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“All Citizens are Equal before Law and are Entitled to Equal Protection of Law”-Article 27 of the Constitution of the People’s Republic of Bangladesh

Issue No: 252
August 26, 2006

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Investigating crimes: Importance of DNA analysis aspect

Barrister Omar Bin Harun Khan

A judge is not supposed to be a specialist in every branch of knowledge so as to form an 'expert opinion' upon whatever questions might crop up on whatever subject in the course of judicial proceedings handled by him from day to day. He is, therefore, empowered to take assistance from experts on a subject unfamiliar to his ken of comprehension. In Bangladesh the power of the court to take expert evidence stems form sections 45 to 50 of the Evidence Act. Forensic Medicine brings the medical practitioners into contact with the law, as this are such a matter, which requires expert opinion. medical Jurisprudence, Forensic Medicine and Legal Medicine are considered synonymous terms and is used to denote the aspect of medical science, which is applied to the administration of justice. In addition to assist the judge by providing expert opinion in the court, the forensic medicine science plays a vital role in the investigation of crimes in different ways: Identification of victim or defendant, postmortem examination, examination of blood, semen, hair, bones, saliva, urine etc., death, injury, sexual matters, insanity, toxicology and so on. In this article, I will focus on the most modern tool of medical science in the investigation of crimes: DNA analysis.

The investigation of crime to find out the criminal and bring him to justice is not at all an easy task. The criminal investigators achieve this in a number of ways: by examining eyewitnesses' accounts and physical evidence recovered from the scene of crime. Among the physical evidence, DNA evidence has possibly the highest probative value, on par the finger print evidence, in identification of an individual and is one of the most modern ways to do it.

One of the most fundamental concepts of forensic science is “the dust and debris that cover our clothing and bodies are the mute witness, sure and faithful, of all our movements and all our encounters.” This means that when a person comes into contact with another person or substance he or she is bound to leave his/her physical presence by leaving some biological evidence.

The objective of forensic DNA analysis is simple: identification of the source of biological evidence collected from the scene of crime or any other related place and thereby to identify the perpetrator. The use of DNA for human identification purposes in the early 1980s has revolutionised forensic science and has thereby given the forensic science a new dimension. In the advanced legal systems, like that of the US, the UK and the most other EU countries, the criminal justice system now heavily rely on DNA-based evidence. In those countries thousands of perpetrators have been convicted of their crimes with the help of DNA evidence, and hundreds of wrongfully convicted persons have been exonerated. Thus DNA analysis has become an indispensable police tool, as it allows unambiguous identification of the criminal by tracing the biological matters left at the crime scenes. In modern times there is no scope to underestimate the importance of this silent but faithful witness in combating crime.

The probative value of DNA evidence in court is very high. If a match between the crime scene and the defendant is obtained, it may be of sufficient strength to narrow down the potential perpetrators to a small group or even to a single individual!

Before the advent of DNA, biological evidence was analysed by serological methods, which were based on examination of blood groups and various protein systems. DNA testing, within five years of introduction, completely replaced its predecessors. Now, a DNA analysis is a routine tool of police investigation with police forces world wide heavily relying on forensic DNA testing. In parallel with developing DNA testing technology, national criminal DNA databases have appeared in various countries. At the moment the USA, the UK and the most other European countries have DNA databases used by law enforcement agencies to combat crime.

The current forensic methodology used for DNA analysis produces only DNA profile of the biological stain recovered from the scene and allows determination of the gender of the contributor. In addition, it is also possible to tell whether one or more individuals have left biological material at the scene. The most recent development in the forensic science in terms of DNA analysis now enables the identification of ethnic origin of the person by examining the DNA, which has already been proved to be very effective in multiracial societies like the USA. This analysis allows telling whether the donor is of mixed origin and even estimating the proportion of ancestors from each ethic group. It is also possible to identify the heir and skin colours and even the colour of the eyeball of the donor. Some aspects of DNA changes with the person's age and basing on this concept, the scientist have invented ways to specify the age group of the donor, which is extremely crucial in correctly identifying the suspect.

The following points may help to answer why the DNA-based evidence has the highest degree of probative value in the courts and for the criminal investigators:

1. High Discrimination Power: Every person's DNA is unique. Current forensic DNA typing systems allow achieving discrimination power of 1 in several billions ensuring that every DNA profile obtained is virtually unique.

2. DNA profile is constant and does not change over time: Many other biometrical parameters used for human identification, such as Iris pigmentation, change during the person's life, but DNA profile does not. It is also impossible to replace one's DNA with someone else's.

3. Different types of cells have identical DNA profile: DNA profile obtained from different sources of the same individual have identical pattern regardless of the biological origin. A DNA profile from a seminal stain from one crime scene can be compared to that of a droplet of blood recovered from a different scene and if the same individual deposited the semen and blood identical DNA result will be obtained.

4. DNA is more stable than other biological evidences: Reliable data can be produced from very old and decayed biological samples. High molecular integrity of DNA allows forensic scientists to analyse long buried samples as well as samples which were subjected to high temperatures and chemical treatment. Even when the biological samples are severely degraded DNA evidence can be produced using modern forensic approaches. I have seen a documentary where the victim of a fire was identified by DNA analysis of the root inside his teeth as his whole body was almost converted into ash by the fire.

5. DNA evidence is inherited: Family members have similar DNA profile. Using sophisticated data analysis tools it is possible to identify a culprit with reasonable confidence by analysing DNA of his close relatives.

6. It is possible to generate millions of exact copies of DNA by specific enzymatic reactions which allow obtaining generic information from exceedingly small amounts of biological materiel: Modern day technology is so advanced that a single hair, skin flake or small droplet of sweat left at a crime scene is often sufficient to obtain a full DNA profile which can be used to identify the perpetrator of crime.

With the development of new technologies and understanding more about the function of human genes the scope of parameters about an individual which can be obtained by DNA-analysis will only expand. No other type of evidence is capable of producing so much information about the individual.

Despite the above-mentioned surprising features of the DNA analysis, it is very regrettable that far from establishing DNA databases and using DNA analysis as a tool in the criminal investigation, it has remained almost unknown to most of the criminal investigators in Bangladesh and is still considered as an alien concept by many lawyers and courts of our country. In this scientific age, it is very surprising that we are not even too familiar with the finger print evidence. There are uncountable number of incidents where the blood tests of the blood found at the crime scenes could not be carried out!

Of course, I agree with the critics that DNA analysis is very expensive and being a country having vulnerable economy it will be a huge burden on the public fund to establish a DNA-database and widely use DNA analysis in the investigation of crime. What I do believe is that the DNA analysis will save huge cost that now occurs in the other ancient methods of investigation; it will also save time and thereby money. Most importantly, it will bring the highest level of accuracy in the investigation of crime and hence the people will have faith in the Criminal Justice System again, which cannot be compromised with anything for any reason.

Some people may still feel that considering the prevailing investigative processes in our country, it is very much premature even to talk about DNA analysis. But at the same time we cannot also sit idle and do nothing for the improvement of the system of investigation of crime. If we start to realise the importance of DNA-analysis and start to talk about it, only then we may see some ray of light for the well-desired reform of the criminal investigation process.

The author is a practicing Barrister.


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