Forensic DNA expert Ate Kloosterman has been a researcher with the Nederlands Forensisch Intituut (NFI) [the Netherlands Forensic Institute] for years and is the expert in the area of DNA profiling. Since recently he has, as a professor by special appointment at the Institute for Biodiversity and Ecosystem Dynamics, been teaching University of Amsterdam Master's students the tricks of his exciting trade.
After graduating in Chemistry from Utrecht University, Kloosterman was employed in 1976 as a researcher at the central laboratory of the Amsterdam Blood Transfusion Department (CLB). Two and a half years later he was asked to apply for a post at the NFI, known at the time as the Gerechtelijk Laboratorium [Forensic Laboratory]. ‘A permanent job in an area I had always found fascinating', says Kloosterman. ‘In those days we were not yet able to conduct DNA research, so blood group serology was the subject.'
Kloosterman assisted in setting up a research team specialising in the examination of bodily fluids. Blood stains, saliva and sperm stains contain key information for tracing donors. One frequently used analysis involves blood groups. The analysis is based on the presence or absence of antigens; specific molecules attached to the surface of red blood cells. These antigens may also be present on cells from other bodily fluids. This means that blood groups can also be determined on the basis of sperm, saliva, nasal mucus and sweat.
‘However, blood groups by themselves did not yield a great deal of information', according to Kloosterman. ‘They only made it possible to exclude people. Finding a blood group A stain at the crime scene while the suspect had group B enabled you to exclude the suspect. However, if both the stain and the suspect belonged to group A, then all you had to go on was the knowledge that forty per cent of the population belonged to that group; so that didn't get you very far.'
Kloosterman sought other ways of classifying blood. He examined genetically polymorphous enzymes; large protein molecules in red blood cells which look different for different groups of people. ‘By examining the blood group as well as approximately ten enzyme systems, we were able to link traces to specific individuals with a high degree of probability.' Kloosterman explains that a rarity value of less than one in tens of thousands of people could be achieved with these systems, which meant that only one in tens of thousands of people had the exact combination of genetic factors observed in the trace and in the suspect's reference blood sample. ‘So we did very good work in those days as well', Kloosterman continues. ‘The only disadvantage was that the system worked much less well for saliva and sperm traces.'
In 1984 it was discovered that, although human DNA is largely identical for all human beings, there are certain elements by which individuals differ. A number of these elements - called markers - together form a profile as unique as a finger print. For this reason the technique is sometimes referred to as genetic finger printing. ‘I was overjoyed when DNA appeared on the scene. We realised it was bound to be a gold mine for forensic research.' And yet, up to that time Kloosterman had been wary of using DNA. ‘We had difficulty enough isolating protein molecules in dried stains because many structures do not survive drying in. And because DNA is such an incredibly complex substance we thought it would never be stable enough to be proof against drying in or senescence. But when it turned out to be stable after all we realised that our world would change forever.'
Kloosterman made an enthusiastic start setting up DNA research in the Netherlands. ‘We had to make a dash for it to ensure we mastered the technology ourselves. Fortunately we could hire somebody who had gained experience in an American laboratory in constructing DNA profiles. And we actually managed to do it. In very little time we were ready for DNA finger printing.' However, Kloosterman did not yet dare to use the technology in criminal trials. ‘We didn't have enough experience, and the criminal offences involved were very serious.'
One of the first Dutch trials in which DNA examination was used involved a series of rapes in Amsterdam. One of the suspects could not be excluded on the basis of his blood group. Together with a sample of his blood the trace material was sent to a laboratory in Britain for DNA examination. It was established that the victims had been raped by the same man, but not by the suspect. ‘So acquittal as a result of DNA examination was really possible. That resulted in a lot of publicity. It convinced everybody in the country that we had to set to work as soon as possible to be able to conduct DNA examinations ourselves. Funding for people and equipment was made available and within a short period of time we were able to do the examinations ourselves.'
One of Kloosterman's specialities is contact traces. Kloosterman leans his bare underarm on the table to illustrate. ‘By sitting like this everybody leaves some cell material. The trouble with such contact traces is that they contain incredibly small amounts of DNA. And yet, they are there. Such cells are also left in contacts with other people. For example, a strangler will leave cells on the victim's body. It is therefore of vital importance for such traces to be sampled and analysed.' The NFI was quick to realise the potential of these kinds of traces and set up a scientific research project. ‘We managed relatively quickly to develop a robust and reliable method for this type of examination. This method has been implemented as standard.'
DNA profiles of suspects and convicts are recorded in a large data bank. In Britain an enormous data bank has been developed over twenty years. Recently, however, that country was rapped over the knuckles by the European Court of Justice for having failed to remove profiles of non-convicted suspects from the data bank. ‘We're not talking about a few profiles, but about hundreds of thousands', according to Kloosterman. ‘Even without those profiles, however, the British data bank is much larger than ours. In that country people who urinate in public or fail to pay for a bar of chocolate at the supermarket are honoured with a place in the data bank.' Kloosterman is hesitant when asked to pronounce on the potential for a similarly strict policy in the Netherlands. ‘Of course it's a purely political decision, and I wouldn't want to express an opinion on it, but technically speaking it's perfectly possible. I should perhaps mention in this connection that several serious crimes were solved in Britain as a result of data bank hits being registered for people whose DNA profiles had been included for relatively minor offences.'
Since 2005, Kloosterman has taught the subject ‘Chain of Evidence' as part of the two-year Master's programme in Forensic Science. ‘In the first part of the course students become familiar with the basic forensic examination skills. For example, how to make sure that the evidence is examined in an uninterrupted chain. In the second part they put into practice what they have learned by being given a number of mock cases. We think up a story, for example involving a murder, and construct pieces of documentary evidence, collectively referred to as ‘the evidence'. The students then try to discover traces. Finding a great many of them and being unable to examine everything, they are forced to make a well-founded selection. On the basis of their selection they construct a DNA profile, and write a forensic report. Eventually they are required to defend their forensic examination in a role play court case with a real judge and a real public prosecutor. The students always look very much forward to that, but dread it at the same time. In any case, those sessions are always very interesting.'
The relatively new Forensic Science Master's programme is popular, attracting around 35 students each year. ‘Up until recently, most of the students had biomedical backgrounds. But now I perceive a slight shift, which is interesting because our profession is nothing if not multidisciplinary.' After graduating, the forensic students end up in various places: forensic police departments, foreign laboratories, the Netherlands Organisation for Applied Scientific Research (TNO), but also the NFI. ‘The job opportunities are somewhat limited. We don't need hundreds of new forensic examiners every year, but I am pleased there are a now fair number of people at the NFI who graduated in Forensic Science.'
Although Kloosterman himself did not opt for forensic science directly during his years of study he is very enthusiastic about his work. ‘I really like doing research which demonstrably has direct social relevance. I more or less rolled into this by accident via the blood transfusion service, but was hooked on the job from the beginning. Every day I thought to myself what a tremendous amount could still be done in this area. And I still do. In fact, I have enough questions for years of research.'