Today, although most crimes continue to be solved through confessions and eyewitness accounts, scientific evidence is increasingly being used to establish the truth. Advances in technology have helped DNA analysis to become an established part of criminal justice procedure.

Despite early controversies, and challenges by defense lawyers, the admissibility of DNA test results in the courtroom has become routine in most of the countries in the world. During the past two decades, identification based on the differences that exist in the DNA molecule has indeed become an invaluable instrument in the search for justice. The prosecutors never had such a powerful tool at their disposal, both to convict the guilty and exonerate the innocent.

DNA, or Deoxyribonucleic acid, is the chemical storehouse of an individual's genetic material. It is a tiny thread-like molecule that contains all the information required for the life process. It is the hereditary blueprint passed on to us by our parents. It governs the inheritance of all the characteristics of an individual, such as, eye colour, hair colour, stature, bone density, likes, dislikes etc.

It is a component of virtually all the cells in the human body. A person's DNA is the same in each cell, and does not change throughout his lifetime. Any bodily substance, like blood, saliva, semen, hair, tooth, bone, tissue etc., therefore, can serve as a potential source of DNA.

By using modern molecular biological techniques, it is now possible to generate a DNA profile from any one of those subtances, where the possibility of finding two individuals with the same DNA profile is in the order of 1 in a trillion.

DNA analysis can link suspects to violent crimes like rape or murder by comparing DNA evidence recovered from the crime scene, or victim, with the DNA sample taken from the suspect. By means of DNA analysis, it is also possible to resolve disputes arising over paternity or maternity, immigration disputes, identification of missing children, mutilated dead bodies, disaster victims, and exchange of babies in hospital wards.

DNA technology was first used in criminal justice in 1987 in the UK, to convict a criminal who allegedly raped and murdered two teenage schoolgirls. Bangladesh is not far behind in accepting this technology, as the Ministry of Women and Children Affairs has established a national forensic DNA profiling laboratory at Dhaka Medical College, with the financial and technical assistance of the Denmark government.

This laboratory started providing its service to various law enforcing agencies from January, 2006. Though the laboratory has had a good start, it has a long way to go to realize the full advantage of the power of DNA technology to solve crimes and protect the innocent.

The first important step that has to be taken is the creation of a national DNA database. The question is, what is a DNA database? And how does it in help solving crimes?

A DNA database means an electronic database of DNA profiles. The database, however, is not simply a collection of DNA profiles, but a composite database where DNA profiles are organized in different indexes, with the capability of electronically searching, retrieving and comparing, thereby linking crimes to each other and to the convicted offenders. Ideally, a DNA database should include DNA profiles under the following indexes:

• Crime scene index
• Convicted offender's index
• Missing person's index

Crime scene index
The crime scene index contains DNA profiles from biological evidence (blood, blood stain, semen, saliva etc.) obtained at the scene of the crime. This type of DNA index can link crime scenes together, possibly identifying serial offenders. This database is equally useful once a perpetrator is identified.

Convicted offender index
The convicted offender index contains DNA profiles of individuals convicted of violent crimes (e.g murder or rape). Many countries, like the UK, Netherlands and Australia even include DNA profiles of individuals convicted of recordable offenses.

The criteria, of course, differ from country to country, and require legislation prior to implementation of such a database. The existence of this kind of database enables law-enforcing agencies to identify possible suspects, and link suspects to unsolved crimes or cases where no suspect was available. Matches made between crime scene and convicted offender indexes provide investigators with the identity of the perpetrator.

Missing person's index
This portion of the database would contain DNA profiles from unidentified dead bodies, body parts or body remains. This database would provide greatest benefit when DNA profiles from immediate relatives could be used to reconstruct DNA profiles for comparison, and to confirm the identity of a disaster victim or a missing person.

International scenario
The world's first DNA database was established by Forensic Science Service (FSS), UK in 1985. The British database holds profiles of around 2.3 million offenders and 2,32,000 crime scene samples. This database is currently achieving 1400 matches between crime-scene samples and suspects every week.

Another such DNA database, called Codis (Combined DNA Index System), is maintained by the FBI, United States. The FBI's databank has profiles of about 6,00,000 convicted offenders, and 26,000 crime-scene samples. Countries having such a DNA database can link up with the international database through Interpol (International Criminal Police Organization).

Participating countries will be able to add profiles from their national or regional databases, and compare their profiles with those supplied by the participating Interpol member states. The advantage in participating in this type of data exchange program is that it helps investigators to identify a suspect who has moved to another country after committing a crime, and has eventually been arrested.

The potential benefit of creating a national DNA database is obvious. Though the initial cost of establishing a database is high, experience from other countries shows that it can cut down the cost of a trial by about one-fifth, reduce the man hours in the judiciary, help in linking suspects to unsolved cases, exonerate the innocent, solve more crimes, and prevent crime.

Dr. Sharif Akhteruzzaman is Professor, Department of Biochemistry and Molecular Biology, University of Dhaka, and Head of National Forensic DNA Profiling Laboratory, Dhaka Medical College.