trace evidence analysis

Question 1

trace evidence

Answer 1

microscopic quantities of material that are of probative value in a forensic investigation.

Question 2

types of trace evidence

Answer 2

biological- (human)
physical- biological (non human)
particles, substances, marks/impressions
natural vs manufactured materials

Question 3

forensic value

Answer 3

establish spatial and temporal links between persons and scenes of interest.

Question 4

forensic process- trace evidence

Answer 4

transfer-> persistence-> collection-> analysis-> interpretation-> presentation

Question 5

evidence dynamics

Answer 5

any influence that adds, changes, relocates, obscures, contaminates, or obliterates physical trace evidence , regardless of intent. transfer- during crime. persistence- after crime.

Question 6

modes of transfer

Answer 6

one way- evidence is passed from one thing to another.
two way- evidence is dispersed onto multiple objects. reduces the chance that the trace evidence has been picked up innocently.

Question 7

modes of transfer

Answer 7

direct- person touches the evidence
secondary transfer- person not at the crime scene but evidence has been transferred to them

Question 8

how useful is trace evidence following transfer- 1. variation in transfer

Answer 8

amount and distribution of transferred evidence varies.

Question 9

1. variation in transfer- clothing

Answer 9

varies in composition and texture.
influences fibre shedding (creation of evidence). influences adhesion of other traces. eg nylon vs wool.

Question 10

1. variation in transfer- weather

Answer 10

local conditions affect transfer of environmental trace evidence (source). influences deposition of other types of evidence at the scene.

Question 11

1. variation in transfer- trace characteristics

Answer 11

particle size/ shape. glass- fragments (mm) or particles (um). pollen- different sizes and surface textures.

Question 12

how useful is trace evidence following transfer 2. frequency

Answer 12

is the trace evidence easily transferred? how commonly is the trade naturally encountered. transfer is not a discrete event- pre and post crime transfers.

Question 13

3 trace persistence- wear

Answer 13

loss of evidence over time. fibre persistence on different clothing items. similar trends with most traces (GSR, paint, glass). other types of trace evidence is more complex.

Question 13

2 frequency- pollen

Answer 13

abundant in the environment. transport mechanisms- direct/ indirect transfer. present in most peoples hair, shoes, clothing. individual pollen profile.

Question 13

2 frequency- glass

Answer 13

population studies- frequency in general populations. rarity amongst general public= forensic significance.

Question 13

how useful is trace evidence following transfer 3. trace persistence

Answer 13

temporal dynamics of transferred evidence. how long is the evidence preserved for after crime events? impacted by source/ recipient, environment, evidence characteristics, initial transfer.
absence of evidence is not evidence of absence.

Question 14

3 trace persistence- offender activity

Answer 14

post crime activity may also contribute to loss of trace evidence- offender, bystander, police/CSI. eg washing burning, cleaning, vacuuming. packaging exhibits- loss or redistribution of evidence.

Question 15

trace analysis

Answer 15

identified via class characteristics (colour, shape, RI) aim to establish points of similarity between samples- how rare. if properties differ= not from the same source. absolute identification often not possible- exclusion.

Question 16

classifying evidence

Answer 16

morphology, optical, physical, chemical properties. general physical characteristics- mpt, bpt, RI, absorption and emission spectra (IR, vis, UV), density, molecular mass, colour, species characteristics.

Question 17

classifying evidence techniques

Answer 17

non destructive- priority. physical eg microscopy.
destructive- further information. chemical eg chromatography, mass spectrometry.
depends on the amount/ value of evidence, type of crime, aims of enquiry, resources.

Question 18

microscopy

Answer 18

the microscope is the most fundamentally important tool to trace evidence.
it analyses many types of evidence- 3D, microscope slide. surface analysis & look through objects. many times of microscopy.

Question 19

stereo microscope

Answer 19

preliminary examination (30x magnification). segregate evidence from other material- substance type, size, form, colour, texture, appearance.
guides more in depth analysis. isolation of individual particles.

Question 20

compound microscope

Answer 20

high power examinations (100-1000x mg) transmitted light= sample preparation. light from the base, through condenser & specimen. light passes through objective lens & ocular lens

Question 21

scanning electron microscope

Answer 21

higher magnification (10x to 500,000x mg) often needed. samples gold coated. scans surface with focused high energy electron beam. secondary electrons detected= creates image. combine with chemical analysis (XRD, EDX, EDS).

Question 22

summary

Answer 22

trace evidence is valuable when recognised, detected and collected. important to use non destructive analytical techniques first. understanding trace evidence dynamics assists with crime reconstruction. anything can be trace evidence= diverse analysis approach. importance to exclude rather than match.