What are the advantages of the use of DNA in criminal cases?

What is DNA?

Deoxyribonucleic acid – or DNA as it is more commonly known – is the main component of chromosomes and is the material that carries genetic information in all life forms.

DNA and the criminal justice system

DNA has revolutionised the field of criminology and hugely improved the functioning of the criminal justice system. The main ways DNA testing can be used to great effect in the criminal justice system are to:

  • solve crimes;
  • identify victims of crime;
  • link crimes.

Solving crimes

Since the advent of DNA profiling, DNA has been used as evidence and has become a powerful tool in the field of the criminal law. Often the DNA of an individual may be found on the body of their victim or at the scene of the crime and can help pinpoint that individual as the perpetrator.

Since an individual’s DNA is the same in all areas of their body, it cannot be altered or changed in any way, meaning it is effectively a form of evidence which is resistant to any form of tampering.

No DNA is the same between two individual people (apart from identical twins), which means the evidence can be relied upon as an accurate way to direct or to conclude criminal cases.

DNA testing at a crime scene will often enable investigators to move the case in the right direction and remove potential suspects from the investigation. This enables the police to concentrate their manpower directly on the case, rather than wasting time interviewing potential suspects.

Identifying victims of crime

Another important function of DNA in criminal cases is enabling the victims of crime to be identified. In some cases, where the condition of the body when discovered has left the victim unidentifiable, hair and many other parts of the body can provide viable DNA evidence. This can be analysed and profiled to identify the victim of the crime.

Linking crimes

If the same DNA is found at two different crime scenes, it can be used to link together the crimes. This allows criminal investigators to determine if a serial criminal is at large or to establish if the victims knew one another.

Possible challenges to DNA evidence

DNA evidence is not always conclusive. Samples can degrade with age, or become contaminated depending on the environment in which they are found, transported or stored. Questions can also arise about the qualifications of the people doing the testing and those doing the analysis.

Law enforcement officers dealing with DNA samples need to ensure that all the correct protocols are followed when collecting the samples, transporting them, storing them and when carrying out the actual DNA testing.

The National DNA Database

DNA samples which have been obtained for analysis from a crime scene and from samples taken from individuals in police custody can be held in a national database called the National DNA Database.

The UK’s National DNA Database is the largest database of any country. Over the last few years, there has been a continued expansion of the DNA database – as of December 2016, there were more than five million DNA profiles being held on the database, which accounts for the majority of the population of known active offenders.

The Protection of Freedoms Act 2012 reformed the government’s stance on DNA and fingerprint retention so that only people convicted of an offence will have their fingerprint records and DNA profiles retained indefinitely.

Samples from people arrested but not charged, or charged but not convicted, can only be retained for three years (with a possible two-year extension if granted by a district judge) if the offence was a recordable qualifying offence (generally, an imprisonable offence). Samples from those arrested or charged with a minor offence cannon be retained (unless they have a previous conviction for a recordable offence, in which case they can be retained indefinitely).

What happens when police find a DNA match?

Upon receipt of a DNA match report from the National DNA Database, the police will proceed to arrest the suspect. However, charges cannot be brought upon a DNA profile match alone – there must always be appropriate supporting evidence.

What the process will be once the charges are brought depends upon the plea by the defendant:

  • If there is a clear indication of a guilty plea, following consultation with the Crown Prosecution Service (CPS) it may be possible to proceed without the need for any further investigative or forensic work being done.
  • If there is no indication of a guilty plea but the DNA evidence is not in issue, the CPS may decide to proceed on the basis of the National DNA Database match report.
  • If there is no indication of a guilty plea or in fact no plea at all and the DNA evidence is an issue in the case, then an abbreviated statement will be requested from the forensic science provider (FSP).
  • If there is an indication of a not guilty plea and the DNA evidence is an issue then a full evaluative statement and continuity evidence concerning the DNA findings must be supplied by the FSP.