Trace evidence and tool marks

trace evidence

- physical evidence found in small amounts at a crime scene

e.g. glass, hairs, fibres, paint, pollen, metal particles, drug residue, firearms

value of trace evidence

• Dependent on how common or rare a material or combination of materials is in the environment, the location or circumstance

• Rare materials or combinations of materials have a higher evidential value than those commonly found

number of fibres transferred depends on

• Nature of donor garment

• Texture of recipient garment

• Length of contact

• Pressure on contact

• Number of contacts

number of fibres found on a garment depends on

• Whether garment has been washed

• Whether it was worn after offense

• Length of time it was worn

• Texture of the garment

After 4 hrs 20% fibres remain

After 8 hrs 10% remain

After 30hrs 3% remain

As time of wear increases fibre percentage decreases

 both visible fibres and fibres that cannot be seen will be found at scene

visible

fibres you cannot see

Use tape on surface, put onto acetate and place into tamper evident bag

fibre lifts

Use low tack adhesive tape

Press tape onto suspect surface

Place onto a cobex/acetate sheet

Use cellotape to secure edges of tape to stop any loose fibres falling out

Endorse sheet with details in indelible ink (5 pieces of info)

• Exhibit no

• What it is and where from

• Date/time

• Address

• CSI name

 

car seat fibre tape lift locations

1. Door panel

2. Seat base

3. Seat back

4. Head rest

5. Seat belt

All become one exhibit- label with where in car it came from HT/01

Try to separate sections into exhibits

glass

- flat

-Float

-Toughened

-Tempered

-Safety/laminated

-obscured

-patterned

-wired

-mirrors

-containers

glass at crime scene

• Small samples- into universal tube then bag

• Larger samples - box - seal edges

• Window glass - must be from frame - 6 pieces label inside + out

• Double glazes units - 6 from out and 6 from inside pane

• Samples from each window smashed - separately

• Do not recover window glass from floor - if have no choice document where its recovered from

backward fragmentation

If you smash a window - glass will smash backwards coming towards you

Helps think about where glass may be on person

e.g. smashed glass on top of shoe - suspect

Smashed under sole- walked through it

primary - forward

secondary - backward

retention properties of glass

• Course knitted jumper           good

• Fine knitted jumper/tweed                                        

• Denim jacket

• Tshirt                                            poor

 

evidential value of glass fragments on suspect/victim

High           hair combings

                    outer clothing (upper)

                   outer clothing (lower)

                   pockets and turnups

Low           shoe soles

examination of glass in lab

Glass Refractive Index Measurement (GRIM)

Chemical Analysis

Surface Characteristics

Physical Fit (larger fragment)

paint

 

Can associate a person or vehicle with a crime scene

• Traffic incidents - paint transferred from and to vehicle

• Burglaries - paint transfer to tools

Vehicles - paint can determine make, model, colour, year

paint transferred by

• Forceful contact

• Contact with disturbed paint

composition of paint

Composed of:

• Binder

• Pigment

• Additives

Most paint applied in layers

two way transfer

Can provide conclusive evidence

Tool came into contact with a surface

Vehicle was involved in RTA

Clothing came into contact with a surface

BEST PRACTICE

Remove complete article bearing mark or paint sample when possible

sampling paint at scene

Always photograph first

• Use sterile new scalpel blade

• Sample (scrape) down to bare wood/metal

• Approx 2cm square if possible

• Seal in paper wrap/ universal tube and plastic bag

• Include scalpel blade - secured blade - into original packaging

• Label

• Take control sample from undamaged area of same item

evidential value of paint

more paint layers = more conclusive

tool marks

Any impression, scratch, gouge, cut or abrasion made when tool is brought into contact with another object

types of tool marks

1. Compression

Most common

Negative impression of tool

Caused by pressure, blow or gouge

1. Friction

Sliding/scrapping

Leaves striation marks

Created by forced application of tool to surface

1. Cutting edge

Least common at scene

Combination of two impression types

From tool mark both class and individual characteristics of tool can be identified

levering tools

Jemmys

Screwdrivers

Metal bars

Crowbar

cutting/drilling tools

Scissors

Pliers

Saws

Bolt cutters

types of levered marks

Opposing marks - door/window edge, frame - should match up

Fulcrum/leverage - point about which the tool pivots, not always present or sometimes merged with tip marks

recovery

Recovery whole item bearing mark if possible

Photograph with and without scale and label

Recover end marks and fulcrum mark

Cast early in exam - probil

Package in sealed labelled box or rigid container

Two/three casts = one exhibit but clearly identify which is which e.g. door edge, door frame and fulcrum marks from same tool

drilled holes

Recover whole if possible

Photo with and without scales

Cast early in examination

Package casts in a rigid container

Collect swarf/turnings/shavings

• Package in a universal plastic tube or box

packaging levering tools

Rigid container

Weapons tube (don’t over tighten) - tape and sign

Make packaging fit tool - don’t introduce contamination

Shouldn’t move in packaging - friction destroys evidence

what to do with cutting tools

Item shouldn’t move in packaging

Don’t close jaws

Seal in close fitting box - do not introduce contamination

dealing with fencing wire, telephone wire, chain fences

• Cut 15cm back along wire

• Label and protect with paper

• Label 'own cut end' and 'crime cut end'

• Seal in box and attach CJA label