What CSI Doesn’t Tell You – Part Two

In part one, we looked at some of the ways the hit show CSI: Crime Scene Investigation can be misleading about the realities of forensic science. In part two, we’re going to take a look at some of the realities of this fascinating branch of science.

DNA profiling is actually a relatively new form of forensic science – the first conviction using DNA evidence was that of the murderer Colin Pitchfork in 1987. When it was first discovered, DNA profiling was difficult and rare – a relatively large sample was needed, and was often destroyed in the process of testing so there were no opportunities for repeated testing. As technology has evolved, it has become possible to analyse smaller samples, meaning that more crimes can be solved with DNA.

DNA can be very powerful evidence – it is often sought in cold cases or in miscarriages of justice, and has been used to prove both guilt and innocence. Theoretically, the chance of a coincidental match is something like one in a billion.

However, it’s not always a definitive answer. In cases where the sample may contain DNA from several individuals, it is often a challenge to separate out the different contributors, and care must be taken with the samples to ensure that no contamination prejudices the evidence. In one extreme example, police spent several years chasing “the Phantom of Heilbronn”, a woman whose DNA appeared at 40 crime scenes in Austria, France and Germany between 1993 and 2009 – including six murder scenes. Eventually, it was discovered that the DNA belonged to a woman who worked in a factory producing cotton swabs – the same swabs that had been used to collect the evidence.

Fingerprint evidence is also commonly shown as a powerful piece of evidence in TV shows. First developed in the late nineteenth century, they were first successfully used to secure a conviction in 1902. Over the years, various different forms of classification have been used to study and categorise fingerprints. Generally, these systems are based on the number and position of identifiable features in the pattern – whorls, loops and arches.

Today, there are a number of official fingerprint databases held by police forces to allow for efficient comparison when a fingerprint is found at a crime scene. However, unlike on TV, they are not simply compared by a computer; the database narrows down the options, and the comparisons are usually made visually by the forensic analyst.

Again, there is room for doubt – criminals are well aware of the use of fingerprint evidence, so finding a print that is clear enough for a definitive match is rare. It is far more often the case that the analyst is working with a partial print, and must assess the likelihood of it being a match to the suspect’s print.

These are just two of the techniques used every day by real-world crime scene investigators, and for those with the right aptitude and attitude it can be an incredibly rewarding area of work. If you are teaching a budding analyst, then you can check out our wide range of science equipment to help encourage and inspire them. For more information, contact us on 01366 385777.