The science behind forensics

"Forensic science is just recent archaeology", says Allan Jamieson, Director of the Forensic Institute, Glasgow, as he explains how the same science can solve recent crimes and shed light on the past.

By: Professor Allan Jamieson (The Forensic Institute)

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Scientist with petri dish Copyrighted image Copyright: BBC

You may have the impression from TV programmes like Waking the Dead, Silent Witness, CSI (Crime Scene Investigation), and other such detective stories, that forensic science can unlock the story behind every crime. “Just the facts”, the policeman may ask. Facts are what science is all about. Isn’t it?

Actually the phrase "forensic science" has become confused for many. Forensic science is really just science used in court. But for many this term has become a shorthand for a whole host of tools and techniques; usually used to mean analytic or careful. Forensic science is both of those, but it is much more; and other sciences are also analytic and careful!

Semantics aside, this science can offer a fascinating way of examining the past. I frequently comment that forensic science is just recent archaeology. Many of the techniques used by scientists to unravel crimes today can be used to unravel stories of the past, even though no crime is involved.

Today and in the past, the first priority has been to establish whether there has been a crime at all. In Sir Arthur Conan Doyle’s book The Hound of The Baskervilles, Sherlock Holmes remarks “There are two questions waiting for us at the outset. The one is whether any crime has been committed at all; the second is, what is the crime and how was it committed?”

A great example of this kind of investigation is the death of Otzi; "The Ice Man". Otzi is the name given to the body of a man believed to have died over 5,000 years ago. He was discovered high in the Otzal Alps in 1991 in an area that had been frozen for centuries. Of course no-one is out to jail Otzi’s killer, if indeed he was killed, but the findings on and around his body have created intense speculation about how he died. Scientists are of course curious creatures and here is a curiosity.

Not only is Otzi’s death the subject of investigation, but some people think that there is a curse that has killed some of the investigators. Science is a very powerful method for sorting out such tangles. Many of them have been applied to the case of Otzi.

Palynology is the study of pollen. Not immediately obvious as a forensic science, but some plants live in very limited geographical areas, or produce pollen at very specific times. Palynologists reckon that the pollen of the hop hornbeam tree found in Otzi’s stomach means that he died in early spring or summer, and was probably at low altitude at most a day before he died.

Like all crime scenes, the scientist here is faced with trying to discover how the scene came to be the way it was discovered. This is the evidence and you must use that evidence to create a story; not the other way around. In modern crime terms; you don’t find a suspect and then try to fit the evidence around that suspect. A scientist tries to find evidence against any story, and the more that they look and find that the story stands up, the more they are inclined to believe it. But the evidence can fit many stories. The job of the scientist is to devise tests that can disprove or prove some of these stories.

Otzi may have died peacefully, been attacked by one or more people, or animals, or had a tragic accident. Some pieces of evidence fit one or more of these stories better than others. As in real life crime investigation, we will never be absolutely sure of the truth.

Examination of ‘the scene’ where Otzi lay, discovered some weapons, tools, and other bits and pieces.

Image of fingerprints Copyrighted image Copyright: The Forensic Institute Alongside fingerprints, DNA is of course, now the technique that most people think of when they think of forensic science. Yet DNA fingerprinting, as the original technique was called, was first used in court in 1988. Current forensic DNA technology, now called DNA profiling, can detect less than 100 picograms of DNA. That is 0.0000000001 grams of DNA. One single cell’s DNA, and you have about 100,000,000,000,000 cells in your body, can be detected.There’s not much chance that you won’t leave some trace at a scene!

DNA analysis of these and his clothes apparently revealed the DNA of at least four individuals. Some claim that this may show that he was attacked by three people, and the finding of blood on his cloak is thought to suggest that he carried someone on his back.

However, there is nothing to suggest that all of the blood got there during the same incident. Some of these stains could have been made weeks or months before he died. DNA from several animals was found on his weapons. Did this prove that was what he hunted? How else could the DNA have got onto the spears?

You can see how the same observation can be "consistent with" different stories. It is for that reason that the phrase, beloved of crime writers, is not very useful in real crime investigation. It merely means that the story being offered is one of the possibilities. The real job is to evaluate which of the possibilities is the best fit to all of the observations, not just those that fit what you think or wish.

X-rays are a recent development in historical terms and can be used by modern investigators to look at injuries to bones. Even breaks or fractures suffered years before can often be seen by radiographers. They can also sometimes identify victims of accidents or homicide, or sometimes match damage caused by surgery or extraction of teeth to medical records of victims.

In these instances radiography is used by osteologists (who study bones), and odontologists (who study teeth). Some forensic odontologists also claim to be able to identify the person who made a bite mark. Bite marks are sometimes found on the body of a victim of some kind of abuse, or even in items found at crime scenes such as cheese sandwiches or apples. In Otzi’s case, the findings were a bit more mundane. An arrowhead and part of the shaft were found embedded in his shoulder. This may be evidence of an attack, or maybe a hunting accident? These techniques have been around for a few years now, but some fairly modern scientific analyses used nowadays in forensic science have provided further clues about Otzi.

Image of substances being tested. Copyrighted image Copyright: The Forensic Institute The elements that are all around us, such as oxygen, nitrogen, carbon, and iron, are present in subtly different forms. These forms all behave exactly the same in their reactions with other chemicals as they form new ones such as carbon dioxide, water, and indeed all the chemicals that make you. However, a technique called isotopic analysis can tell the different forms apart. It’s called isotopic analysis because the different forms are called isotopes (the prefix ‘iso’ means ‘the same’; e.g. isobars, isotherms, isotonic). If you really must know, the difference between the forms is the number of neutrons in the nucleus of the atoms of the element. That may come in useful in your next pub quiz – maybe it’ll be a half a million pound question one day.

What makes them interesting is that the different isotopes are present in different ratios at different times and different places. The technique of radiocarbon dating uses the ratios of the isotopes of carbon to date fossils to the nearest few thousand years – so it’s not very accurate as a watch. Isotopic analysis of Otzi’s tooth enamel, and comparisons with samples from surrounding areas, showed that he had spent his childhood in the area in which he was found (the Eisack Valley in the South Tyrol, Italy) but that he spent his adulthood in Lower Vinschgau, also in the Tyrol.

Forensic isotopic analysis is now being applied to such things as adhesives, packaging materials, drugs, bullets, and even safety matches.

In attempting to sort out the good stories from the bad, it is not always obvious which evidence to believe. Different types of evidence can appear to contradict each other; Otzi’s arrows are claimed as evidence that he spent his time hunting at high altitude whereas the geological isotopic evidence suggests otherwise. There is no magic formula for working all of this out. The best that the scientists can do is give possible stories and some estimate of how confident they are in those stories. There is one exception; exclusion. If, for example, your DNA or fingerprint does not match the DNA of the perpetrator found at the crime scene then we are sure that you are not amongst the suspects.

A chemical test kit Copyrighted image Copyright: BBC Otzi died a long time ago – around 3,000BC. Forensic science has made contributions to more recent cases of some historical interest. Some have claimed scientific support for a new theory of who killed Rasputin. Apparently, from photographs of the wounds and ‘new forensic techniques’, it is thought that he was killed by three different guns. Like so many crime investigations, this one is compromised by the lack of clear documentation and recovery of evidence at the time. The recovery of the bullets, and possibly gunshot residue, would have provided an unequivocal answer to the question of the number of firearms. The ‘evidence’ has generated heated, if not informed, debate.

Science has helped, and continues to help, the historian. Assisting in answering questions about who, what, how, when, and where, perhaps leaving to the historian the vexed question of why? Geology, mathematics, physics, chemistry, biology, medicine, and the rest, combine to provide a powerful arsenal of today’s expertise to provide answers to our past.

For the future, there is much that remains to be discovered, not only in the development of new techniques in the physical and biological analysis of old material, but in the seemingly unending lists of new finds of tombs, artefacts, and samples created by history and now, hopefully, understood because of our scientific curiosity today. Forensic or not, it is fascinating science that takes us to different times and places.

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