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. Dr Edmund Locard, one of the founding fathers of forensic science stated that “every contact leaves a trace”, this statement became commonly known as ‘Locards Exchange principal’. The statement in a broader sense means: every time an individual comes in contact with a place or another individual, something of that individual is left behind at the place, and something of that place is taken away with the individual. For example, if someone gives you a big hug and walks away, fibres from their clothes will be transferred on to your clothes and vice versa.

There are 2 types of forensic evidence that may be left at a crime scene, namely:

* Biological (DNA)

* Non – biological

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Biological evidence is evidence, which helps confirm the identity of the suspect, these are as follows:

* Blood

* Semen

* Saliva

* Urine

* Vomit

* Hair


DNA is a big step for science. A persons DNA (de-oxyribonucleic acid) can be found from a single strand of hair, skin under a murder victims nails or body fluids such as sweat, saliva, semen and blood. The chances of a sample of DNA being the same as another person, other than monozygotic twins is 1 in 24 million. This is why recent cases such as that of Sarah Payne rely so much on DNA samples found at the crime scene. In this case a single strand of Sarah’s hair was found on Roy Whitting’s sweatshirt and matching fibres from his were found on her shoe.

The method of extracting the DNA from the sample is a complex one. DNA must be extracted from the sample of body tissue or fluid. Some offences that are committed rely almost solely on forensic evidence such as that of rape. If semen is discovered and recognised as that of the suspect then that is nearly a conclusive result.

* The rape and murder case of Avril Dunn 1985 was solved 10 years later thanks to a new technique of DNA profiling. The police obtained semen samples from the men questioned at the time of the murder. The sample provided by Duncan Jackson matched the semen found on the victims clothing, which led to his conviction.

DNA profiling can be performed on any biological substance. It can also be used for the identification of bodies when samples from parents and/or children of the missing person are available.


Blood is of value in such crimes as murder, rape, assault, robbery, burglary and hit-and-run accidents. Blood evidence may aid an investigation by locating the crime scene, by identifying the weapon used, by proving or disproving a suspect’s alibi, and by eliminating suspects.

* Stains on clothes and fabrics: Any stain that is wet must first be air-dried. Each item is packaged separately in a paper bag, not plastic.

* Stains on surfaces: Body fluid stains can be swabbed using cotton buds dampened with distilled water. The cotton buds, along with control cotton buds – which have been used to swab a non-stained part of the surface – are air-dried before packaging separately in paper.

First an analysis must be carried out on a stain to determine whether it is blood or not – the appearance of blood varies greatly depending on the age of the sample, the weather and other factors. It is also important to obtain sample blood from the accused. Important information can be obtained from the size, shape, and distribution of blood splatters at the scene.

* In the case of R v Silbermann1, the accused was convicted of murdering both his parents, following blood evidence found at his home as well as his fathers ceiling in Paris.

* In the case of R v Stockhill2, the blood patterns that were found at the scene of the crime, did not match the chain of events reported to the police by Stockhill (patterns did not demonstrate a stuggle), it was later found that his wounds were infact self inflicted, combined with other evidence it led to his conviction for murder and attempted murder.


In humans, 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.

Several methods are used to detect hair evidence – visual searches, searches using alternative light sources, and searches using additional magnification. Evidence is recovered using techniques that include picking, taping, scraping, combing or vacuuming.

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. Similarities (or differences) between hair found at a crime scene and other samples are therefore a useful tool.

* The Sarah Payne case (detailed above) involved strands of Sarah’s hair found on Roy Whitting.

Non – Biological evidence is trace evidence which the suspect has left at the scene of a crime or can link the suspect with the crime in question, these are as follows:

* Fibres

* Finger marks

* Tyre & Footwear marks

* Soil

* Paint

* Glass

* Firearms


Since the perpetrator of a crime may transfer fibres from his/her clothing to a victim, or vice versa, the subsequent identification of fibre type(s) comprising a target garment and the comparison of these with any suspect fibres, is a potentially invaluable method of demonstrating associations between individuals and/or places.

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. The Recovery techniques of fibres include picking, taping, scraping, or vacuuming.

When examining fibres, the forensic scientist may use a special microscope called a comparison microscope – 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 the samples from crime and suspect match, the probability of the suspect’s guilt then has to assessed and evidence will be used in conjunction with other evidence collected.

* In a case where a young boy was found dead3(strangled), fluid taken from the eye and potassium levels were examined to identify time of death. The only evidence that was found at the scene of the crime was an unusual piece of fibre (carpet), it was this fibre, which led a trail to the suspect and matching DNA evidence led to the conviction.

Finger marks

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. 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!

* 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.

* 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 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).

* 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.

* 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.

* In 1999 Mandy Powers, her two daughters & mother were all murdered. Bloodstains were found all over the house. Finger and palm marks were found and later traced and matched to David Morris, who was convicted for all three murders.


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 a building may also be in the clothing or on the tools of a burglar.

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 and examined using a microscope.

* A case in Bedfordshire involving a serial murderer was solved through the process of paint identification. At one of the crime scenes paint was found on a tree, which had been hit by a car. This resulted in a search that ended with in the arrest of Michael Farley, blood, fibre and a newly made evidence were also found in his possession, which led to his conviction.


Glass is found in many types of cases. Glass fragments can be easily embedded in shoes, hair and clothing of people involved in the breakage of glass.

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:

* Refractive index. This is a measure of how much the light is bent, or refracted, as it passes through the glass.

* Elemental composition. The elements investigated are usually sodium, magnesium, aluminium, silicon, potassium, calcium, barium and iron.

* Density measurements. The density of glass can be measured by flotation measurements, though this technique is rarely used these days.

* In a bank robbery case4, where the cashier was shot and killed through a glass divide, forensic experts had stated that there would some broken glass fragments that would have been embedded into the suspect’s clothes. The investigation led to a Michael George Wheller, experiments found glass fragments, which matched the glass in the bank, on items of clothing ; vehicle Wheller. Along with other evidence, such as the firearm, it led to his later conviction.


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. Furthermore, examination of the fired bullet will contain markings, which will be coherent to the markings inside the barrel of the gun; this is often compared to identify the weapon, which was used to fire the bullet. Test firings are often made because the bullet changes shape on impact.

* In a case that involved the shooting and killing of a father and son5, the bullets used were identified as coming from a firearm (Russian Gun) that was used in 16 other crime scenes.

Gunshot Residue

An individual can also be linked to a crime, which has involved the firing of a gun, by gunshot residue. Gunshot residue may escape from various openings in the firearm: from the space between the chamber and the barrel in revolvers, from the ejection ports of self-loading or automatic firearms and even from the trigger hole. In the field of forensic science, the detection of gunshot residue becomes important in two aspects of the investigation of a shooting incident: the determination of the range from which a shot was fired and as an aid in the identification of the shooter. The first involves the examination of powder patterns on the surfaces of targets, and the second involves the analysis of residues removed from the hands of a suspected shooter.

* In the R v Wheller 6 case (detailed above), gunshot residue was found on items of Whellers clothing and used as evidence.

Footwear ; Tyre Marks

When someone walks, runs, or drives a vehicle, over soil, impressions are left in the ground. 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.

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.

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, can give indications as to the make of car. 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.

* In a case that went to trial in Canada in 1948, two brothers, Donald and William Kett, were accused in a series of breaking and entering offences. After Donald was convicted, William claimed he was innocent and that the shoes that were matched back to the crime scenes belonged to his brother. However, the shoes were cut open and the marks inside compared to the feet of the two brothers. Based on this comparison, it was determined that William had worn the shoes and he was also convicted.

The future of criminal evidence will be an exciting one to watch. With the aid of the spectacular advances in science, evidence will continue to improve with the use of technology and provide more answers from physical evidence examinations to previously unresolved questions. As the technology changes, so, too will the quality of the profession. Laboratory accreditation, which began as a voluntary program, is now an essential criterion for an operational crime laboratory in the United Kingdom.


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