Science is often in the witness box these days as we try to deliver justice in society by turning to forensic expertise. One of these experts is Dr Adrian MT Linacre of the Centre for Forensic Science at Strathclyde University, Glasgow, who is currently a visiting professor at Mahidol University.

Linacre, a good friend of Dr Pornthip Rojanasunand, the acting director of the Central Institute of Forensic Science, believes that justice will prevail if forensic experts at crime scenes are independent and impartial, since the scientific method of DNA profiling and matching is very accurate. In fact, the uniqueness of a particular DNA profile is one in a billion. However, accuracy can be seriously affected by human error.

According to Linacre, who graduated from Edinburgh and Sussex universities before joining Strathclyde in 1994, one of the most common human errors in DNA profiling and matching occurs when DNA samples of several persons at a crime scene are mixed together, resulting in inaccuracies.

Another problem is when biological samples show no results and investigators cannot collect additional evidence from the original crime scene.

Linacre believes the process of justice begins at the crime scene right after law enforcement officials are informed of the incident and ends in the courts. Along the way, laboratories and scientific evidence assist the process. If any link in this chain is weak, the end result might also be weak, he says.

Linacre has worked for prosecutors and the courts in Glasgow for the past eight years.

"I perform casework for the courts and have been authorised to give evidence by the Secretary of State for Scotland. I am also an assessor in the area of human contact traces for the Council for the Registration of Forensic Practitioners," he said.

Linacre's expertise lies in forensic biology, which includes body-fluid analysis, blood-pattern analysis and DNA profiling. On average he is involved in about 200 cases a year.

One of his most challenging cases was the murder of an elderly woman by strangulation with a stocking in 2002 and a similar crime about five years earlier.

Using cotton swabs, forensic scientists were able collect a very small amount of skin cells from the stockings for the lab to conduct DNA profiling. The results showed no perfect match with any of the suspects, and only a 50-per-cent match with one. Investigators then narrowed the list of suspects to the family group of the one with the 50 per cent match.

Linacre explained that a person's DNA profile consists of two halves, one from the biological father and the other from the biological mother. With this knowledge, investigators narrowed the list of suspects down to the four children of the original suspect whose DNA showed a 50-per-cent match. Eventually, the DNA profile of one of the sons was found to perfectly match the samples from the crime scenes.

In practice, the forensic scientist's work is finished once he or she hands over their findings to law enforcement officials. Linacre says he often doesn't know the motive of a crime until he reads the newspapers after the court delivers a verdict.

The British justice system ensures that different authorities are responsible for different parts of the legal process. For example, prosecutors are in charge of enlisting the help of forensic scientists and directing the work of the police, so it is not possible for the police to manipulate an investigation.

In Thailand, the separation between police and forensic experts is still not complete, resulting in a weakness in the process of justice.

With his expertise in forensic biology, Linacre has been invited to lecture at Mahidol University's post-graduate programme on forensic science for the past three years. In the UK, he is a course coordinator for a new degree in forensic biology and teaches both forensic and analytical chemistry.

Linacre, Pornthip and other Thai forensic experts last week took part in a seminar entitled "Science in the Witness Box", organised by the British Council at its Bangkok branch, to raise public awareness about the role of science in the justice process.

Nophakhun Limsamarnphun

nop1122@yahoo.com