The below mentioned article provides a study note on the forensic palynology.
Forensic palynology is the study of palynomorphs trapped in materials associated with criminal or civil investigations to solve criminal cases and resolve other legal problems. It also includes identifying and linking the suspect to the scene of the crime. According to Mildenhall, 1992 “The term Forensic palynology refers to the use of pollen and spore evidence in legal cases” — Bryant et al. (1998).
By extension the study of dinoflagellates, acritarchs and chitinozoans that are present in fresh water and marine environments are also included in forensic palynology. Most of these microorganisms are restricted to fossil deposits and sometimes provide legal information. Forensic palynologists seldom encounter these microorganisms.
Forensic investigators have lately employed the implication of pollen morphological characters in solving criminal cases. Most pollen grains are aperturate and each pollen grain and spore have definite shape, size, aperture and sporoderm stratification. The apertures have definite number, position and character (NPC). The exine often bears processes of various types, which form patterns and ornamentations.
With the aid of NPC, sporoderm stratification, size and shape it becomes possible to identify pollen. Identification includes family, genus and sometimes species or even smaller taxonomical units. Palynologists have sometimes called pollen and spore ‘the fingerprint’ of plants, as they are distinctive, easily recognizable and identifiable.
Most pollen grains fall on any exposed surface to the air. They may end up as components of soil and dust on objects. The types of pollen present at any one location, or on any object and their relative frequency will reveal the particular vegetation type of a site or a region. This is unique for a location, a larger geographical area or even a country.
In other words ‘pollen fingerprint’ of a region can be obtained from the pollen assemblage of that region. The pollen fingerprint is used as the control sample as it reflects the regional vegetation. It is this aspect that enables the forensic palynologists to compare pollen samples between a suspect, victim, object and localities. It also enables to prove and disprove a relationship between them.
The value of forensic palynology stands on the following attributes of pollen and spore. First, pollen and spores are produced in large numbers and so they are abundant in the atmosphere. Second, they are microscopic in size. They may be unknowingly taken away or left at a crime scene as evidence in large numbers.
They remain unnoticed, as they are microscopic. They cannot be removed from a crime scene. Third, sporopollenin is present on the walls of pollen where it forms species-specific-pattern. The pattern persists for thousands of years. Moreover due to the presence of sporopollenin pollen grains are very much resistant to damage and decay.
They get well preserved for many years in nature without specialized storage. The identifying characters like size, shape, aperture and sporoderm stratification remains unchanged after long periods of time and thus enables to identify a pollen grain. Fourth, pollen grains and spores can be identified to specific plant type, site, region or country.
To identify pollen and spores palynologists compare forensic pollen samples with references. The references may be in the form of slides, drawings and photographs published in literatures. Moreover a large number of Internet Websites provide images and description of pollen of regional vegetation.
A basic knowledge regarding the production and dispersal pattern of pollen of regional vegetation is extremely useful to the crime scene personnel. It enables the personnel to decide whether pollen analysis will be of any probative value at the crime scene in question.
If the pattern of pollen dispersal and pollen productivity of vegetation are known, then the expected pollen content of a forensic sample from that particular region can easily be predicted. If atypical species are present in the forensic sample, research is needed to find the reason behind the presence of atypical species.
Each plant has its own method of pollen dispersal. So the flowers may be hydrogamous, autogamous, cleistogamous, zoogamous and anemophilous. Accordingly the production of pollen per anther varies. Pollen, whose exine contains sporopollenin, are only preserved in long term sediments.
Pollen of hydrogamous plant lack sporopollenin and so rarely preserved. All the above criteria, i.e. methods of pollen dispersal, production of pollen per anther and presence or absence of sporopollenin are essential in determining the forensic potential of different plants. The forensic potential of plants with different methods of pollen dispersal is depicted in Table 5.2.
The ability of pollen to travel on air currents or to remain aloft is also extremely useful in forensic palynology. The ‘sinking rate’ or speed of a pollen grain determines it. The sinking speed is the rate of movement of a pollen grain while sinking to the ground and is usually measured as the distance travelled in unit time.
As for example, the sinking speed of Alnus, Betula pollen is about 2 cm per second. Several factors influence the sinking speed, e.g. the mass and size of pollen and their aerodynamic shapes, wind currents, humidity, obstacles in the movement and the height at which they are released from anther.
Researches reveal that 95% anemophilous pollen travel 25m to 100km and few may be carried thousands of kilometres. The small and light pollen move longer distances than the large and heavy pollen, because the fall or sinking speed of the former is much lower than the latter. So the potential distribution area of large and heavy pollen is small and restricted.
To explain the potential distribution area, Bryant et al (1998) cited the examples of Zea mays and Abies pollen. Pollen of the above plants are large and heavy. They fall to the ground or on any object fifteen times faster than the small and light pollen found in Alnus, Betula, Cannabis and Juniperus.
Studies show that the dispersion area covered by Zea and Abies pollen is smaller and more restricted than those of Alnus, Betula, Cannabis and juniperus pollen. The presence of large and heavy pollen like Zea and Abies in a forensic sample will indicate the small dispersion area.
This will enable to identify the source plant and accordingly the region. So, the forensic potential of anemophilous pollen may be poor or excellent and it depends on the association of plant types of that region from where the anemophilous pollen originated.
The value of pollen evidence in forensic investigation depends on careful collection, documentation and preservation for later forensic analysis of the collected sample (Fig. 5.4A). To obtain accurate results the forensic samples are collected and processed with great care. Forensic palynologists collect, store and analyze the samples with great precision.
Precautions are taken throughout all the steps to avoid contamination from atmosphere or other sources. The source material of forensic pollen may be almost anything that are exposed to or in contact with air. Even the packaged food and dry food like prunes, sultanas etc. contain pollen from where the food originated. The source material of forensic pollen is different for each case.
Lynne et al. (2005) published a detailed list of materials from where pollen in forensic cases were collected. Mention may be made of air filters, antique furniture, apricots, breads, Cannabis, carpet, car, clothes, colons, dirt and dust, dried fruits, fur, hair, honey, intestines, leaves, mud present on victim and suspect’s belongings, soil, wood, wool, weapons etc. Each item has an interesting case history and Lynne et al. (2005) illustrated many of them.
The collected pollen samples are stored in secure location to avoid any intentional switching or contamination. The result of forensic pollen analysis will guide the investigator to establish link between victim, suspect and crime scene using four-way linkage concept (Fig. 5.4B).
Crime scene documentation is necessary to establish the relationship of evidence to overall scene and other evidences. The documentations are usually in the form of photography, sketches, diagrams, general note taking and videotaping. Documentation is important for any type of evidence and it is meant to complement the other.
Forensic palynology has been utilized in many cases, e.g. assault, rape, forgery, drug dealing, armed robbery, fraud etc. In many cases mud, dust or dirt Collected from shoes, vehicles etc., for forensic evidence contain pollen from more than one locality. The pollen types of forensic samples are compared with the control samples of pollen assemblage from different region.
Thus it becomes possible to trace the region where the shoes or vehicles were present and to determine the travel history of the same items. Similarly pollen analysis from soil present on fingernail or clothing enables to reconstruct the recent movements of a person or animal. The travel history of a new car can be determined by pollen analysis.
Pollen, collected from a car radiator and their subsequent analysis, reveal the area and path the car traveled. The presence of similar type of pollen between the forensic samples collected from shoe prints and the shoes that made the prints indicate a match correlation. Pollen evidence is very much effective in crime scenes that are restricted to a few square metres, such as rape or burglary.
A comparison between forensic pollen samples collected from the entry point of burglary and suspect’s shoe could provide link in a case. In many cases pollen evidence prompted the suspect to confess to their crimes. In a crime scene it happens that the body was shifted to the present location from other locality where the crime occurred.
Forensic pollen analysis from victim’s clothing reveals the pollen assemblage from both the localities, i.e. the locality where the body was present and the locality of the crime. Analysis of pollen type in the stomach and intestine of a victim revealed what the victim ate in the last meal. Accordingly the time of death or location can also be determined.
Identification of pollen in stomach contents can be useful in verifying a person’s alibi. Pollen analysis of a honey sample has been used to authenticate it as labeled. Forensic palynology can also be used to prove or disprove alibis, narrow down a list of suspects, determine the travel history of items and drugs etc., determine the geographical source of drugs, fruits and various other things.
There are several actual court cases where pollen evidence became important clues that helped to obtain conviction. Erdtman (1969) describes an Austrian case where pollen evidence was the basis to discover the murdered victim’s body and convict the suspect. A man disappeared during a vacation at Danube, near Vienna.
During investigation the police suspected one with a motive for killing the missing person, who was the male colleague of the suspect. The suspect was detained while on a boat journey along the Danube River. But the police could not progress further without the missing person’s body or confession from the suspect.
Later search was made on suspect’s room and a pair of boots with mud attached to the soles was taken for forensic analysis. Geologist Wilhelm Klaus along with Austrian Geological Survey analyzed the mud sample attached to the boots. The sample revealed the presence of pollen both from a fossil and living plants. The living pollen grains were from pine and alder.
The only fossil pollen grain was from Miocene-age 20-million-year-old hickory plant. Fortunately one area was known where pine and alder pollen grew together on tertiary strata.
Klaus pinpointed a small area along Danube valley where such a unique assemblage of living and a fossil pollen grain occur in the mud. This is due to the fact that in that area an exposed tertiary stratum was present and that contributed the fossil pollen grain. Pollen from pine and alder mixed up with hickory pollen.
The suspect must have walked there and thus attached the mud on the boots. The identification of the area and the establishment of link between the mud from the area and from the boots of suspect on the basis of similar pollen composition prompted the suspect to confess to the crime.
In another case in Australia a man was physically assaulted near a river in southern Queensland. The victim and assailant rolled into the river. When questioned, assailant denied presence anywhere near the river. The forensic samples were collected from the river as control sample. An analysis of the control sample revealed the presence of algal cysts and other palynomorphs.
Forensic samples were also collected from the clothing of victim and suspect and the results of analysis of samples were compared with the control sample. All the samples, i.e. samples from river, victim and assailant had the same assemblage of algal cysts and other palynomorphs. This evidence prompted the assailant to confess to the crime.
Forensic palynology is also used to catch thieves. In New Zealand a rustler stole 300 sheep from a farm. Later a rancher who lived further north took 350 sheep to an auction for sale. The auctioneer knew the rancher. He became suspicious because the rancher’s farm was not large enough to accommodate 350 sheep.
The pasture can support about 200 sheep. The 350 sheep were impounded and the rancher was unable to show the bill of sale. He also failed to point the farm from where the sheep were bought. The rancher, who lost sheep, was asked to identify the impounded sheep. He inspected the sheep and believed they might be his sheep.
He did not brand the sheep by putting any identifying mark. So he could not prove his claim due to lack of any mark of identity. The rancher, who put the sheep up for sale, insisted that he had bought the sheep a week earlier though he could not produce any evidence of purchase. Police collected the forensic sample from the pastureland from where the sheep were stolen and from where the sheep were put to auction.
The pollen assemblage of these controls was analyzed. Forensic samples were also collected from the impounded sheep. Forensic palynologist sheared wool from small areas from the top of the backs and heads of impounded sheep and analyzed the pollen spectra of the wool.
The result revealed that the pollen assemblage matched the type of plants that are present in the region from where the sheep were stolen. The pollen evidence confirmed that the impounded sheep were not from the farm from where they were put to auction. Thus, the pollen evidence helped to support the claim of the rancher who lost sheep to the impounded sheep.
The following is a good example where pollen analysis has been used to establish the time of death. A mass grave containing 32 male skeletons were discovered from Magdeburg, Germany in the month of February of 1994. The identity of victims was not known. It was assumed that they died in a military interaction as all the skeletons were of males.
Two hypotheses were proposed: First, Gestapo at the end of World War II killed the victims in 1945 sometimes in the spring; second, the victims were Soviet soldiers. The Soviet secret police killed them in June of 1953 after the revolt of German Democratic Republic. It was very critical to determine whether the soldiers were killed in spring or in summer.
The skeletons were dug out of earth. Forensic control samples were collected and analyzed from the soil from where the skeletons were recovered. Forensic pollen samples were also collected from nasal cavities of exhumed remains to determine pollen that were inhaled before death. The nasal cavities were ringed with saline solution and thus pollen were collected.
The forensic sample collected from the nasal cavity contained high amounts of pollen from plantain, rye and lime tree. All these plants flower in summer. Pollen analysis supports the second hypothesis. The skeletons were of Soviet soldiers. The Soviet secret police killed them after June 1953 revolt.
The following is the case example where pollen evidence narrowed the search list. A European company exported some machineries by sea to a location in Asia. The machinery was packed in wooden crates. On the way the ship stopped at a number of ports. At each port various cargo was loaded and unloaded. On reaching the destination it was found that the wooden crates contained soil bags only.
Pollen types present on the soil were analyzed. Pollen analysis revealed the plants that are present in South Africa. The results of pollen analysis narrowed the search to Cape Town, the only port in South Africa where the ship stopped. Though the ship stopped at many other ports but they were away from South Africa. After several months the machineries were recovered from a warehouse in South Africa.
The above are a few illustrations where pollen evidence is used to solve crimes and resolve other legal problems. The forensic applications of palynology are almost limitless. Literatures and a large number of Internet Websites provide many case histories throughout the world. Pollen evidence is now accepted in courts of law.
Pollen evidence has helped in solving several cases of murder, rape etc. in Sweden, New Zealand and many other countries. New Zealand leads the world so far as the forensic application of palynology is concerned. In India forensic palynology has not received much attention. If due attention is given many cases of rape, murder, kidnapping, adulteration of food and other eatables such as honey, milk etc., can be solved easily.