Week 1 Part II

Question 1

What is trace evidence?

Answer 1

Trace evidence is evidence that occurs in such a small size that it can be transferred without notice.

Question 2

Lockard Exchange Prinicpal

Answer 2

Anytime there is a contact between two surfaces there will be a mutual exchange of matter across the contact boundary.

Question 3

What are controls?

Answer 3

Controls are known or reference samples that are used for comparison in the forensic investigation. The recovered samples are compared with the reference samples, as recovered samples alone are not entirely informative.

Question 4

What is a fibre?

Answer 4

A fibre is the smallest textile unit that is 100 times longer that it is wide. They are analysed to establish a connection between two or more people, or crime scene and person or object.

Question 5

Primary Transfer?

Answer 5

It the transfer of trace evidence from a source to an object or a person.

Question 6

Secondary Transfer?

Answer 6

Is the transfer of trace evidence from a source to another location/object or person and then to a another person on object.

Question 7

Persistence.

Answer 7

Is the measurement of the duration of time that the trace evidence remains on a surface. Initial loss of fibres is rapid (90-95%) in the first 24 hours and redistribution to a wider area of the garment can also occur.

Question 8

How many fibres are transferred?

Answer 8

This increase with the area of contact (but it is not directly proportional due to back transfer). It is dependent on the presence of contact. “The difference of the number of fibres transferred, is related to the difference in texture of the donor and the recipient fabrics”. Wool transfers more than fibres from smooth acrylics.

Question 9

What affects the rate of loss?

Answer 9

1) Continued wearing of the garment 2) Other garments been worn over the recipient garment 3) Contact of the recipient garment with other surfaces 4) Low original contact pressure.

Question 10

Comparison?

Answer 10

Is the usual way forward when analysing fibres and hair.

Question 11

Controlled fibres

Answer 11

Are collected from a known and uncontaminated source.

Question 12

Questioned fibres

Answer 12

Are recovered and compared with the control samples.

Question 13

Sampling of fibres

Answer 13

1) Must be highly efficient for removing transferred fibres 2) Should remove relatively few background fibres 3) A range of areas should be sampled to obtain distribution data 4) The fibres must be easily removed from the sampling device for further analysis 5) Rapid, cheap and easy to use.

Question 14

What maintains sample integrity?

Answer 14

Correct packing and procedures to minimise the risk of contamination.

Question 15

What is the correct packaging?

Answer 15

The correct packaging is to use paper bags and correct labelling.

Question 16

How do we reduce contamination?

Answer 16

1) Examiners need to wear protective clothing 2) Examine the victim and suspect in different areas and by different people 3) Do not transfer the suspect and victim in the same vehicle as secondary transfer can occur 4) Take control samples from the crime scene 5) Examine crime scene samples BEFORE the control samples.

Question 17

What do we use for sample collection?

Answer 17

Forensic Scientist use a variety of techniques such as vacuuming, shaking/brushing and tape lifts.

Question 18

Describe vacuuming

Answer 18

This is the process of vacuuming the crime scene and the recovered items to gather evidence. The disadvantages are that it collects a large number of background fibres and other loose debris as well as the target fibres.

Question 19

Describe shaking/brushing

Answer 19

This is the process of shaking garments onto a freshly prepared surface or brushing the crime scene or recovered garments. This process effectively recovers fibres, however it does not allow the fibre distribution to be measured.

Question 20

Describe tape lifts

Answer 20

This is the process of using adhesive tape lifts on the recovered garments. This allows rapid and efficient collection of samples. However it is time consuming.