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Law enforcement agencies in the US are starting to collect DNA samples
from convicted criminals. Their aim is to keep such ‘genetic profiles’ on
file, just as they keep fingerprints. Since June 1990, the state of Virginia
has collected blood samples from 33 000 people convicted of serious offences,
and 2000 more samples are added every month.

The purpose of these DNA banks is to help solve future crimes, says
Paul Ferrara, director of Virginia’s Division of Forensic Sciences. Police
will try to match DNA patterns from blood, hair or semen stains found at
the scene of a crime to DNA data on past offenders.

Thirteen states now have laws allowing police to collect samples of
DNA from convicts. Seven states are sharing their data as part of a pilot
programme organised by the FBI. Virginia, however, is far ahead of the other
states in developing its programme. Next month, Ferrara’s laboratory will
move to huge new premises designed for storage and analysis of genetic samples
and data.

At a meeting last week, sponsored by the National Institutes of Health,
Phillip Reilly of the Shriver Center for the Mentally Retarded, near Boston,
Massachusetts, said ‘we are experiencing an explosion in forensic data banks’.
Law enforcement agencies in the US already maintain larger collections of
genetic data than all academic and research institutions combined, and their
data banks are growing very rapidly. ‘What’s amazing is how much has happened
with so little attention,’ says Reilly.

Originally, forensic data banks of genetic information were set up specifically
to help solve rape cases. In these cases, DNA samples are frequently available
in semen residues and many rapists are repeat offenders. According to a
survey carried out by the US Department of Justice, half of all rapists
released from prison in 1983 were reconvicted of rape within three years.

Many states now allow much broader use of DNA databanks, usually covering
anyone convicted of a serious criminal offence. Iowa’s law allows police
to collect DNA samples from those convicted of minor offences as well. The
Pentagon, meanwhile, is looking into the possibility of collecting DNA samples
from all its soldiers and keeping them on file. This information could help
identify soldiers killed in combat.

At the NIH meeting, several lawyers and experts in ethics voiced concern
about uncontrolled growth in genetic data banks. They fear that police will
be tempted to collect genetic data from ever-widening groups of people.

False matches between DNA found at the crime scene and samples kept
on file could cast suspicion on innocent people. DNA patterns are not unique:
identical twins, for example, have exactly the same genetic material. In
addition, a ‘match’ between two samples of DNA often cannot be determined
with absolute precision.

According to Ferrara, a search of his data banks for a DNA sample that
matched one found at a crime scene would bring up any ‘near matches’, because
test results that differ slightly could still be from the same person’s
DNA. Police could then use this set of ‘near matches’ as a ‘list of suspects’,
he says. That list could include one, two or ten people, depending how closely
Ferrara required the two samples to match. The danger in this procedure,
according to participants in the NIH workshop, is that it could easily become
an exercise in ’rounding up the usual suspects’.