DNA testing has three major applications for forensic studies:
identification of missing persons; identification of victims of
wars, accidents, and natural disasters; and crime investigation.
Annually, more than 20,000 forensic DNA tests are performed in
the UK. Two out of three of all criminal cases using DNA
evidence involve sexual assault, the rest are cases dealing with
burglary, murder, and other types of violent crime. During the
last 15 years, DNA trial analysis became an indispensable police tool in
fighting crime because it allows unambiguous identification of
the criminal by traces of biological material left at the crime
scene. It can also acquit innocent suspects based on DNA
evidence.
Criminal justice system now relies heavily on DNA-based
evidence. Since it was first used in the Enderby murder case
(1986), thousands of perpetrators has been convicted of various
crimes with the help of DNA evidence, and hundreds wrongfully
convicted people have been exonerated
The most common samples collected at the crime scene are blood,
semen, and saliva; virtually any biological material or objects
handled by a perpetrator can be now used for forensic DNA
testing. Clothing, furniture, and other items which may have
traces of DNA, are now routinely used for obtaining DNA
evidence. The technology is so sensitive that it allows
identification of a person by analysing DNA collected from a
fingerprint left on the surface of an object or from a single
hair left at a crime scene.
When a crime scene sample or a sample from a suspect is
analysed, a DNA profile is produced. A DNA profile is a
digitalised representation of an individual?s genotype with
respect to the DNA markers tested. In the UK, all crime scene
DNA profiles together with those of all suspects and arrestees
for any recordable offence are deposited into a National DNA
Database (NDNAD), which is the world?s first criminal DNA
database. As of 2004, the UK national DNA database held over two
and a half million DNA profiles collected from suspects and
convicted criminals which is estimated to be about 40% of UK
criminally active population as well as more than 200,000 crime
scene samples. UK Police use the NDNAD as an investigative tool
to help solving a wide range of crimes including murder, rape,
sexual assault, robbery, terrorism, burglary and arson and have
almost doubled their clearance rate for volume crimes such as
house burglary, and motor vehicle offences. As each new subject
sample profile is added to the database, it is checked against
all contained crime scene sample. When a new crime scene sample
profile is added, it is checked against DNA profiles of all
suspected individuals as well as against other crime scene
sample records. Since its inception in 1995, the NDNAD had
matched more than 200,000 crime scene samples to suspects and
more than 20,000 crime scene samples to other crime scenes.
Every week more than 300 crime scene samples are matched to the
suspect and convicted criminal?s database.
However, a DNA match between a suspect and a crime scene does
not automatically guarantee a conviction. DNA evidence is just
another piece of evidence, although very strong one, and on its
own is often not enough to convict someone of a particular
crime. DNA evidence must always be taken in conjunction with
other pieces of evidence and the weight of DNA evidence is
impossible to estimate without taking into account the
circumstances of the case. Even when a strong match between a
defendant and a crime scene sample is presented by the
prosecution, non-DNA evidence may be pointed to someone else as
the real perpetrator of the crime. This ?other? evidence can
decrease the weight of DNA evidence and increase the chances of
successful defence.
The discovery of DNA fingerprinting 20 years ago had
revolutionised the legal profession. Criminal and non-criminal
justice systems were handed a very powerful tool to solve crime
and resolve civil cases. Understanding how DNA testing can be
applied in legal profession will bring benefits to both lawyers
and their clients.
About the author:
Avi was awarded the prestigious Shell Live Wire Entrepreneur of
the Year award in 2004. Working closely with the charities and
various media outlets, Avi strives to increase public awareness
as to the benefits of DNA testing and the
continuing impact that technological advances will have on all
our lives.
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