Forensic Science: A Very Short Introduction (Very Short Introductions) by Fraser Jim

Author:Fraser, Jim [Fraser, Jim]
Language: eng
Format: mobi, epub
Publisher: Oxford University Press
Published: 2010-02-24T16:00:00+00:00

Chapter 6

Prints and marks: more ways to identify people and things

Marks (or impressions) are caused by a pattern from one item being transferred to another. This could be a shoe mark, a finger mark, or, less obviously, the pattern of striations on a plastic bag made by a tool in the manufacturing process. Firing pins in guns (see Figure 11), as well as saws, tyres, screwdrivers, and feet can all leave marks that can be used to identify the general type of object that made them (a shoe, a tyre) and sometimes even the specific object. This chapter uses fingerprints and shoe marks to illustrate the general characteristics of marks evidence, the principles involved in their examination, and how the evidence is evaluated.

Fingerprints and shoe marks are the most important and frequently encountered evidence of this type. In the view of most marks examiners, identification of an object (or an individual by fingerprints) can be done unequivocally, that is, with 100% certainty. We have everyday experience of marks and have ourselves on occasions made such judgements: who muddied the kitchen floor - a small boy (a shoe mark) or a small dog (a paw mark)? Understanding the application of marks to the investigation of crime is an extension of this everyday experience. Less obvious is how such marks can be used in intelligence databases to analyse crime patterns, or determine if someone should be charged with possession of drugs or possession with intent to supply drugs.

Marks can be visible (patent) or invisible (latent) and require specialist optical, physical, or chemical techniques to visualize them. They can be made in a variety of substances: mud, blood, dust, sweat, soot - referred to as ‘negative’ marks; or by transferring a material to another surface - ‘positive’ marks. A shoe stepping into a pool of blood can leave a negative mark in the blood followed by positive marks on the floor walked upon.

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