Locard Exchange Principle

Trace Evidence. Trace evidence (23) refers to minute, sometimes microscopic material found during the examination of a crime scene or a victim s or suspect s clothing (see Trace AND residue analysis). Trace evidence often helps poHce investigators (24) develop connections between suspect and victim and the crime scene. The theory behind trace evidence was first articulated by a French forensic scientist the Locard Exchange Principle notes that it is not possible to enter a location, such as a room, without changing the environment. An individual brings trace materials into the area and takes trace materials away. The challenge to the forensic scientist is to locate, collect, preserve, and characterize the trace evidence. 

Local flux-density profile, 23 816 Localized molecular orbital (LMO) calculations, 10 633 Locally weighted regression, 6 53 Local oscillator (LO), 23 142, 143 Local toxicity, 25 202 Locard Exchange Principle, 12 99 Lochett, W., 11 8... 

In 1910 the French scientist Edmond Locard, inspired by the Adventures of Sherlock Holmes, postulated the fundamental principle on which forensic science and trace evidence is based, namely, The Locard Exchange Principle (Chisum and Turvey 2000). When two things come into contact, physical components can be exchanged. For example, the exchange can take the... 

Locard in 1920 expressed the fundamental axiom, sometimes referred to the Locard exchange principle , that, in essence, every contact leaves a trace any person committing a crime leaves something at the scene that was not there before and carries away traces that were not associated with him when he arrived. When an item is submitted to the laboratory for analysis, the usual questions are ... 

Hair is an important type of physical evidence that frequently occurs in criminal and civil cases. For example, human head and pubic hairs may be exchanged between the perpetrator and victim in a case of sexual assault (an example of the Locard exchange principle (DeForest et al., 1983)). Hairs may also be found embedded in upholstery or decorative plastics in the interior of automobiles following automobile accidents (Masakowski et al., 1986). 

Chisum, W. and Turvey, B. (2000). Evidence dynamics Locard s exchange principle and crime reconstruction. /. Behavioral Profiling 1,1-15. 

The field of forensic microscopy is based upon Edmond Locard s Exchange Principle, which states that when two objects come into contact, a transfer of material will result. Although the amount of material that is transferred in a contact may be minute, microscopical examination can often reveal a great amount of information regarding the materials that came into contact and the way in which they made contact. This article illustrates the way in which forensic microscopy can capitalize on this transfer of... 

Sir Arthur Conan Doyle is believed by many to have first popularized the application of forensic analysis through his newspaper serials originally pubhshed in 1887 featuring the fictional character Sherlock Holmes. This work is thought to have inspired many of the early forensic scientists. One of these was Frenchman Edmond Locard, who proposed that when two objects come into contact with one another, a cross-transfer of evidence occurs (1,2). This is the basis of Locard s Exchange Principle and is the foundation of how we can often use physical evidence to link or at least associate a suspect to a crime scene or a victim. Depending on the nature of the evidence, a wide range of analytical methods are used in forensic casework. 

Fibers identical in all respects to those found on the victim s body were discovered in the truck and workshop of the suspect. Single-layered paint chips in a wide variety of colors and metal particles and spheres were also found in the suspect s workshop. The finding of particles identical to those from the suspect s environment on the victim was a practical example of Locard s Exchange Principle. Since the girl did not have these particles on her clothing when she left the... 

So far, the discussion has focused on the wealth of tools available for fiber aruilysis. However, mention must be made of some of the practical sampling issues that arise. Fibers are ubiquitous and are easily transferred as per Locard s exchange principle. Along with dust, fibers are the most common class of transfer and trace evidence, and this commonality itself creates caveats that affect any fiber analysis. In addition, modem mass-production techniques are purposely designed to manufacture fibers that have minimal variation. This is good for the consumer, but bad for tiie forensic scientist, given that evidence is classified and distinguished on the basis of differences. Mass-production techniques have made it harder to find those differences which are critical to differentiation. 

The analysis of many classes of materials is undertaken with the purpose of discovering the chemical and physical history of the object. This is certainly the case in forensic analysis where substances collected from a crime scene can provide vital information that may incriminate suspected criminals. The exchange principle enunciated by Edmund Locard (Thornton, 1997) is also applicable to fibers in the sense that every stage in the synthesis or processing of the fibers or filaments, every thermal or mechanical treatment and every subsequent contact with chemicals leaves an indelible mark on the material. The challenge is to detect, characterize, and correctly interpret the information. Thermal analysis provides a set of tools that, effectively applied, can provide a wealth of information from minute samples. 

In the early 1900s Edmond Locard began to develop forensic science as it is known today. In 1910 he persuaded the Lyon Police Department to give him rooms and assistance to start the first police laboratory. It was Locard s belief that when a criminal came into contact with an object or person that a cross-transfer of evidence occurred - this is known as Locard s exchange principle. Thus every criminal could be linked to a crime scene by particles transferred. 

The function of the forensic scientist today is largely based around Locard s exchange principle. The expertise available in an operational forensic science laboratory covers a range of disciplines and uses a number of scientific techniques. Forensic scientists must therefore be skilled in many scientific areas. They must also be aware of the demands and constraints of the legal system, so that the results of analysis satisfy the criteria of admissibility as evidence that have been established by the courts. 

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