It was late and dark and she was sure she was being followed but as she rounded the corner and went down the side street the footsteps did not appear to follow. What she did not know was that there was a short cut from the main road to a spot further down the side street and that was where he was waiting. As she passed the alleyway he pounced, grabbed her and dragged her into the dark alleyway. She screamed. He threatened to kill her if she screamed again. They struggled. She was raped and violated several times and left injured, dazed and scared to move, her clothes ripped off and scattered around her. By the time she composed herself and sought assistance the assailant was well gone.

She was able to give the police a good description of the assailant and an arrest was soon made. The suspect admitted that he had been in the area and that he had seen the girl. She had appeared a little distressed and he had asked her if there was anything wrong and could he assist. She told him that she had just had a fright and was okay now. He must have been the first person she saw and she must have put my face onto the face of the assailant, he said to the Police.

This incident is based on an event that happened in one of New Zealand's largest cities. It is typical of such attacks that happen, unfortunately, more often than we would like in all countries. In more cases than we would like to admit it is difficult to prove that the suspect was ever at the scene of the crime, particularly when no bodily fluids are left at the scene. Invariably in such cases the suspect's clothing can pick up microscopic remains from the scene. These remains can occasionally be either unique or highly unusual and "fingerprint" the suspect to the scene.

In this case the Police had little to go on. The suspect denied having entered the alleyway - there was no reason why he should be there, he was just a passer-by in the wrong place at the wrong time. There was no DNA evidence and since he had admitted to seeing and helping her any hairs from body or clothing that may have been exchanged was of little use. There was the evidence of one pubic hair on the victim matching the prime suspect. What else could the Police use?

The area where the rape took place was an asphalted alleyway, leading to several properties, lined on one side by a garden of exotic horticultural shrubs. Parts of the plants had broken and were spread over the asphalt. During the struggle the pair had rolled into the garden. Some of the plants were in flower.

The Police had as a matter of course taken all the suspect's clothing. His jeans and T-shirt had dirt stains and the Police thought that these may have come from the scene. They cut out the dirty patches and sent them to forensic scientists, along with a control sample of dirt from the crime scene, to see if any match could be obtained, but mineral and clay analyses of the soil could not pinpoint an area as specific as the Police needed.

Next, the samples were sent to the forensic palynologist, a scientist who studies the legal aspects of spores and pollen, to see if the scene had a signature or fingerprint that could be picked up on the suspect's clothing. The control sample and pieces of cloth cut from the jeans and T-shirt were subjected to chemical treatment and centrifuging, concentrating the spores, pollen and other organic material. This material was mounted in a preserving medium under cover slips on glass slides and examined under a high powered light microscope. The different spores and pollen were identified and their percentages calculated. The control sample from the scene indeed proved to have a signature that if found on the clothing of the assailant would be difficult to explain unless he had been there.

The control sample contained a large number of fungal hyphae, fruiting bodies and spores, including a large, three-pored, thick-walled spore. The pollen was dominated by the Northern Hemisphere species Artemisia arborescens (77%), a plant that was subsequently identified by the palynologist from police photographs taken of the scene and from pollen samples taken from the vegetation growing there. A. arborescens in New Zealand can grow to almost 2 m in height and has distinctive deeply incised, narrow, whitish leaves and stems covered in dense hairs. The natural distribution of Artemisia is in arid areas of the United States and South America and on the steppes of Europe. A lot of the Artemisia pollen was still in clumps indicting that the source of the pollen was at that scene. No other individual fern spore or pollen type formed more that a few percent. The identified spores and pollen were light-coloured and contained cell contents. Mixed with these were very poorly preserved darker etched grains that were a year or more old and lacked cell contents.

Then the jeans were sampled and compared with the control sample. Material from both samples had the same range of preservational characteristics. The spores, pollen and other organic material were a mixture of dark, poorly preserved and light coloured, well preserved spores and pollen dominated by pollen of Artemisia arborescens (53%), many with cell contents still intact. Again the Artemisia pollen grains were in clumps. It is unusual to get 50% Artemisia pollen on the ground, unless samples are taken from directly under a flowering plant, let alone on clothing. The same three-pored, thick-walled fungal spore was also abundant. There were other pollen grains found on the jeans, primarily pollen from various daisies and the myrtle family, that were not found at the scene. Other grains were expected as the small 35 x 40 mm piece of jeans material was processed intact to obtain the pollen, and the cloth would hold pollen collected since its last wash and possibly before.

Because the jeans contained such a large amount of Artemisia pollen, it was decided to process the piece of cloth cut from the T-shirt. This measured 200 x 110 mm. Preservation of the organic material was the same as the organic material from the jeans with many of the pollen grains retaining their cell contents. Thirty-one percent of the pollen sample consisted of Artemisia pollen and there were a few grains of the three-pored, thick-walled fungal spore. Again, so much Artemisia pollen was present that the clothing had to have been in contact with the parent plant. A lot of different pollen types, including daisies, grasses and myrtles, were also located. Since this piece of cloth was so much larger than the jeans material many more pollen and spores grains were collected, diluting the percentage of Artemisia pollen from the crime scene. What were the chances of the suspect having such a large percentage of Artemisia pollen on his clothes without ever having visited the scene? We can approach this question in several ways.

First, Artemisia arborescens is not a common plant. It is grown in New Zealand as a decorative shrub so it can be found occasionally in private and public gardens. Investigations showed that this plant did not occur anywhere near the usual haunts of the suspect. His explanation for the mud and pollen on his clothes was that he wore them while servicing his car in the backyard of his flat. This backyard consisted of a lawn surrounded by a fence on which ivy grew and along which a few native plants occurred. No Artemisia shrubs were located in the area.

Second, the chances of someone picked off the street at random having such a large percentage of Artemisia pollen on them was considered. In our laboratory we have processed over 1000 recent samples from many sources around New Zealand and Artemisia has never been found in more than trace amounts, and only then in less than 10 samples. No modern samples from the northern hemisphere, examined by us in New Zealand, contain Artemisia pollen in the numbers obtained in this case. So we can say that at the least it would be one chance in a thousand and certainly the chances would be immensely higher than this.

Third, what are the chances of pollen randomly attaching themselves to the clothes? Artemisia pollen is wind-dispersed but most of the pollen falls within a few hundred metres of the parent plant and gets diluted very quickly by all the other air-borne pollen types in the area. Not all pollen from an individual plant is dispersed at the same time so vast quantities are never carried in the air at any one time, unless a large percentage of the area is cover by many Artemisia plants. In New Zealand this is never the case. Also, since the clothing of the suspect had clumps of Artemisia pollen this indicated direct contact with the plant as the pollen would only be blown around as individual grains. Given the percentages on the clothing, it would be extremely unlikely that any clothes would have such a huge percentage from random gathering of pollen. The fact that many of the pollen grains still had intact cell contents indicated that the grains had arrived on the clothing within the last few months at the most.

Fourth, would it be possible for the suspect to have obtained this large percentage of Artemisia pollen on his clothing through random contact with a plant that we knew nothing about? It is highly likely that a chance brushing against an Artemisia shrub would result in the pollen attaching itself to the clothing. The suspect would have to be wearing the same jeans and T-shirt and the pollen would have to attach themselves to the same spot of dirt on both items of clothing. No Artemisia pollen was found on a control sample of cloth from another position on the jeans. For the pollen to still be in clumps, not subsequently brushed off, associated with spots of dirt, and in such high percentages the contact would have had to be prolonged and with a degree of force to ingrain the dirt plus pollen into the clothing.

Finally, there were all the large, three-pored, thick-walled fungal spores. These too were on both the jeans and T-shirt. These types of spore are not commonly found on clothing, and never in the percentages seen here.

Taking the physical evidence of a broken bush of Artemisia aborescens at the crime scene, the chances are astronomically small of picking a person at random with: a. 31%-53% Artemisia pollen occurring on their clothing; b. that pollen being in clumps indicating intimate contact with the source plant; c. that pollen containing a large percentage of specimens with intact cell contents indicating recent contact with the parent plant, and; d. the pollen being associated with an unusually large percentage of one type of fungal spore.

Therefore the evidence strongly supported the idea that the soil on the jeans and T-shirt came from the crime scene represented by the control sample.

Also at the scene were flowering pelagoniums. Pelagonium pollen were found on the jeans and T-shirt but oddly enough did not occur in the control sample. The pelagoniums were growing immediately underneath the Artemisia. The flowers had not released their pollen but were crushed during the struggle and pollen released onto the clothing of the suspect.

These conclusions were presented in court and were accepted as being undisputable evidence indicating that the suspect had to have been at the scene, and was therefore the assailant. He was to be sentenced to eight years' imprisonment.

Palynological evidence may not be able to prove that a crime has been committed but it can provide valuable evidence that can help the Police come to an understanding of what has happened at a criminal scene. Not all palynological evidence will be useful in a court of law, but it can still provide or change the directions Police enquiries may be running. There are only a small number of experts in the field of forensic palynology but they could be used more frequently. Scene-of-crime police and forensic scientists could be more aware of the potential for forensic palynology and routinely consider its use. The more quickly control and evidential samples can be collected the better, and there is a strong case for the automatic collection of control samples at crime scenes in case forensic palynology is subsequently needed to help identify, link, and place suspects at a crime location.

There are many ways in which palynological evidence can be acquired and the events described above are but one possible scenario. A portfolio of cases has now been documented and these are available on request. For another application of forensic palynology, take a look at http://www.gns.cri.nz/news/release/forensic.html.

For further information contact:

Dr Dallas Mildenhall
Institute of Geological and Nuclear Sciences
P O Box 30 368, Lower Hutt, New Zealand
E-mail: mildenhalld@wpo.gns.cri.nz
 

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  This article first appeared in CAP Newsletter 21(2):18-21, 1998.