Traces

by Patricia Wiltshire

  Look back out of the window. Now what do you see? If I have done my job correctly, perhaps what you once thought of as small and compact has become something vast and unknown. Your garden, even the tiniest garden, holds so much more information than you can possibly assimilate.

  From the vantage point of a tiny pollen grain, even the smallest garden is a vast landscape of different terrains – all interconnected as ecosystems are; all having a bearing on one another, but all with unique, identifiable characteristics as well. And if a garden is as vast as that, how much bigger is a field? How much wilder and more complex is a hedgerow, a moorland, a woodland? You might think you could get lost, and in a sense you would be right, for when you start looking, there is so much to see. But, as I would soon discover, the complexity and variation is pivotally useful when one square metre of land is different from the next. It becomes possible, by profiling the biological trace evidence, to identify the when and where of a crime, to pinpoint where somebody has been, when they were there, perhaps even – by the traces left on their clothes – what they were doing.

  And that was exactly how it was when, some weeks after the Chinese Triad case in Hertfordshire, I was in my laboratory when the telephone rang again, and that the same Glaswegian gruffness that now had a name – Bill Bryden – greeted me again. ‘Pat,’ he said, ‘if you haven’t had enough of us, something’s come up …’

  It is not always a murder. Murders make headlines but every day, somebody ruins someone else’s life somewhere by selfish or evil behaviour. And, on an overcast day in July that year, I found myself in a neat little square of shops, with flats above, in Welwyn Garden City, staring at the token municipal flower bed set into the paving stones. The roses planted as ground cover were pink and fragrant, but with dense, sharp thorns to keep off unwelcome residents. It struck me as being quite sweet and strange that young lime trees had been planted in the same plots as the roses. They make strange bedfellows. In nature, the chance of finding much lime pollen in the same sample as a lot of rose must be utterly remote. Generally, the pollen of the rose family is never abundant. It would be easy to conclude that this was an artificial habitat – a garden or park, although shopping centre would not be the first to come to mind.

  A girl claimed that a boy had threatened to kill her unless she agreed to have intercourse. They had been to a youth club together but, as in so many cases, his youthful testosterone surges had been uncontrollable. Most would be inclined to believe her as she was ravaged by deep scratches, and a large body-shaped impression had been made in the rose bed. No one in their right mind would lie in that bed of thorns willingly, but the young man steadfastly denied her claims, and I was asked to test his story.

  My ‘eureka’ moment with the hedgerow in the previous case might have opened my eyes to new avenues in palynology, but I had since returned to my laboratory and day-to-day work without any real sense of expectation. Academic work can be like that: a strange diversion, a weird digression, and then back to fieldwork, departmental seminars, the daily grind of counting pollen and spores that may have fallen into a pit or ditch in Roman times, or deciphering what the collection of pollen grains in a bronze vessel, dug out of a Fenland grave, might mean.

  Yet, in the weeks that followed, my mind wandered back to the murder. International gangs and money laundering, and a hapless attempt to hide a dead body: so far, so colourful – but the case into whose depths I was now staring was not nearly so absurd. This was just another of the ordinary evils people perpetrate against each other every day. I forced my thoughts back to this alleged rape and tried to imagine the scenario playing out in this little square of shops and flats – such an open and overlooked place. The boy and the girl had spent the evening together at a local youth club. After dark, walking home together, the couple had lingered here while their other companions departed, laughing, into the night. She said they had held hands and kissed. Perhaps it had gone further still. But when the boy pressured her for sex, she said no, and here their stories diverged.

  Two different versions of events: in one, the boy and the girl go their separate ways, each off to their own homes; in the other, the boy pushes the girl backwards, forces her down among those spiteful roses on the square, pulls off some of her clothes, and presses himself upon her.

  What was the truth?

  Rapes like this are extraordinarily difficult to prove. Where DNA evidence is not conclusive or does not appear to have been left at the scene, where witnesses cannot corroborate, or video footage does not allow, all the police have to go on are two stories, each battling with the other. Frightened or liar? Vindictive … or victim? Providing solid evidence for one or another can be almost impossible. And that was where I, on my second tentative ‘case’ for the police, was to step in.

  I had learned some (as far as I am concerned) dramatic facts in my first case: there is such specificity in an assemblage of pollen grains that one can envisage the place from which it was collected. Of course, this is something that I had been doing in archaeology for years, but I had never had any way of corroborating my ideas. Palynologists working on ancient materials can never really be sure that what they see in their mind’s eye is accurate. The past is past and gone. Now, I was excited to realise that I could check the validity of my interpretations – and I had discovered that the landscape can be recreated so exactly and, on such a small scale, that the potential it had for forensic investigation was vast. It was too exciting for words. In Hertfordshire, a group of organised criminals had been convicted by the pollen they had brought back on their feet to the car. Here, as I looked into the flower bed, my mission seemed clear. The boy admitted that he had been with the girl in the square, but denied that he had tried to rape her and declared that he had had no contact with any flower bed. Perhaps his shoes and clothes would tell another story.

  Both rose and lime rely on insects to carry out pollination and both plants produce relatively small amounts of pollen. This little fact was going to be significant in whatever I did. I knew that if rose pollen turned up on clothing, it was a good bet that the garment had touched a rose plant, or the soil immediately beneath it. If the plants had been widespread and wind-pollinated, it would mean that they shed their pollen further afield and it might have been spread across the square. This would have made it more difficult to declare, with any confidence, whether the boy had been in the flower bed itself, or just hanging out innocently nearby. Or would it? I needed analysis to find out.

  The hypothesis in cases like these might seem simple: if the pollen derived from the flower bed matched his clothes, in content and proportion, it would be likely that he had contacted the flower bed. But in reality, the challenge is much more nuanced, and getting a black-and-white answer would depend on the nature of the pollen itself.

  The morphology of rose pollen is so similar to its close relatives that, if any were about, it would have been difficult to separate it, with any confidence, from bramble, apple or hawthorn. Finds of it in ancient deposits are comparatively rare when compared to other plants so, if we found rose pollen here, and on the boy’s clothing, we might suppose that they could have come from the same place. Lime, too, is not as commonly found as that of, say, oak, hazel or pine. As far as I could see, there were no other lime trees anywhere in the vicinity of this part of the town so, if I found lime pollen on the boy’s clothing, there was a good chance that this was the place of contact. Because of the small amounts of pollen produced by the rose, and the fact that it is rarely found in any palynological profiles, allows us to consider it as being palynologically rare. The plant itself may be quite common but its pollen can rarely be found because it is collected and carried around by insects. Clover, with its heads of tiny flowers, falls into the same category. This is the way they have evolved, and forensic palynology can exploit this convenient characteristic.

  This was only my second case and I was on a steep learning curve. With the police, I made a grid on the flower bed and systematical
ly collected rose leaves and soil from each square. By doing this, I would be able to determine just how well each species was represented in the putative crime scene. Each sample was numbered, dated, timed, and placed in paper bags which were printed with police details on the outside. Detailed notes were made by the crime scene investigator while I drew a diagram of the flower bed and made my own notes about the sampling. I had been told that every little bit of scribbled paper must be kept if a case goes to trial, so I am always careful to save everything that might be relevant.

  There were no physical barriers, such as walls or other shrubs, so the process of sampling the square was straightforward – and, by the end of it, I had the necessary ‘comparator’ samples. These would enable me to test their similarity with that of the boy’s clothing. Invariably, a suspect will claim to have picked up pollen and spores from other places, the so-called ‘alibi’ sites. If this happens, it is essential to visit those places and collect ‘alibi’ samples for comparison with the crime scene samples, and from exhibits seized by the police. The only exhibits available to me were the suspect’s bomber jacket and his shoes. There was never any doubt about the identity of their owner; on this, at least, both boy and girl agreed. Getting the pollen out of the soil from the square was going to be relatively straightforward – I had done it time and again. In my archaeological work I had extracted good material for analysis from pottery and bronze artefacts. But I now had to think about doing the same from fresh leaves, a pair of shoes, and a bomber jacket, which was a mass of synthetic fabric and plastic. I would have to be inventive. I had certainly been used to that in both ecological and archaeological work.

  First of all, I had to envisage what went on during a rape. From what the girl had said, the boy had forced her down and lain on top of her. This meant that his elbows and the front of his jacket might be the best place to look for evidence. He would have knelt too, so his knees would have had direct contact with the leaves and soil. I surmised that the posture of the suspect during the putative act would have involved his knees, chest, elbows, and toes. His chest, elbows, and toes could be checked against his jacket and shoes, so there was a good chance that we would be able to accept or deny the suspect’s story.

  My logic was that if the defence claimed the pollen from the jacket had come from the air and by casual contact, the shoulders, back, and front, should yield very similar profiles. In other words, samples from the back of the jacket would provide good controls in testing the hypothesis that the observed profile from the front had been picked up from the flower bed. If the front resembled the flower bed and had minimal similarity to the back, this might be considered good evidence of contact. I tried not to predict the outcome; I just wanted to see the results. Back in my lab, making sure not to allow the various parts of the jacket to contact each other, I cut the sleeves away, and then the back. I was then left with two front pieces which I could combine into one sample.

  In those early days when I was taking tentative steps into the world of forensic detection, I knew very little about forensic protocols – those rules and regulations designed to make sure that no one had tampered with evidence, or that evidence was corrupted, or otherwise made unsafe during police handling. I had never even been in a forensic laboratory but, of course, I was well trained in laboratory procedure and, because of my background in microbiology, I certainly understood the basic principles of septic technique and prevention of contamination. It was just common sense to me, and I did not need any special tutoring in that.

  The brutal truth is that, even today, some police officers are woefully underprepared when it comes to handling some classes of evidence. They are taught how to take DNA samples and to prevent cross-contamination. They remember Locard’s idea – ’every contact leaves a trace’ – and know that contact between two pieces of evidence can render that evidence completely worthless in court. But, even now, after all these years of teaching them, they still cannot seem to get their heads around the constraints and requirements of environmental sampling.

  Many people have the wrong concept of forensic science, and the term is used in a very sloppy and inaccurate way. Perhaps you think ‘forensic’ simply means ‘carried out with great care’, but the true meaning of the word is actually much more specific. Court cases in Ancient Rome were held in the Forum, and the word forensic is derived from the Latin forensis, which means pertaining to the open court or public. So when we speak of ‘forensic’ what we actually mean is that any evidence produced will be pertinent to a court case. If a piece of work is not carried out with a view to it having some bearing on a court case, it is not forensic at all. And this is why such careful handling of the boy’s jacket was an absolute necessity. Whatever I discovered had to be uncorrupted and uncontaminated, and my training and experience in laboratory work over so many years meant that this concept was deeply ingrained. I use the same principles in my kitchen at home, and I am sure that no one would get food poisoning from my preparation of food.

  I did not need to evoke the ‘picture of place’ in this investigation. I already knew what the putative crime scene looked like. But visualising what had happened there in the square was critical to deciding how best to approach this, even though it did not need much imagination. I had already worked out which parts of the jacket and shoes needed to be processed and investigated. But, how was I going to get the palynomorphs out of the fabric of the jacket? I had never done this before. Years later, at a conference, commercial representatives were keen for delegates to examine their wares, and one being demonstrated was a microscope with a special attachment emerging like a long antenna that could be poked into restricted places. Its lens was powerful enough to see pollen grains directly without mounting them onto slides. I quickly went to the outside of the conference centre to get some pollen from the garden, and came back with some tulip anthers that were full and ripe. The representative dabbed some pollen onto a little piece of cloth and directed the antenna with its strong lens towards it. An audience had gathered to see what would happen and to everyone’s amazement, the pollen grains seemed to come alive. They wiggled and danced down into the weave of the fabric. I was astonished, but it made me realise why it was always so difficult to get palynological trace evidence from woven material. Mind you, this difficulty also means that pollen and spores provide excellent trace evidence because, unlike fibres and mineral particles, they become deeply embedded and are not easily lost. My subsequent work has shown that it can remain in all sorts of fabric for many years, and this is why palynology is such an excellent discipline in ‘cold case’ evaluations, where analysis may be needed long after a crime has been committed.

  Only after searching through the literature did I finally understand the reason for the pollen’s dancing behaviour. It is all down to electricity. Pollen is negatively charged and is, therefore, attracted to any positive charge. Bees are positively charged and (this is wonderful) they are attracted to flowers with the strongest negative charges. I had always assumed that the reason pollen stuck to bees was because of their hairiness and the stickiness of the pollen. Well, that may be part of the story, but there is little doubt that static electricity is also important in the transfer from flower to pollinator. The negatively-charged pollen jumps onto the positively charged bee through electrical attraction.

  Since those early encounters with the unknown, casework and experiments carried out by my M.Sc. students have shown me that many objects, fabrics, and substances will attract pollen strongly: human hair, fur, feathers, nylon and other synthetic fibres, wool, fleece (which is made from recycled plastic), plastic itself, and so on. Seemingly clean exhibits can have a heavy pollen load which, of course, is utterly invisible – but I am acutely aware of it, and nowadays I will never neglect any object in a criminal case. I once retrieved a few spores from a torch which had been used by a murderer while burying his victim. That torch yielded just a few pollen grains and spores but this was enough to tell us that he had laid it down a
t the edge of a fallow field – not much more, but that was enough for the clever investigator who eventually arrested him. Palynological intelligence can be powerful.

  All of that, though, was in the future. Right now, and without knowing any of this, I had to devise a way of getting evidence out of that jacket. I did not know where to start, but at least I was armed with a solid grounding in the types of things I was expecting to find. Pollen grains and plant spores are remarkably robust. They each have an outer wall made of a complex polymer called ‘sporopollenin’, and we are still not sure of its exact chemistry. As some palaeobotanists and geologists will attest, in the right conditions it can last for millions of years. A friend of mine, Professor Margaret Collinson, retrieved a whole bee out of Cretaceous deposits, and the pollen sacs on its legs, with all the pollen grains beautifully preserved, were clearly visible. The pollen was about 100 million years old but had been preserved in sediment that had consolidated to form rock. It is not only amber that can preserve insects.