Traces

by Patricia Wiltshire

  Eventually, the crime scene was found, and the grass identified from its leaves. After testing the various grasses at the site, my fellow palynologist on the other side of the world found at least two plants where all the pollen had two pores. None of us had ever come across this phenomenon before and, with so many palynologists in the world, something like this would have certainly been reported in the literature by now. These grasses with the two-pored pollen had undergone some kind of mutation to produce such abnormal grains, and it is possible that they had, at some time, been treated with some mutagenic chemical, possibly a weed killer. I find that really frightening. I wonder if such a substance could cause mutagenesis in the sex cells of other plants and animals – even human sperm? After all, as bizarre as it seems, we are related to grasses (though distantly) and some of the processes in pollen formation also occur in sperm production. In any event, these mutant grass grains were marvellous identifiers of a place. And, if two-pored grass pollen was found on a suspect, he would have a lot of explaining to do to convince the police that he had not contacted the crime scene. Like many other cases, however, a suspect was never apprehended.

  Crime scenes change over time. In one dramatic case, a senior investigating officer in the north of England desperately wanted me to evaluate a crime scene in the brutal murder of a prostitute. It was the weekend, there were no flights, and it would take too long for me to drive all that way north, as this was an urgent case. Thinking out of the box, the senior police officer got in touch with Surrey Police and asked them to bring me in their helicopter. The journey was very quick, but also vastly more interesting, and certainly more fun, than travelling by road, except for having to wear huge safety flying helmets. When we arrived at our destination, my picture was taken as I stepped out of the helicopter. I would have loved to look like a glamorous aviator instead of the bulbous-headed midget that stepped out on that windy tarmac.

  A waiting car whisked us to the deposition site where groups of officers were huddled around, kicking the ground and probably dying to have a ‘fag’. A smiling CSI greeted me.

  ‘I’ve cut all the grass and bushes down for you, Pat!’ he declared. I laughed as I struggled into my Tyvek suit.

  ‘That’s a funny one.’ But, he was not joking. The smile just faded from his face and he stared at me blankly. He had cut back the whole crime scene, contaminating everything, and lost all the evidence I might have found where the body had lain. Not only had the vegetation been cut right back, but it had been dumped, in a complete mishmash, on the only path that might have been taken by the offender. The senior officer came over and was tight-lipped with exasperation. He was as incredulous as I was.

  Conversely, here in North Wessex, almost a month had passed since the alleged incident had occurred, and this, in itself, could have posed a conundrum. Nature, after all, is constantly striving: plants continue growing and spreading, changing the look of places beyond all recognition; earthworms keep depositing soil on the surface; plants may die and even disappear.

  Thankfully it was high summer and, because I was called fairly soon in this case, the alleged crime scene in the strip of woodland had had little time to change significantly. Unfortunately, this was not the case in the park, just about 200m away where the boy claimed the girl had been so willing. The Council had mown the turf but the ground was still strewn with grass clippings, with fairly large amounts of clover and hop trefoil, a little yellow-flowered plant related to the clover. The surface of the site which formed the boy’s alibi was only represented by the grass cuttings. Although mown, they represented the surface that would have been lain on by the couple. The suspect was very specific in identifying the spot where he claimed they had enjoyed themselves. This meant that I could take my comparator samples from exactly where their bodies would have contacted the ground.

  Comparing the two sites with profiles built up from the clothing of the accused man and his accuser would, in principle, allow me to answer the critical questions: was the man telling the truth when he said they had lain down together in the park, or should the woman’s story – that they had been together in the wooded area between the houses – be believed? But in life, things are rarely ‘either/or’ scenarios, and so it was here. The question was complicated by the fact that the ‘Snoopy’ pyjamas the man had been wearing over his jeans (we never found out why) had been discarded, later to be found hanging over the branches of a Cotoneaster shrub at the edge of a nearby garden – perhaps corrupting whatever trace evidence we might derive from them. The situation was complicated even further by the fact that, after the incident, both victim and alleged attacker agreed that they had sat together on the verge outside her home, potentially collecting more contaminating trace evidence there. All of these places would have to be sampled in the hope that we could eliminate them from our investigation. At the two ‘crime scenes’, and all the other places the girl and boy were said to have visited, or contacted, I made species lists of all the plants that I thought could possibly have contributed to the forensic trace evidence.

  Here we had two sites, one represented by grass cuttings and the other of soil mixed with woodchips. To get as close to the true ‘picture of place’ as possible, it is essential to take multiple samples because from experience I know that, in terms of biological content, the surface of the ground, and the soil itself, is extremely patchy over very short distances; one sample would yield only a fragment of the available information. I was very lucky that here the two most important sites were small and well-defined, and I could indulge in taking a good complement of surface samples, each one being carefully recorded, with everything photographed as we progressed. The greater the area analysed, the closer one comes to the truth.

  It was very hot, I was sweaty, and the work was incredibly tedious, but that is exactly what forensic science is like most of the time. One also has to keep focused, making sure that nothing has been forgotten. In court, anything overlooked or disregarded could be highlighted, picked on, dissected, and thrown down disdainfully as a challenge.

  All the case samples were duly delivered to the laboratory, and the task of getting the pollen grains from the clothing, and out of the comparator samples, began. Such retrieval is a dangerous business as it involves treating the sample with very strong alkalis and acids, including, among others, caustic soda, acetic anhydride, glacial acetic, hydrochloric, sulphuric, and hydrofluoric acids. The latter is horrendously dangerous as the vapour can dissolve your lungs, and the liquid can go right through skin and dissolve bone. It is used in glass etching and, in our work, it is needed to dissolve the quartz out of the soils. Hydrofluoric acid can work its way through glass and metal – it reminds me of the corrosive slime that dripped from the monster which burst out of John Hurt’s chest in the film Alien, when it went right through the hull of the spaceship.

  In hydrofluoric acid, we have the potential for a real-life horror story. Using it requires a high level of protective clothing and a mask, and everything must be done in a fume cupboard. There is a shower nearby, special ointment, and a hotline to the local A&E department of the hospital. You have to be quite robust to do this kind of work and what amuses me is the traditional stereotype of a botanist – tweed skirt, hand lens, stout shoes, and a mild, gentle disposition. In Jurassic Park, the ‘love interest’ was an archaeobotanist, and little E.T. was a botanist from outer space, both resourceful and portrayed as mild. I would love to be thought of as being sweet, mild, unchallenging, and gentle. I think I am gentle, but nothing else fits. People with those characteristics make lots of friends but do not do well in court, where the opposition invariably seem like brutal bastards.

  The chemical processing did not present any problems and, eventually, long rows of microscope slides were lined up along the workbench. Now, the long, gruelling counting with the microscope could begin. In every field of view, everything is identified and counted. Sometimes, a palynomorph will elude identification, in which case it is logged as ‘unknown
’ and is revisited after counting is complete. If deemed important, long hours can be spent in trying to track it down. Sometimes, I exchange pictures of an unknown with other palynologists in case they know its identity, particularly to colleagues Vaughn Bryant in Texas, and Dallas Mildenhall in New Zealand, and they reciprocate when they get stuck too. Sometimes, the palynomorph may elude identification by any of us, in which case it is tallied as an unknown. That is the only way to provide credible data. One cannot afford just to make guesses; the outcome might affect someone’s life drastically. If the clothing and footwear profiles from each party resembled the park more than the woodland, then it was reasonable to suppose the boy was telling the truth. On the other hand, if they resembled the woodland profile more, then the evidence would support the girl’s testimony.

  I started on the comparator samples just to get an idea of the range of taxa I could expect, and to see if they married up with the species lists I had made in the field. That is always of critical interest because it enhances interpretation. The big surprise was that the very open park site, which had a margin of mature trees and few barriers to pollen dispersal, had very little tree pollen in the profile; grasses, nettle, ribwort plantain, other herbs, ferns, and mosses dominated the results. The surprisingly large pollen grains of clover were much in evidence, but I knew that this plant had been growing abundantly in the turf. I had not even noticed the other herbs, so their pollen must have been finding its way into the middle of the park from the edges; the only plants growing in the immediate site were grasses, hop trefoil, plantain, and the clover.

  When it came to the enclosed, wooded site, the putative crime scene, it was enclosed in trees and shrubbery. Such vegetation nearly always proves to be a barrier to free pollen flow from outside, but I found 28 different woody plants in the surface soil and litter samples. Pollen from the gardens running down one side of the road had found its way into the site and it was interesting to see how far Ceanothus pollen had travelled, and how much cypress pollen had blown onto the surface soil and litter. The only herbaceous plants of note were cow parsley and buttercup, and they were certainly on my list.

  It was useful that the pollen profiles from both sites were so different but, although the pollen results were startlingly good, the stark and amazing differences demonstrated by the fungal spore assemblages were even more dramatic. The alleged crime scene revealed a vast range of fungal spores, most of them associated with woodland floors, where dead twigs, branches, rotting leaves, and other debris provide perfect conditions for fungi. Among the 21 separate species of fungus identified were the cylindrical, pale brown spores of Camposporium cambrense, a common fungus on rotten deciduous tree debris, like birch, holly, and oak; Brachysporium britannicum, a common smooth-walled species known from the bark of ash, beech, birch, chestnut, and oak; and, most intriguingly of all, Clasterosporium flexum, a fungus whose spores have only been reported six times in Britain, and is found on the decaying leaves of the alien cypress.

  Finding such a rarely-encountered fungus here might not have been a surprise – there was, after all, a cypress tree growing in a garden immediately alongside the alleged crime scene – but rare palynomorphs provide extraordinarily powerful trace evidence in the world of forensic detection, helping us to make precise correlations more effectively. And nor was this the only rare spore identified here: Pestalotiopsis funerea, a parasite of the cypress tree, was there in the assemblage; and so was Glomus fasciculatum, a fungus found exclusively in soils and, although extensively found in European woodlands, there have only been four records of this particular species of Glomus in Britain. Its rare status was a vital signifier to us. If these spores, which were virtually all characteristic of woody detritus and woodlands, were in the samples from the clothing belonging to either party, we could more confidently place them where the girl said she had been raped.

  Crucially, the samples from the park yielded few of these particular fungal spores and, in fact, the ones that dominated our comparator samples from there were much more common: Epicoccum nigrum, growing prolifically on the grass cuttings left in the turf, Cymadothea trifolii, a fungus specific to clover; and Melanospora, a fungus that ordinarily parasitises other fungi growing on herbaceous plants. The two sites might have had some overlap in terms of their pollen profiles, but their fungi seemed discrete and different.

  With rich profiles for our comparator samples established, we could move to the next phase of the investigation: determining which palynomorphs were on the clothing that might persuasively place them in one or the other location. I decided it was necessary to analyse as much of the clothing from both the girl and the boy as possible. I had their footwear, jeans, tops, fleecy jacket, and the bizarre pair of pyjama bottoms. If the clothing and footwear profiles from each party resembled the park more than the woodland, then it was reasonable to suppose the man was telling the truth. On the other hand, if they resembled the woodland profile more, then the evidence would support the alleged victim’s testimony.

  Both sets of clothes had picked up an immense amount of palyniferous material. As the count began, a distinct image formed: the man’s jeans, pyjama bottoms, and trainers revealed an abundance of taxa we had already identified from the alleged crime scene. And soon, I began to see the same assemblage from the woman’s clothing.

  The pollen profiles were excitingly comparable. There will never, ever, be an exact match between the samples, but the strength of palynology as a forensic technique is that there are very many markers to take into consideration for interpretation. We are not just looking at one item of trace evidence, as is often the case with fibre trace evidence, or a single gunshot particle which was so pivotal in the Barry George/Jill Dando case. Each palynological profile might contain as many as 200–300 or more separate units of evidence. Collating and calculating the results from the count data is the most exciting and interesting part of the whole investigation for me.

  It is the final picture that makes everything worthwhile and, in this particular case, the results were quite spectacular. The ‘Snoopy’ pyjamas yielded a huge amount of pollen from the rose family and this could be explained by them having been flung over the Cotoneaster bush which was in full flower at the time. All the trees and shrubs found in the wooded area were also extracted from clothing of both the girl and the boy, especially oak, birch, pine, and elder bush, the four dominant pollen types on the woodland floor.

  I was also taken aback at the evidence of contact with the wooded site provided by the fungal spores. Having fungal spores as well as pollen results from each sample meant that we had two distinct classes of forensic evidence, and this made it an exceedingly powerful data set; and the fungal spore results were as spectacular as those of the pollen and plant spores. The botanical and fungal evidence supported each other.

  It was intriguing that the absence of certain taxa was as important as the presence. Spores of the fungus Epicoccum were overwhelmingly abundant in the grass cuttings, but only one spore was present in the samples from the wooded area. Its virtual absence in the woodland, and very poor representation on the clothing, was significant. With such huge amounts of Epicoccum spores in the grass cuttings, neither the girl nor the boy could have failed to pick up large numbers if they had, in truth, lain on the grass. It was the same with the clover pollen. There was a large abundance in the grass cuttings yet, again, the clothing and footwear of both parties yielded only a single grain. This massive difference for clover was as important as the Epicoccum spores.

  Compared to the park, there was a huge amount of dead, twiggy litter under the trees in the wooded area, and the testament to this habitat was the large number of different fungi which grow on dead wood of various kinds. Further, although microscopic themselves, most of these fungi produce large spores which are not dispersed freely into the air and, if they are picked up, they represent excellent local indicators. The belongings of both the girl and the boy yielded a very wide range of fungal spores that were just
not found in the turf of the park and, in particular, the two decidedly rarely found fungi, Clasterosporium flexum and Bacterodesmium betulicola, so characteristic of dead wood, were important finds. There was more on the girl than the boy, presumably because her body had had greater contact with the ground than his. For these fungal spores to be transferred, there must have been direct contact with the ground in the putative crime scene.

  Although there were some traces from other places, and some in common with both sites, there were 115 individual palynomorph taxa to substantiate the girl’s story. In the knowledge that, in my 25 years as a forensic palynologist, I have never had two locations yield the same palynological profile, one must ask what is the likelihood of two people achieving these profiles by chance from randomly chosen sites? The pollen and fungal spore profile obtained from the girl’s clothing closely resembled that from all the boy’s clothing and footwear. Then, both sets of clothing were much more like the woodland profile than that of the park. This merely confirmed the story that they had both lain together in the wooded strip of land, and the putative crime scene then became a real one.

  We do not need perfection to have the confidence in our findings. Nature has given us a messy, imperfect world and rarely, if ever, do things match exactly. Yet there was no denying the strength of the correlation we had uncovered here. The assemblage on the suspect’s and alleged victim’s clothing closely resembled each other and, taken together, they closely resembled the samples we had taken from the woodland – the place where the girl had claimed rape.

  I cast myself back to that space between the trees, overlooked by the manicured middle-class gardens where alien species of tree and shrub were in full flower. Of the two places, this, I was sure, was where the two had wrestled on the ground together; it was here, in the shadow of these trees, picking up the pollen and spores from the debris littered on the ground, that they had struggled. We might not have had witnesses. We might not have had testimony we could rely on. In another era, this might have been a cut-and-dried ‘him versus her’ case, the kind that will almost always fail the ‘burden of proof’ test that is so critical to our courts. But what we did have was a picture, built up from pollen and spores, of where these two young people had been, of the unseen nuances of their surroundings that their clothes and bodies had rubbed up against. Nature had left its imprint on them and that was enough, in the eyes of the law, to corroborate one story beyond reasonable doubt, to vindicate a victim and expose an accused man as the rapist he was.