Locards law has a huge impact on the way evidence is collected at a crime scene it was locards belief that when a criminal came in contact with an object or person a cross transfer of evidence occurred… and that every criminal can be connected to a crime by dust particles carried from the crime scene1 There are a number of methods used to connect a person to a scene. Some of these methods include glass fragment analysis, fingerprint and footwear recovery, DNA analysis and hair and fibre analysis.
There are also technological methods that can be used to link a person to a crime for example CCTV cameras can be used to identify a person's involvement. DNA DNA has the highest priority when collecting evidence due to the fact that no two people have the same DNA code except in the case of identical twins. Biological evidence can exist in the form of blood and other body fluids such as spittle, semen, vaginal secretions, or any other… DNA source. 2 The DNA code is used to differentiate the uniqueness between two people, as it contains genetic information that corresponds to the parent.
The technique most commonly used to analyse DNA is called restriction fragment length polymorphism (RFLP). This technique looks at certain regions of DNA which consist of repeated sequences of units known as variable numbers of tandem repeats (VNTR's) the exact number of these consecutively repeated sequences varies from individual to individual and therefore the length of the VNTR region varies. It is for this reason that VNTR's can be used as markers for human identification3 This can be used to either eliminate or identify a person's involvement in an offence.
The advantages of DNA evidence include accuracy as the chance of finding two people… with the same DNA profile is currently estimated at between 100million to 1 and 30billion to one4 Another advantage is that it is durable, as under good conditions DNA can last for thousands of years, so it can be obtained from skeletal remains. Two disadvantages of DNA testing are that it is 50 to 100 times more expensive than other tests and it takes a long time to process and get the results. In relation to the case DNA evidence could be found from the blood on the broken glass, the cigarette ends, the balaclava and the glass of milk in the kitchen.
Fingerprints Fingerprints are one of the best methods of identification. They are made up of a number of tiny ridges which create a pattern. These patterns are what make fingerprints unique. There are three different types of fingerprints that can be found at a crime scene. Plastic prints are found on surfaces such as new paint or grease, visible prints are found when a person has put their hands in a substance such as blood then touched a clean surface and latent prints are invisible, as they are formed from perspiration and oil on the fingertips. They are found on smooth surfaces such as glass or paper.
Fingerprints can either be photographed or lifted depending on the surface where they are found. If the object is dark, a light powder is used, if it is light or white a black powder is used5 Fingerprint identification… has been used for over 100years. The human friction ridges are unchanging throughout life and there has not been a duplication of any two sets of prints. 6 Due to the fact that no two people have the same fingerprints it can be an extremely useful way to determine a person's involvement in a crime. In some cases if a persons fingerprint is not found at a scene it does not always mean that they were not involved.
The main disadvantage is that if a person wears gloves or has no, or little, fingerprint left due to fire damage there will not be a fingerprint left behind at the scene. In relation to the case fingerprints could be found on the broken glass, cupboards, door handle and the glass of milk. Hair and Fibre Hairs and fibres are found at a crime scene where physical contact has taken place such as rape, traffic incident or assault. Hairs are small which means they are difficult to see. It needs to be determined whether the hair is human or animal, and then if it's human it needs to decide where on the body it came from.
'Hairs that have been bleached, dyed, straightened or otherwise treated7' have different characteristics which can determine where the hair came from such as whether it is male or female. They can also show the presence of head lice or fleas which can be used for comparison. If a hair is forcibly pulled out from the victims head there is the chance that the root is still attached which means its 'possible to determine the DNA type of an individual from sheath cells found on hair roots8' Sheath cells are only found on hairs that are pulled out, not those that have been cut or fallen out naturally.
The advantage of using hair as evidence is that if it has been pulled out then DNA can be taken from the root to be compared to the suspects DNA, but the disadvantage is that if there is no root on the hair then its weaker as evidence due to the fact that two people can have similar hair and it cannot be determined where the hair came from. 'Fibres… are often overlooked by investigators because of their extremely small size9' Fibres can be transferred from contact between two peoples clothing as well as from items such as blankets and carpets.
They can be tape lifted, or picked up using tweezers and being put onto a microscopic slide. The tests done in the laboratory can determine the type of fibre that was found as well as if it matches or is similar to the control sample taken from the suspect. The advantage of using fibres as evidence means that it can narrow down suspects and possible items found at the scene, but the disadvantage is that because a number of items are now mass produced it means it is not possible to determine if the sample came from the questioned garment. Footwear
Shoes are a valuable item of evidence as when they are examined they can have dust, soil and bloodstains on them which can link them back to a crime scene. They can be found almost anywhere for example a dust print can be found on a piece of paper, or a bloody print can be found on carpet if a person has stood in blood. The most valuable details on a footprint are signs of wear and characteristics fittings. If a footwear impression is found it needs to be preserved as evidence. 'Preservation should be done by both photographing and casting or, in the case of dust prints, by lifting'10
The advantage of using footprints as evidence is that if the shoe is well worn then this produces characteristics that can be examined. These characteristics are caused by certain variables such as how the person walks, where the person has been among other things. The disadvantage of using footprints as evidence is that if the print is not lifted correctly then some of that evidence can be lost in transportation, so then the photograph can then be used as 'a backup procedure that is available to the examiner if the impression is damaged before reaching the crime lab'11
In this case footwear impressions were found on the kitchen floor as muddy footprints were left. Glass Glass can be useful as evidence in a variety of cases such as a hit-and-run. Glass can be from a variety of sources such as headlamps, windshield, reading glasses and windows of houses. 'Burglaries frequently involve window glass; and bottle glass is sometimes found in assault cases'12 Examining the glass found at a scene can give information about whether the pane was broken from the inside or outside, as well as what projectile was used such as a bullet from a firearm or a rock from a nearby garden.
'Broken glass may yield information about the direction and speed of a projectile and… sequence of events'13 There are two types of fractures that will be found on pieces of glass at a scene. 'These fractures are called radical and concentric fractures'14 Radical fractures are cracks that start from the centre of the point of impact, and outwards in a star-shaped pattern. The advantage of using glass as evidence is that 'glass shards are almost impossible to clean up completely…
They adhere invisibly to almost any surface'15 so it is very likely to find glass shards on a suspect to link them to the scene. The disadvantage of using glass as evidence is that when glass is broken it can travel up to 3metres in distance so it is possible for a person who is not connected to the crime in anyway could have glass shards on them. In this case glass shards would be found outside the kitchen window.