Contamination of the scene and evidence

Define contamination

The longer the period between the offence and recovery, the greater the

likelihood that transferred material will be lost.

EXPLAIN LOCARD’S EXCHANGE PRINCIPLE

Every Contact Leaves a Trace

‘Any action of an individual and obviously, the violent actions of a crime, cannot occur without leaving a trace’

What does transfer occur between? primary transfer

• victim

• offender

• scene

Examples of secondary transfer?

• offenders address

• vehicles

• items handled

contamination vs transfer

Trransfer = movement of material from one source to another

contamination = transfer that compromises evidential value

List the factors affecting transfer of material

• pressure

• number of contacts

• time

• texture

example of pressure factor

An offender places a hand firmly on a window while

climbing through it, increasing the chance of leaving

fingerprints or palm marks.

example of number of contacts

A burglar repeatedly handles a drawer while searching

for valuables, increasing the transfer of DNA,

fingerprints and fibres.

example of time

A victim held in a prolonged struggle is more likely to

exchange fibres, hairs and DNA with the offender than

during a brief contact.

example of texture

A woollen jumper brushing against a rough wooden

fence is more likely to shed and retain fibres than a

smooth waterproof jacket.

What are the factors affecting retention of material

• texture

• washing

• activity

• time

FACTORS AFFECTING RETENTION OF MATERIAL example of factor

Glass fragments are more likely to remain embedded in a woollen jumper than on a smooth waterproof jacket.

FACTORS AFFECTING RETENTION OF MATERIAL example of washing?

Blood or trace fibres on clothing may be removed or significantly reduced during laundering.

FACTORS AFFECTING RETENTION OF MATERIAL example of activity?

An offender who runs, changes clothing or undertakes physical activity is more likely to lose transferred material.

FACTORS AFFECTING RETENTION OF MATERIAL example of time?

The longer the period between the offence and recovery, the greater the

likelihood that transferred material will be lost.

Give some examples of sources of contamination

• Personnel (to exhibit or DNA sample)

• Contaminated consumables or Packaging materials equipment

• Contaminated equipment

• Environmental factors

What barrier clothing/PPE needed for volume crime

•Face mask

• Gloves

• Second pair of gloves (when recovering items for DNA)

• Consideration further PPE

 or alternative barrier clothing should the scene require

What barrier clothing for major crime

•Face mask

•Mob cap/hairnet

•First pair of gloves

•Scene suit (hood)

•Overshoes

•2^nd pair of gloves