNA fingerprints—a number of short tandem DNA repeats generated by PCR and analysed by computer to produce a profile. Because of the heterogeneity of the repeats, profiles are very unlikely to be the same between any two individuals. Hence the enormous power of DNA to identify individuals. But Alec Jeffreys, who first described a method for analysing these repeats, has warned that “DNA’s power is both its strength and its Achilles’ heel”. Some uses of forensic DNA technology are uncontroversial. DNA profiling has a sadly increasing role in identifying victims of mass disasters and communal graves. But the use of DNA evidence in criminal cases, in particular the use of so-called cold hits to identify perpetrators, is worrisome. This technique involves attempting to match a DNA profile obtained from a crime scene against a DNA database. Police forces across the world claim that this technique has allowed them to solve many cases, some years old. In New York City police are going one step further. To prevent sex-offenders from using the statute of limitations to escape prosecution, where no match can be made to a person, the DNA itself will be charged with the offence. But this approach ignores the fundamental reason for a statute of limitations—in very old cases it is hard for defendants to defend themselves properly. It is strange that on this scientific issue, unlike many others, the general public seems willing to believe all it is told by governments and police. In this context, DNA is simply physical evidence, albeit very sensitive evidence, that can be mishandled and misinterpreted. A recent textbook, Forensic Medicine: Clinical and Pathological Aspects (edited by Jason Payne James,
Anthony Busuttil, and William Smock, Greenwich Medical Media Limited, 2003) has a chapter on the statistics necessary to understand forensic evidence. For DNA, the message is simple: if a stain from a crime scene comes from the perpetrator, then a potential suspect’s DNA must match that of the stain. Despite dizzying numbers often quoted in courts (eg, 30 million to one), the converse is not true; if a person’s DNA matches that of the stain it does not prove they are the criminal. How does this follow? First, a DNA profile can be generated from very few cells that can be left by innocent means—the amount left on a drinking glass or a door handle. Second, although the number of DNA repeats used to compare profiles means it is very unlikely that any two individuals will have the same profile, it is not impossible. Third, at least in the USA, the standard of work in many laboratories that handle DNA evidence is not consistent; despite several cases where laboratories mishandled DNA evidence only three states, New York, Oklahoma, and Texas require accreditation to specified standards. Of course, DNA is not just physical evidence. Much more information can be derived from the DNA that the profile is generated from. Police scientists are already investigating the correlation of DNA markers with physical characteristics. Central to these issues is whose profiles are on these national databases. The UK database comprises (in perpetuity) not only convicted criminals, but also anyone charged, and even simply arrested, for a recordable offence. Hence the database is skewed towards those that the police believe are likely to have committed a crime. The publicity stunts by members of the government in having their DNA taken are simply a distraction from the discriminatory nature of the current database; the white middle-classes are not those whose profiles are being preferentially accumulated. Perhaps we should make a database of all men—according to the UK Home Office statistics for 2001, in 80% of violent incidents the perpetrators were male. This suggestion might seem ludicrous, but so far no-one, even civil liberties groups who complain that the government wants to make a universal database, has devised a more rational alternative. The Lancet
THE LANCET • Vol 362 • September 20, 2003 • www.thelancet.com
For personal use. Only reproduce with permission from The Lancet.
927
THE LANCET Volume 362, Number 9388
Have the police hijacked our DNA? When Kevin Morris, chairman of the UK Police Superintendents Association, said last week that every person in the UK should have their DNA profile entered onto the National DNA database, he may have unwittingly begun the public debate that governments and police have so far avoided. If so, this debate has happened far too late. The UK is advancing towards a national database—already 2 million records are held (out of a population of around 60 million people). The US national database, CORDIS, currently holds just over 1 400 000 samples (from a population of 250 million people). These DNA databases contain computerised representations of so-called DNA fingerprints—a number of short tandem DNA repeats generated by PCR and analysed by computer to produce a profile. Because of the heterogeneity of the repeats, profiles are very unlikely to be the same between any two individuals. Hence the enormous power of DNA to identify individuals. But Alec Jeffreys, who first described a method for analysing these repeats, has warned that “DNA’s power is both its strength and its Achilles’ heel”. Some uses of forensic DNA technology are uncontroversial. DNA profiling has a sadly increasing role in identifying victims of mass disasters and communal graves. But the use of DNA evidence in criminal cases, in particular the use of so-called cold hits to identify perpetrators, is worrisome. This technique involves attempting to match a DNA profile obtained from a crime scene against a DNA database. Police forces across the world claim that this technique has allowed them to solve many cases, some years old. In New York City police are going one step further. To prevent sex-offenders from using the statute of limitations to escape prosecution, where no match can be made to a person, the DNA itself will be charged with the offence. But this approach ignores the fundamental reason for a statute of limitations—in very old cases it is hard for defendants to defend themselves properly. It is strange that on this scientific issue, unlike many others, the general public seems willing to believe all it is told by governments and police. In this context, DNA is simply physical evidence, albeit very sensitive evidence, that can be mishandled and misinterpreted. A recent textbook, Forensic Medicine: Clinical and Pathological Aspects (edited by Jason Payne James,
Anthony Busuttil, and William Smock, Greenwich Medical Media Limited, 2003) has a chapter on the statistics necessary to understand forensic evidence. For DNA, the message is simple: if a stain from a crime scene comes from the perpetrator, then a potential suspect’s DNA must match that of the stain. Despite dizzying numbers often quoted in courts (eg, 30 million to one), the converse is not true; if a person’s DNA matches that of the stain it does not prove they are the criminal. How does this follow? First, a DNA profile can be generated from very few cells that can be left by innocent means—the amount left on a drinking glass or a door handle. Second, although the number of DNA repeats used to compare profiles means it is very unlikely that any two individuals will have the same profile, it is not impossible. Third, at least in the USA, the standard of work in many laboratories that handle DNA evidence is not consistent; despite several cases where laboratories mishandled DNA evidence only three states, New York, Oklahoma, and Texas require accreditation to specified standards. Of course, DNA is not just physical evidence. Much more information can be derived from the DNA that the profile is generated from. Police scientists are already investigating the correlation of DNA markers with physical characteristics. Central to these issues is whose profiles are on these national databases. The UK database comprises (in perpetuity) not only convicted criminals, but also anyone charged, and even simply arrested, for a recordable offence. Hence the database is skewed towards those that the police believe are likely to have committed a crime. The publicity stunts by members of the government in having their DNA taken are simply a distraction from the discriminatory nature of the current database; the white middle-classes are not those whose profiles are being preferentially accumulated. Perhaps we should make a database of all men—according to the UK Home Office statistics for 2001, in 80% of violent incidents the perpetrators were male. This suggestion might seem ludicrous, but so far no-one, even civil liberties groups who complain that the government wants to make a universal database, has devised a more rational alternative. The Lancet
THE LANCET • Vol 362 • September 20, 2003 • www.thelancet.com
For personal use. Only reproduce with permission from The Lancet.
927