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Comparisons of inks and paper: Inks can be analysed for the pigments they contain, but more usually for the age of the ink. Paper has been traditionally examined with the microscope, but a revolutionary new technique, called the Video Spectral Comparator 2000 is capable of detailed analyses of both papers and inks.
EXPLOSIVES:
If a sample of powder is found, it is collected as if it is a drug. Samples of powder are collected in plastic bags or vials; liquids in vials. Plant material is submitted in paper bags, as enclosure in plastic bags will lead to decay.
Chemical tests are available to identify drugs such as amphetamines, barbiturates, cocaine, LSD, marijuana and opium derivatives. Microcrystaline testing: The substance to be tested is mixed with a drop of a chemical reagent on a microscope slide and left until the chemical reaction that occurs produces crystals. The crystalline structure is viewed with a microscope and is highly specific for a wide range of drugs. This type of testing is more specific than colour testing – several hundred tests are available. Chromatographic analysis: Drugs are often mixed with other chemicals, called diluents, frequently sugars or starches. Simple solvent extraction and thin-layer chromatographic techniques can be used to separate drugs and diluents.
An explosive is a substance that through chemical reaction liberates much energy. Explosives may be divided into two types:
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Low-order explosives. With this type of explosive, the rate of energy change is relatively slow and the substance must be in a compressed or enclosed state to explode. Low-order explosives produce large chunks of debris and include gunpowder, smokeless powders, volatile flammable liquids, and flammable gases. A dust or grain explosion is also considered to be a low-order explosion.
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High-order explosives. With this type of explosive, the rate of energy change is very rapid, and everything nearby is pulverised. High-order explosives include dynamite, military explosives, TNT, PETN, Composition C, and mixtures of ammonium nitrate and fuel oil.
The forensic scientist will be looking for residue from the explosive in debris and soil close to the point of detonation. Any unusual odors are noted. An examination of accessories such as blasting caps, wires, batteries, fuses, containers and boxes, etc. sometimes makes it possible to identify the manufacturer.
The effects of the two types of explosives are quite different - low-order explosions tend to eject material rather than shatter, resulting in large chunks of debris. The twisting and tearing of objects tends to result from the explosion. High-order explosives shatter and fragment material, and there is much evidence of impact by fragments from shattered objects effectively converted into small, high-velocity missiles.
Determination of the type of explosion can often be done on site. Debris taken away from the scene is examined to find traces of the explosive. Debris is cleaned with acetone (propanone) which will dissolve most explosives. The most common technique used for analysis is chromatography. Gas chromatography involves converting the chemicals to gases at the operating temperature of the instrument. If the suspected compounds would break down at these operating temperatures, high performance liquid chromatography (HPLC) or infrared spectroscopy is used instead. Thin-layer chromatography is also used in some instances.
FIBRES:
If a body tissue sample (or anything of that sort) is found:
Sometimes, for instance in cases of sudden deaths and suspected poisonings, it is necessary to analyse organs, tissues and/or body fluids. At post mortem, the pathologist removes, and sends specimens of various body tissues and fluids to the forensic toxicologist for examination.
The many techniques available for this area of work include gas and high performance liquid chromatography, scanning electron microscopy, emission spectroscopy and atomic absorption spectrophotometry for the detection of heavy metals such as mercury and lead common in poisoning cases. One of the most important and accurate devices used in this area is the mass spectrometer.
Fibres can be natural and obtained from plants, e.g. cotton, linen, or animals, e.g. wool, silk, or man-made, e.g. nylon, polyester, etc.. As a general guide, natural fibres tend to have a rough and irregular appearance, while man-made fibres are longer and smoother.
It is standard practice to take samples of fibres from the scene of crime, as these identical fibres may later turn up on a suspect’s possessions. These fibres may be from a carpet or have been woven or knitted into a fabric used in clothing.
Since fibre evidence is generally small in nature, care should be taken to prevent loss or contamination. Several methods are used in the collecting of fibre evidence - visual searches, searches using alternative light sources and searches with additional magnification. Recovery of evidence should use the least intrusive technique practicable. This could include picking, taping, scraping, or vacuuming. Clothing or other items having adhering fibres should be wrapped carefully if being sent to the laboratory.
When examining fibres, the forensic scientist may use a special microscope called a comparison microscope – two microscopes linked by an optical bridge - so that a direct comparison may be simple. For man-made fibres, analytical chemistry techniques may be used. For colourless fibres of polyester, for instance, melting-point and refractive index determinations may be used. The material is scanned with up to ten different wavelengths of light and recordings are taken of the position of fibres that match the absorption characteristics of a number of known fibres. If a larger sample of clothing has been left behind, then the weave of material may also provide useful evidence.
If the samples from crime and suspect match, the probability of the suspect’s guilt then has to assessed – if the fibres came from a garment from a chain store, this evidence may have to be taken in conjunction with other types.
FINGERPRINTS:
The discovery that no two people – not even identical twins – have the same fingerprints was one of the most important discoveries in the history of forensic science. This has been known in ancient China and Babylon, but it was not until a scientific paper by Scottish physician Dr Henry Faulds that modern fingerprint analysis began. The first serious study of fingerprints was by English scientist Sir Francis Galton (see also Unit 6), who laid the foundation of a classification of fingerprints. He identified 3 basic patterns – arches, loops and whorls, and a police officer in India, Sir Edward Henry, added two more classes. With this new system in operation by 1896, crime detection in India soared.
Print evidence is fragile - a touch would destroy one. Items found in water, snow, or mud may also yield prints, but before you any attempt to process it or pack it for shipment to the crime lab, it must be allowed to air dry. For latent prints, the biggest problem is to make them visible. However, if left untouched, they are virtually permanent – latent prints have been found in ancient Egyptian tombs!
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Dusting. Dusting is ideal on non-porous surfaces. Powder is dusted lightly over the surface on which a print has been left, and sticks to the oil and sweat and so brings out the pattern. Once you locate a print, the powder is very gently brushed off. The powdered print can then be photographed or lifted - adhesive material, such as Sellotape, is applied to remove the powdered print from the surface.
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Iodine fuming. This works well on porous surfaces such as paper. The material is exposed to iodine vapour, which reacts with the sebum to produce yellow-brown prints. The prints are non-permanent, so must be photographed.
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The ninhydrin spray. This is a particularly useful method for all kinds of surfaces, including books and wallpaper, and is designed to develop prints that may be very old (30 years plus). Ninhydrin reacts with amino acids from sweat and produces various shades of blue-purple when developed.
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Silver nitrate. This picks up salt in sweat. This can be sprayed onto a surface, such as wood or cardboard, or it can be applied with a brush or swab. It is allowed to dry for about five or ten minutes, then exposed to ultraviolet light (or sunlight). Prints developed this way also disappear after a short time, so have your camera ready.
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Superglue fuming. Superglue vapour reacts with water in the print. A few drops of superglue are placed on a hotplate in a glass tank. The object is then placed in to the tank, and in about fifteen or twenty minutes, any prints that were invisible are now visible in greyish tone on the object.
Fingerprint matching was traditionally done manually, but this has been revolutionised by computer technology. The FBI-NCIC classification system and other techniques known as the Henry Fraction assigns numerical values to overall patterns on an entire set of ten prints. This allows the coding and filing of tens of millions of prints in an orderly manner.
TYRE PRINTS:
When someone walks or runs, or drives a vehicle, over soil, impressions are left in the ground. A frame is built around the print or track, a suitable casting material is poured in and allowed to dry, and then the cast removed and photographed. As shoes and tyres are used, individual characteristics such as nicks, cuts, and wear patterns develop. These characteristics may show up in prints and impressions and can be compared with a suspect's shoes or tyres.
Through the skilful combination of tracking and footwear impressions, it is often possible to recreate the events leading up to, those occurring during, and those occurring after the crime.
Black and white film is normally used to photograph footprints, unless the impression is in blood, and oblique light is shone onto the footprint. It is usual to take a series of photographs, each time varying the position of the light source, and a scale should be added to the scene. If the surface is light, the print may be highlighted using aerosol paint.
If the footprint is made in a soft material such as soil, a cast is made.
When footprints appear on a porous material like paper or cardboard, application of a low adhesive gelatine layer lifts the prints, which can be taken away for photography and closer analysis. Sometimes, the application of fingerprint powders or electrostatic powders, or use of appropriate lighting reveals latent prints, and black, white or transparent lifters are used.
Footprint impressions from casts and/or by photography will give investigators information about:
- the number of criminals.
- points of entry and exit.
- positions of suspect(s), victim(s) and witness(es).
- direction(s) of movement/travel and pathway(s) through the crime scene.
- time period, from short-lived impressions in frost, snow, dew.
- sequence and manner (walking, running, limping, staggering) in which the impressions were created.
- links between crime scenes, e.g. the same criminals committing several crimes in one evening.
- the type, size and areas of specific wear on the shoes.
Certain seasons or weather conditions lend themselves to the creation of footprint impressions than others. Soil trapped in soles can also give useful leads, such as soil pH, specific minerals or heavy metals in the soil, the presence of seeds or pollen grains.
Car tyre tracks and other dimensions can give information such as the make of tyre, degree of wear to, or specific marks on, individual tyres, and at least indications as to the make of car
When the track is found, the forensic will build a small wall around the print. This will keep the mould in. Then He/She fills the area with a plaster mix. This then hardens which creates an accurate mould of the track.
The tyre track is compared with that of known tyres or the suspect’s vehicle.
A few methods are available to record tyre test impressions that accurately capture the tread pattern, design, individual characteristics and wear characteristics. These involve inking or greasing the tyre and rolling onto brown or white paper or board, or developing the impression using black magnetic fingerprint powder.
Databases of car tyres are available in Europe and North America.
GLASS:
Glass is found in many types of cases. Like paint, it is often involved in burglaries and hit-and-runs. Glass fragments easily embed in shoes, hair and clothing of people involved in the breakage of glass. Sometimes glass fragments can be reconstructed to yield evidence. Reconstruction.
It is best to take a representative sample of the glass - this could be the four corners of a broken window, or all the glass available if the glass broken is not a window. If more than one type of glass is broken, collect representative samples of each different type.
Most glass analyses consist of comparing the refractive indices, elemental compositions and densities of two or more samples.
The forensic scientist will first of all assess the physical characteristics of the glass:
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Refractive index. This is a measure of how much the light is bent, or refracted, as it passes through the glass. If a colourless piece of glass is put into water, you can still see it because the water and glass have different refractive indices. The refractive index of glass does not vary significantly with temperature, but those of liquids do. If a piece of glass is placed in a liquid which is then heated, at some point the refractive indices will be identical and you will no longer be able to see the piece of glass. If the two pieces of glass – one the suspect and one from the scene of crime, have identical refractive indices, then they are from the same source. Nowadays, refractive index methods are semi-automatic – the GRIM2 instrument measures the refractive index of glass fragments by reference to calibrated immersion oils and automatically identifies the glass.
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Elemental composition. The elements investigated are usually sodium, magnesium, aluminum, silicon, potassium, calcium, barium and iron.
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Density measurements. The density of glass can be measured by flotation measurements, though this technique is rarely used these days.
HAIR:
Hair is made from a protein called keratin, and is found on the skin of mammals. Each species of animal possesses hair of characteristic length, colour, shape, root appearance, and internal microscopic features that distinguish it from another. Considerable variability also exists in the types of hairs that are found on the body of an animal. In humans (and other mammals), hairs found on the head, pubic region, arms, legs and other body areas have characteristics that can determine their origin.
Because hairs may be transferred during physical contact, their presence can associate a suspect to a victim or a suspect/victim to a crime scene. The types of hair recovered and the condition and number of hairs found all impact on their value as evidence in a criminal investigation.
Since hair evidence is generally difficult to handle because of it's size, care must be taken to protect evidence from loss or contamination.
Several methods are used to detect hair evidence - visual searches, searches using alternative light sources, and searches using additional magnification. Evidence should be recovered using the least intrusive technique practical - this includes picking, taping, scraping, combing or vacuuming.
Comparison of the microscopic characteristics of hairs from the scene of crime with known hair samples helps determine whether a transfer may have occurred.
If a hair comparison with a suspect is required, it is absolutely necessary that an adequate known sample be submitted this ranges from 25-30, pulled from the area of the body that the questioned hair is thought to have come from.
The examination of human hairs in the forensic laboratory is conducted using a light microscope – the questioned and known hairs are examined with the comparison microscope, two light microscopes connected with an optical bridge. The range of magnification used is approximately x40 to x400.
Similarities (or differences) between hair found at a crime scene and other samples is therefore a useful tool. It should be noted though that when a hair exhibits the same microscopic characteristics as hairs in a known hair sample, and a perfect match would be rare, it cannot give absolute identification, merely the basis for a strong association. A qualifying statement must added to the forensic scientist’s report.
PAINT:
Paint chips and scrapings may be left in the clothing of a hit-and-run victim or transferred to or from a car that has been hit by the hit-and-run vehicle. Paint chips or scrapings from building may also be in the clothing or on the tools of a burglar.
When paint samples are collected, it should be done so as to obtain a paint sample with all the layers of paint present. It is sometimes more desirable to submit an easily removed item, for instance the trim or moulding from a vehicle, to the laboratory.
Depending on the amount of sample obtained, paints can be analysed to determine their pigments and the specific type of paint - it is sometimes possible to find out the make, model and year of a vehicle in this way. Most important, however, is the comparison of a paint chip or scraping to a known sample coming from the suspected source vehicle or building - the paint layers obtained when several coats of paint are applied to woodwork on buildings over a number of years yield valuable forensic information when examined with a microscope.
Detailed analyses of paint composition can be carried out using mass spectrometry.
PLASTICS:
Samples of plastics at crime scenes can yield valuable information.
Standard forensic procedures apply to the collection of evidence, but samples of plastics can easily be removed surreptitiously by a rub of sandpaper or emery paper, and then analysis in the laboratory. Chemists at a least one major car manufacturer in the UK are known to obtain information about plastics used in their competitors’ models using this method!
Samples of the plastic - large samples, or those on sandpaper - can be analysed using infra-red spectroscopy. Observation of stress patterns using polarised light, for instance for identifying specific batches of plastics to provide a match, is also a useful technique if illuminated with polarised light, interference colours arising from stressed regions in materials can be easily observed.
POLLEN:
The pollen of most plants is highly sculptured when seen with high power light microscopy or scanning electron microscopy. The term forensic palynology refers to the use of pollen and spore evidence in legal cases. Forensic palynologists try to match pollen found in a known geographical location with pollen in a forensic sample. They also take into consideration what pollen types are released in various seasons, and how it is dispersed (pollen is usually transferred by wind, water, insects and other animals such as hummingbirds, bats, lizards, etc.). In some plants, pollen production is high, e.g. 70 000 pollen grains per anther in a single Cannabis plant, but in some with highly specialised pollen transfer, is very low, making palynology an extremely useful tool.
Samples which may yield pollen grains are collected using conventional forensic techniques.
Scanning electron microscopy will reveal the detailed structure of pollen grains in samples, so that species may be identified and compared with those on suspect’s possessions. Pollen grain evidence, because of the seasonality of the grains, has also been used to eliminate suspects. Analysis by a specialist palynologist is however essential.
If any clothing is found at the scene, it is possible that it could have body tissue on it. This means the forensic must be extremely careful in how he handles it.Clothing or shoes should be dried and then placed in individual paper bags. Known soil samples should be collected at the point of suspected origin, then two more - one sample on each side about one foot away and another sample on each side about ten feet away.
These samples should be taken from approximately the same depth as the questioned sample – if a shoe print is 6 mm deep, it is pointless to sample deeper than this.
SOIL:
Useful forensic information can be obtained from soil sedimentation analysis and pH measurement, but because of the similarity of the soils, this evidence should not be used on its own.
Soil sedimentation
- Label your soil/water mixture from the air content determination and set aside in the tray to settle for at least two days. The different types of particle settle out according to their density.
- Record accurately the depths of the layers of the different particles. The use of a measuring cylinder is deliberate!
- Label the different layers.
pH
- Place some soil, to the depth of 10 mm, in a test tube.
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Add some barium sulphate (about a spatula-full) to the test tube. Add distilled water (10 cm3) and shake thoroughly. The barium sulphate releases ions locked in the soil, so you will obtain an accurate pH reading.
- Allow to settle and add sufficient Universal Indicator solution to obtain a density of colour similar to that on the chart.
- Record the pH from the colour chart.
TEETH:
If the body of a victim is found a long while after the crime was committed, it is likely that it will be impossible to identify the body. This is common after an arson attack. The only part of the body that can survive this is the teeth. People have different patterns of teeth. Some people have bigger jaws and so on. There are around 200 ways of charting teeth. The “Universal system” assigns a number to each tooth – starting with the upper right (third) molar - 1 – and finishing with the lower right (third) molar – 32. Information is also recorded about the five visible surfaces of each tooth, so a detailed dental record, or odontogram, is built up. Conventional forensic methods are used to collect teeth from the scene of the crime, or charred or exhumed remains. Visual examination and photography are used to examine/record teeth marks at the scene of the crime. For successful identification of remains, post Morton and ante Morton records must be available. Odontograms can be compared with teeth marks from the scene of crime.
Teeth are also useful for determining a person’s age – dental growth is 4 micrometer’s per day and this growth is indicated by striations on the tooth. Because of this, it is possible to estimate the age of young people ± 20 days. After 25, identification becomes more difficult – teeth wear, the gums recede, the pulp cavities become smaller, etc, so the forensic odontologist can only give an approximate age - 42 months, at best.
Crime prevention:
There are many methods of preventing crime. Some are more efficient than others are. Things such as Vandal paint and CCTV are more of deterrents that do not actually stop the crime. They will help to catch the criminal afterwards. Other methods include Alarms, Security guards/ dogs, warning signs, fines, police and prison. There are many more ways of attempting to prevent crime. It is impossible to completely stop crime, as even with these Crime prevention techniques, people will still try to get away with criminal offences.