Interpreting Evidence
Evaluating Forensic Science in the Courtroom
Bernard Robertson, G. A. Vignaux, Charles E. H. Berger
- English
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Interpreting Evidence
Evaluating Forensic Science in the Courtroom
Bernard Robertson, G. A. Vignaux, Charles E. H. Berger
Ă propos de ce livre
This book explains the correct logical approach to analysis of forensic scientific evidence. The focus is on general methods of analysis applicable to all forms of evidence. It starts by explaining the general principles and then applies them to issues in DNA and other important forms of scientific evidence as examples. Like the first edition, the book analyses real legal cases and judgments rather than hypothetical examples and shows how the problems perceived in those cases would have been solved by a correct logical approach. The book is written to be understood both by forensic scientists preparing their evidence and by lawyers and judges who have to deal with it. The analysis is tied back both to basic scientific principles and to the principles of the law of evidence. This book will also be essential reading for law students taking evidence or forensic science papers and science students studying the application of their scientific specialisation to forensic questions.
Foire aux questions
Informations
Chapter 1
Introduction
- that a particular person was at a given place at a given time;
- that a particular person carried out an activity, such as signing a cheque or breaking a window;
- that something was done with a particular instrument, for example, a door was forced with a particular tool, a shot fired from a particular weapon, or a call made from a particular telephone;
- a relationship between two people, for example, in paternity disputes and incest or immigration cases.
1.1 Three âprinciplesâ
- Locard's âPrincipleâ: A perpetrator will either leave marks or traces on the crime scene, or carry traces from the crime scene. This is often misquoted as âevery contact leaves a traceâ but Locard never actually claimed this. Edmond Locard (1877â1966) was a French forensic scientist. He proposed that we should always consider whether traces of the victim or crime scene can be found on the accused and whether traces of the accused can be found on the crime scene or victim. After an assault, for example, we might find skin and blood under a deceased's fingernails and infer that they come from the attacker. We might arrest a suspect on the basis of other evidence and find, on him or his clothing, fibres which might come from the deceased's clothes, blood which might come from the deceased or soil and plant material which might come from the scene.
- âPrincipleâ of individuality: Two objects may be indistinguishable but no two objects are identical.2 The combination of these two ideas together might seem to have enormous potential value to the forensic scientist. If every contact provides ample opportunity for the transfer of traces, and every trace is different that seems to be cause for optimism. However, if no two objects are identical, then, for example, no two fingerprint impressions will be identical even if they are taken from the same finger; no two samples of handwriting by the same author will be identical. The question is whether two marks have the same source, and how much our observations help us in answering that question.We describe these two statements as proposed principles rather than laws because neither meets the standard definition of a law of science. The philosopher Karl R. Popper (1902â1994) said that for a law to be regarded as scientific it must be potentially falsifiable, that is, it must be possible, at least in theory, to design an experiment which would disprove it.3
- It seems to be impossible to design an experiment to refute the first of these principles. If an experiment fails to find an impression after two objects have been in contact, it may be that all that is revealed is the limitations of the detection process. The proposed principle that no two objects are identical does not require proof, since two objects that would be identical in every way would â by definition â be one object. Unfortunately, it does not follow from the uniqueness of every object that we can correctly point out its unique source.
- Individualisation âPrincipleâ: If enough similarities are seen between two objects to exclude the possibility of coincidence, then those objects must have come from the same source.
The principles which underlie all proof by comparison of handwritings are very simple, and, when distinctly enunciated, appear to be self-evident. To prove that two documents were written by the same hand, coincidences must be shown to exist in them which cannot be accidental.4When any two items have characteristics in common of such number and significance as to preclude their simultaneous occurrence by chance, and there are no inexplicable differences, then it may be concluded that they are the same, or from the same source.5âŠwe look for unique characteristics in the items under examination. If we find a sufficient number of characteristics to preclude the possibility or probability of their having occurred by coincidence in two different objects, we are able to form a conclusion of individualization. It's as simple as that.6