safety of trace evidence

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SAFETY OF TRACE EVIDENCE

All of this serves to refocus attention on some of the consequences of

the entry of forensic science into the marketplace without there being

Trace and Contact Evidence 81

any system of personal accreditation and regulation of the profession

in place. Historically, defence lawyers have experienced difficulties in

identifying properly qualified forensic scientists to check the prosecu-

tions scientific findings from amongst all those who would claim to be

competent. But now this has been extended to the investigating and

prosecuting authorities themselves. Not only does it remain difficult

always to ensure that the work is properly checked, it may now be

difficult to ensure that it was properly done in the first place. In these

circumstances, it seems likely that quality and standards may be sacri-

ficed in the name of economy, and nobody should be surprised if trace

evidence remains very much in focus as a possible contributor to future

cases in which it is shown there has been a miscarriage of justice.

Against this background, lawyers should be cautious about forensic

science evidence in general and trace evidence in particular. If prose-

cuting, they should make sure that:

1. The work was done by a reputable forensic science laboratory.

2. The scientist concerned is aware of all the relevant circumstances

in the case.

3. The work has not been artificially shaped or curtailed through

lack of funds.

If defending, lawyers should.


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1. Never accept scientific evidence from whatever source at face value.

2. Always ensure that the scientist appointed is properly qualified

and experienced and has investigated in a primary sense many

cases of the same general type and not merely looked over the

shoulders of those who have.

3. Take a very robust line with legal aid authorities over funding

for the work and not be fobbed off with the requirement to take

the lowest estimate unless it can be established that the scientist

concerned knows what they are doing.

3.7 BIBLIOGRAPHY

C. Catling and J. Grayson, Identification of Vegetable Fibres, Chapman and Hall,

M. Grieve, Fibres and Forensic Science - New Ideas, Developments and Techniques in

R.C. Murray and C.F. Tedrow, Forensic Biology, Prentice Hall, New York, 1992.

J. Robertson, Forensic Examination of Fibres, 2nd Edition, Ellis Horwood, Chichester,

R. Saferstein, Forensic Science Handbook, Prentice Hall, New York, 1982.

B. Caddy, Forensic Examination of Glass & Paint: Analysis und Interpretation, Taylor

London, 1982.

Forensic Science Review, Central Police University Press, 1994.

1999.

and Francis, London & New York, 2001.

CHAPTER 4

Marks and Impressions

KEITH BARNETT

4.1 INTRODUCTION

Everything we do leaves a mark on the world. It could happen as we are


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walking, driving, working or sitting in the chair. While we carry out

these tasks our shoes, clothes, hands and even the tools we use can leave

unique tell-tale signs to the expert eye. A car will leave tyre tracks, the

shoes on our feet will leave footwear impressions and even the screw-

driver used to take the lid off the paint tin will leave its mark. The

simple principle that Locard proposed was every contact leaves a trace

and in the field of marks and impressions put two items together and

they are likely to leave a mark on one another.

Sherlock Holmes said in A Study in Scarlet that there is no branch of

detective science which is so important and so much neglected as the art

of tracing footsteps. The same is also true for the examination of tyre

tracks and the comparison of plastic bags of instrument and glove

marks. In all these cases there are features present that can be used to

form a unique connection between suspect and scene or stolen property.

The following chapter gives an insight into the methods used to recover

and present evidence at court in some of these areas.

This evidence can be divided into two distinct groups: damage based

evidence and non-damage based evidence. In the first group, which

includes evidence from footwear and instruments, an item has to

acquire damage in order to leave behind a unique impression. In the

second group, as with fingerprints, a combination of inherent features

provides the unique link. Any damage to the features of the fingerprint,

such as a scar, is not used in its classification as it may fade with time.

Just as it is true that no two fingerprints have been found to be the

same, even in identical twins, so in the examination of damage features


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Marks and Impressions 83

no two items, no matter how similar they are initially, are likely to

acquire the same random damage features during use.

In the first part of this chapter the evidence provided by damage and

wear will be addressed, specifically evidence that can be obtained from

footwear, instruments and mass-produced items. In the second part,

fingerprints and the evidence they provide will be discussed.

DAMAGE BASED EVIDENCE

4.2 FOOTWEAR IMPRESSIONS

4.2.1 Introduction

Every time a person takes a step, whatever the surface they are walking

on, they will leave behind a footwear impression. An impression could

be defined as the retention of the characteristics of an item by another

object. Hence over soft ground shoes impress themselves into it and

leave behind their characteristic impression. The impression left behind

is not always obvious and can be difficult to find without the aid of a

specialist technique. It is also vital that as many impressions as possible

are recovered from the scene of a crime as this will increase the chance

of finding an area corresponding to the area where the damage features

are located on the undersole of a shoe. It is possible that the undersole

has only one or two of these damage features present and they may all

need to be found to provide a significant link between a suspects shoe

and the scene of a crime.

4.2.2 Recovery of Impressions from Scene of Crime


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There are several mechanisms by which a shoe can leave an impression

b

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