Evidence Dynamics: Locard's Exchange Principle & Crime Reconstruction

"Evidence Dynamics: Locard's Exchange Principle & Crime Reconstruction"

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Of all responsibilities shouldered by the forensic scientist, the reconstruction of the circumstances and behaviors involved in a crime is one of the most important. In conjunction with agreeable witness accounts, a crime reconstruction may be a powerful instrument of corroboration. In the face of conflicted witness accounts, it may provide an objective view that points to one possibility over another. In the absence of witness accounts, it may be used to investigate and establish the actions that occurred at the scene of a crime. The role that crime reconstruction can play investigatively and legally should never be underestimated.

Because of the varied evidence and circumstances involved, the ability to reconstruct crime requires broad forensic knowledge, an objective if not conservative disposition towards the examination and interpretation of evidence, and what the fictional Dr. Watson of Sherlock Holmes fame referred to as a "peculiar facility for deduction." [9]

Despite its importance to investigative and legal venues, crime reconstruction is often performed inappropriately by the unknowledgeable and overconfident. This includes those with little knowledge of, or training in, the peculiarities of physical evidence and the forensic sciences. Those testifying as experts in the area of crime reconstruction routinely cite as a premise, for otherwise unproven opinions, the sum of their education, training, and experience. It may be the case that this is offered in the place of facts from the case file. This practice is regarded as illegitimate for a forensic examiner. "Experience should not make the expert less responsible, but rather more responsible for justifying an opinion with defensible scientific facts." [12]

Conclusions regarding the circumstances and behaviors elicited from the physical evidence related to a crime can infrequently be housed within the confines of absolute certainty. It is often an intensive process with imprecise results containing evidentiary holes, sequential gaps, and alternate possibilities. This does not suggest that crime reconstruction efforts lack investigative or legal utility. The utility of crime reconstruction is by no means bound to any predisposition for certainty. Rather, its utility is more often found in establishing the general circumstances of a crime, demonstrating links between victims, suspects, and offenders, corroboration of witness statements, providing investigative leads, and identifying potential suspects. [8]

Further still, it is often the case that what the physical evidence excludes, fails to establish, or equivocates, is actually of great investigative and legal importance. Forensic analysis in general, and crime reconstruction in particular, is concerned with those conclusions that can be logically drawn from the evidence, as well as with those that cannot. As such, the consideration of both the strengths and limitations of available physical evidence are an important part of crime reconstruction. It is with these considerations in mind that we begin our discussion of the relationship between Locard's Exchange Principle, Crime Reconstruction, Evidence Dynamics and their implications to forensic examinations.

The Development of Locard's Exchange Principle

Alphonse Bertillon developed one of the first scientific systems of documenting personal identification in Paris in the late 1800s [3, 11]. In 1879, Msr. Bertillon began his career when he was appointed clerk in the Premier Bureau of the Prefecture of Police [10]. The sheer volume of the files required organization. He used the measurement system that his father, a physical anthropologist, used to organize skeletal material. Bertillon's genius was in adapting this method to living persons and establishing a record system. The method referred to ultimately as Bertillonage used the relatively simple procedure of taking a series of body measurements, noting other physical characteristics, and placing this information on a single identification card in a police file [3]. As the method developed he started adding photographs of the individual to the files. Bertillonage was a significant advancement in terms of providing a useful database of criminals for criminal investigators.

Bertillon was motivated to develop his methods not only by the desire to assist in the tracking of criminals and their behavior, but also by a personal belief that everything that "lived and moved under heaven" was somehow unique [10]. His was something of a radical notion in criminal investigation at the time: that science and logic should be used to investigate and solve crime. As Msr. Bertillon's biographer stated:

The methods of the French police in that year of grace 1879 had changed very little in principle from those initiated by that criminal turned policeman, the brilliant and unscrupulous [Eugene] Vidocq. They consisted in the liberal use of the police informer, and agent provocateur. [10]

Bertillonage was employed to identify criminals by law enforcement for at least two decades, until it was replaced by the use of fingerprints. In 1891, Dr. Hans Gross, an Austrian Magistrate and Professor of Criminology, made the following observation, "The advantages of finger-prints over the Bertillon system have become so well established that the latter can with perfect safety be dispensed with altogether as unnecessary for the purposes of identification."[5]

However, Bertillonage was not the limit of Msr. Bertillon's contribution to the forensic sciences, nor was it his most significant. His dedication to precise measurements and the use of photography led to a combination of the two practices beyond criminal identification. Bertillon assisted in the development and practice of forensic photography by introducing a measuring scale with the persons and objects of evidence that he photographed [10]. The usefulness of this practice soon became apparent. He was routinely sent out with investigators to document crime scenes. He would photograph the bodies of victims, their relationship to significant items of evidence in the scene, as well as the position, size, nature and extent of other physical evidence including footprints, stains, toolmarks, and points of entry [10]. Until the development of this practice, criminal investigators and the courts relied upon sketches and notes of varying precision for their understanding of the context of a crime. That is, if any record were made of a crime scene at all.

Bertillon also instructed and influenced several students, including Dr. Edmond Locard, whose work formed the