Crime is rapidly increasing in this day and age, however, thanks to the increasing technology we can now detect and prevent crime, using forensic techniques, which I shall detail in this essay.
Forensic Science
Crime is rapidly increasing in this day and age, however, thanks to the increasing technology we
can now detect and prevent crime, using forensic techniques, which I shall detail in this essay.
All contact leaves a trace; this is the basis of the policy taken by all forensic scientists, these
traces have to be collected, and then examined, however care and precautions (protective suits
and gloves etc) have to be taken to ensure that evidence or traces are not contaminated or
damaged. There are two approaches to collecting evidence; there is the cautious approach of all
visible areas and then the more vigorous search of concealed areas.
When scientists are trying to detect poisons or toxins in the body (e.g alcohol), the laboratory
methods they use are categorised as follows; physical tests, crystal tests, chemical spot tests,
spectrophotometric tests, chromatographic tests. If the toxin were known to be alcohol, the
collection and analysis would take place simultaneously, using a breathalyser test. A modern
breathalyser is the Lion Alcometer converts the chemical energy in ones breath to electrical
energy, an older method would be the "tube and bag", this would depend on the break down of
potassium dichromate by the alcohol in a drivers breath. However this is more of an on the spot
test, for drugs, other toxins and a more detailed analysis of alcohol, urine or blood tests will be
done. Gas chromatography will tell how much alcohol is in blood or urine. This is more accurate
than any other method, and can be used successfully in the court of law.
An important role of a forensic scientist in the event of arson is to establish the origins of the fire.
However, more volatile components will be lost to a degree, and so the scientist's jobs are
made harder. The most useful materials to be submitted for analysis are materials, which have
been relatively protected from the intense heat and/or are of porous nature near the suspected
point of origin. These recovered pieces of debris will be cleaned with acetone (propanone) to
dissolve accelerants and explosives. The most common technique used to analyse materials
from a suspected arson, is gas chromatography. However, this requires certain operating
temperatures at which some compounds will break down, if this is the case then high
performance liquid chromatography or infrared spectroscopy. In few cases, thin layer
chromatography will be used.
Ballistics is the study of firearms and bullets, at a crime scene forensic scientists compare the
bullets and cartridge cases, to try and identify the original firearm, they were fired from. The
forensic scientist determine the possible manufacture of a bullet by examining the rifling
impressions made on the surface of the fired bullet, the firing pin and breech face markings.
Castings and photographs of bullet holes also yield information. Test firings are often made
because the bullet changes shape on impact. If further analysis is needed swabs can be taken
from the person who was suspected to have fired the firearms, and then examined for traces of
lead, antinomy, and barium.
In crimes such as murder, rape, assault, robbery, and hit and run accidents, body fluids such as
blood are left behind. The examination made of these fluids, can prove or disprove a suspects
alibi, and/or eliminate suspects. DNA profiling can be done on any body fluid, and can also be
used to identify the father of a child. At the crime scene, photographs will be taken of all blood-
splattered objects, especially those that cannot be submitted for analysis. At the crime scene,
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lead, antinomy, and barium.
In crimes such as murder, rape, assault, robbery, and hit and run accidents, body fluids such as
blood are left behind. The examination made of these fluids, can prove or disprove a suspects
alibi, and/or eliminate suspects. DNA profiling can be done on any body fluid, and can also be
used to identify the father of a child. At the crime scene, photographs will be taken of all blood-
splattered objects, especially those that cannot be submitted for analysis. At the crime scene,
information can be taken from the size, shape and distribution of blood splatters at the scene. All
wet stains are air-dried first and packaged in separate paper bags, forensic experts wear
different gloves when for each bloodstain, and to ensure that cross contamination does not
happen. Sometimes samples will be taken from a suspect to compare with the samples from the
crime scene. Many analysis are made at the forensic lab, the first is to identify what the
substance is, blood has many different appearances depending on how long it has been there,
the weather and many other factors. After that tests are carried out to determine the animal
species origin, and blood type.
With other body fluids, such as saliva, and semen, conventional techniques are used to analyse
it, e.g. comparison to medical records. DNA analysis gives an extremely high power of
discrimination. DNA profiles are maintained in a computer database based in Birmingham it has
00 000 samples from crime scenes and 1 000 000 connected to crimes or being investigated.
Private laboratories also carry out DNA analyses in paternity cases. In this event the Childs
DNA and the mothers DNA will be compared to that of the fathers.
In the event of a forgery, documents will be photographed, and examined, if the forensic
scientist believes a forgery has taken place the follow these procedures. Identification of
signatures and handwriting - comparison using a microscope - identification of typewriters,
photocopies and computer printers - individual typewriters leave characteristics on the paper -
identification and deciphering of indented writing - a UV lamp would be used to reveal the
indent - and comparisons of inks and papers - inks are analysed for there pigments and the age
of the ink, the new Video Spectral Comparator 2000 technique is capable of detailed analysis
of both papers and inks.
In the event of an explosion, the forensic scientist will search and analyse any debris or soil that
is found close to the point of detonation in an attempt to find residue from the explosive.
Examination of accessories such as blasting caps, wires, batteries, fuses, containers and boxes
makes it possible to identify the manufacturer and any unusual odours are noted. There are two
types of explosives, low order explosives tend to eject the material rather than shatter, and they
produce large chunks of debris. High order explosives shatter and fragment material, if this was
the explosive used there will be much evidence of impact by fragments from shattered objects
effectively converted into small, high-velocity missiles. Determination of the type of explosion
can usually be done at the scene of the crime, debris that is taken away from the site is cleaned
with acetone (propanone) and then a form of chromatography is carried out usually gas
chromatography, much like in the event of an arson.
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. As a general guide, natural fibres tend to have a
rough and irregular appearance, while man-made fibres are longer and smoother. 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. If the fibre is a colourless fibre, like polyester, melting point and
refractive index determinations might be used. For man made fibres, analytical chemical
techniques. However, once it is found that the sample from the crime scene matches the sample
from the suspect, the reliability has to be assessed, e.g. if the garment the fibre came from was
from a chain store, it would have to be taken in conjunction with other evidence.
One of the most important discoveries in the history of forensic science was the discovery that
no two people, not even twins, have the same fingerprints. Since this discovery, rules of
classification have been layed down, (Sir Francis Galton identified 3 basic patterns - arches,
loops and whorls) and crime detection has soared. Fingerprint evidence is very fragile and must
be collected and analysed with care, there are 5 different methods that can be used to collect
latent fingerprints. The first is dusting, this method is best used on non-porous surfaces, it
involves powder being sprinkled over the place where the fingerprint is suspected to be, the
powder will stick to the sweat and oil, and the fingerprint is revealed. The excess dust is then
brushed off before the fingerprint is either photographed or lifted using sellotape. For porous
surfaces, iodine fuming may be used, this method produces a yellow-brown non-permanent
print which must be photographed, by exposing the material to iodine vapour, which reacts to
the sebum. The ninhyndrin spray, can be used to reveal fingerprints on objects like books or
paper, that are over 30 years old. Silver nitrate can be sprayed onto a surface, or applied with a
brush or swab, then if allowed to dry and put under ultra violet light, the fingerprint is revealed.
It will need to be photographed as the print will dissapear after a short time. The last method of
revealing fingerprints is superglue fuming, the superglue vapour reacts with the water in a print,
the object with the print will have to be placed in a sealed tank to do carry out this method, as
the fumes are dangerous to humans. This method will show the fingerprints in a greyish tone.
Once fingerprints have been collected they will be compared with the suspects, traditionally this
was done manually, but it has now been revolutionised by computer technology. All records of
prints are kept in a database.
Footprints and tyreprints are left behind when someone travels over soil, the first thing a forensic
expert would do, would be to make a cast of the print, this is done by first building a wall
around the print and then pouring plaster or another casting material into the frame. This is
allowed to dry and then the cast is removed and examined, photographs of the original print are
also taken. 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. Footprint and tyre print impressions can yield the following information;
- 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
- the make of the tyre from the tread pattern and design
- indications as to what make the car was
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. Prints will be compared with the
suspects sole or vehicle and/or other known tyres or soles. There are databases of car tyres in
North America and Europe.
Glass is found in many types of cases, particulary robbery and hit and runs. Glass fragments
could be imbeded in the hair, clothes or shoes of the people involved in the breakage of glass.
Glass is easily collected, but it is best to take representative samples e.g. the four corners of a
broken window. Representative samples of all types of glass need to be taken if more than one
type of glass has been broken. Glass analysis mainly consists of the comaparison of 2 samples'
refractive indices, elemental compositions and densities. Refractive index is the amount that light
bends or refracts as it passes through glass, if both samples (the suspects and the one from the
scene of the crime) refractive indices match, then both pieces of glass came from the same
source. The new GRIM2 instrument measures the refractive index by refrence to calibrated
immersion oils and automatically identifies the glass. The elemental composition is the
identification of the elements in the glass, these usually include sodium, magnesium, aluminum,
silicon, potassium, calcium, barium and iron. The measuring of two samples densities is rarely
used these days, but it is usually found by flotation measurements.
Hair may be transferred during any physical contact, so they could link the suspect to a victim or
the suspect/victime to a crime scene, when collecting hair evidence forensic experts will do the
same as when collecting other fibres. Hair evidence from the scene of a crime is usually
compared to other known hair samples, this will be conducted using light and comparison
microscopes.
Much like glass, paint is left behind in cases such as robberies and hit and runs. When paint is
collect samples of all layers need to be taken, sometimes it is easier to just submit a whole
object or item in for analysis. 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. Samples from a crime scene are also compared to samples from the suspected source.
When collecting plastic evidence at the scene of a crime, standard forensic procedures are
followed, however, rubbing the plastic with sand paper or emery paper, easily removes a small
sample of plastic which can be sent to the lab for analysis. Analysis of plastic is either done using
infra-red spectroscopy or the observation of stress patterns using polarised light.
Pollen particles are highly structured when viewed under high light microscopy or electron
microscopy. When analysing pollen, a sample from a known geographical location is compared
to a sample from the suspected source. However, factors have to be taken into consideration
e.g. how the pollen is dispersed, what pollens are released in which seasons.
Soil is found frequently on soles of shoes, clothing, wheel wells of vehicles etc. and most soil
analysis consists of comparing a suspect sample with the sample from the scene of the crime, the
factors monitered would be soil sedimentation analysis, pH measurements, mineral contenst,
colour and density, further comparison can be made by detecting any pesticides or herbicides
present.
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(odontogram) is built up.
Durability of teeth makes them an ideal means of identification for the forensic scientist as they
are often the only means of identification after fires. Features of teeth can identify the criminal
when bite marks are left at the scene of the crime. For successful identification of remains, post
mortem and ante mortem records must be available. Teeth can also yield information a persons
age.
Once forensic experts have carried out as much analysis as possible they must construct a
report that is admissable in the court of law, they sometimes make mistakes, and they evidence
they come up with is not always 100% accurate, however, it can help make or break a case.
