Lecture 7 - Trace and Contact evidence

Question 1

Forensic evidence =

Answer 1

evidence with a scientific basis which is used in the court of law

Question 2

3 categories of forensic evidence =

Answer 2

Forensic evidence can be broken up into 3 categories : biological, physical and impression evidence

Question 3

Fingerprints are made up of

Answer 3

sweat and within this sweat is DNA

Question 4

Lockard’s exchange principle

Answer 4

With contact between two items there will be an exchange.

Every contact leaves a trace
This is the founding principle of forensic science

Question 5

Important distinction should be drawn between whether the purpose of the examination is to

Answer 5

provide intelligence or to evaluate the strength of evidence for use in court AND whether quantitative or qualitative analysis is being done on the forensic evidence

Question 6

Searching for forensic evidence summary …

Answer 6

first visual screening
then use the visual screening crime lite
a new technology evolving is crime-lite auto which is the future

Question 7

Before using anything to search for evidence …

Answer 7

use your eyes

can use sunlight, white light/torch or oblique light

Question 8

Visual screening - Crime lite

Answer 8

Crime lites use different wave lengths to identify and visualise stains, hairs, fibres, gunshot residue etc

Hand-held, high intensity light source
Filters alter wavelength allowing forensic evidence to be targeted.
Blood, semen, saliva, bone, teeth, hair, fibres, shoeprints, fingerprints, gunshot residue and accelerants.

Question 9

Technology evolves - crime lite auto

Answer 9

In a camera, now not two separate devices i.e. video, camera and crime lite all in one
This is the type of technology that is coming to NZ

Question 10

Biological evidence =

Answer 10

Body fluids or cells containing DNA which can be used for identification purposes.

So when you find something that is a suspect stain you need to do sampling with it to test it first so the next thing you want to do is chemical testing

Question 11

Chemical testing for biological evidence - different tests based on what bodily fluid is being investigated…. Blood =

Answer 11

Combur, KM, Luminol

Main ones are for blood because when a crime scene is messy there is usually a lot of blood to sample from

Question 12

Chemical testing for biological evidence - different tests based on what bodily fluid is being investigated…. saliva =

Answer 12

Phadebas

Question 13

Chemical testing for biological evidence - different tests based on what bodily fluid is being investigated…. semen =

Answer 13

ACP

Question 14

Chemical testing for blood - COMBUR

Answer 14

Catalytic reaction of haemoglobin on a peroxide substrate

Colour change from yellow to green

Sensitive but not specific
Tiny speck of blood can cause a reaction but it also means that a lot of other things can cause a reaction, more likely to give you a false positive
This test is carried by senior crime officers, more portable and easy to use, looks like pH sticks
Presumptive test for blood
Can react with other things such as some vegetable materials which contain the enzyme peroxidase which may give positive results

Question 15

Chemical testing for blood - KASTLE MEYER

Answer 15

Phenolphthalein is used to detect possible presence of haemoglobin

Colour change to pink

Less sensitive but more specific
May not react with tiny amount of blood but less likely to give you a false positive which the COMBUR is likely to give you

Question 16

Chemical testing for blood in general

Answer 16

At the scene of a crime, presumptive tests may be used to detect the presence of blood that might otherwise be overlooked, either because it occurs in minute amounts or because it merges well with its background.
The presumptive tests used for blood are based on the ability of the haemoglobin present in red blood cells to catalyse the oxidation of certain reagents.

Both testsreact to the same part of the blood, but varies in their reactions

Question 17

Luminol

Answer 17

Luminol reacts with iron found in haemoglobin causing luminescent.

It is non-specific meaning other substances can cause a reaction including bleach, copper and horseradish.

Dead end treatment, meaning that it is the last thing done at the crime scene because once you spray it it causes damage to the sample and starts to degrade the sample

Needs to be dark in order to see the fluorescence

The image we saw in class of the footprints on the stairs treated with luminol you can say that someone with blood on their shoes was walking down the stairs, there is more blood on the left shoe than the right shoe, there is enough detail in the pattern of the shoe to give us a class match so you can say what type of shoe it is that left that footprint behind 
Theses kinds of photos are quite powerful to use in court

Question 18

Chemical testing for saliva - PHADEBAS

Answer 18

Saliva is rich in the enzyme alpha- amylase (α-amylase)

The Phadebas Test reacts to α- amylase by releasing a blue dye

Presumptive test indicating saliva may be present (amylase is found in other body fluids at lower levels)
It is a sheet of paper that is placed on top of the item and then you get it wet and then have a look at it and then the area that has saliva present changes to blue in colour

Question 19

Chemical testing for semen - ACP (acid phosphatase)

Answer 19

Acid Phosphatase (ACP) is found in unusually high concentrations in semen
ACP is an enzyme that is secreted by the prostate gland, it is found in high concentrations in the seminal fluid compared with other body fluids 

A suspect stain is sampled by swab or damp blotting paper and a solution (sodium alphanapthylphosphate and fast blue B) is applied producing a purple-blue colouration if positive.
Visually search with crime lite first to look for areas of fluorescent until this is made redundant
Blotting paper used and make it wet and then what was ever on that surface is transferred on to the blotting paper and then you take it off the surface and turn it over and treat it with ACP spray and then any areas where there is potentially seminal fluid turn purple and then you match it back to the surface where you take further tests from

In cases of sexual abuse and rape, the presence of semen at the crime scene provides highly important forensic evidence. As might be expected, semen can be recovered from the body of the victim in many cases. In addition, semen may also be collected from, for example, used condoms, bedding, clothes, furniture and carpets.

Question 20

Blood, saliva and semen are all examples of biological materials and as such may

Answer 20

be used to link an individual with a specific crime scene using the technique of DNA profiling 


Question 21

Collecting biological evidence

Answer 21

Risk Assessment
Since it is a biological hazard you need to do risk assessment
For example consider hepatitis, AIDS or whether it is a COVID situation

PPE – gloves and mask (minimum)
For something more serious you are going to be fully kitted out … Eye protection, gloves, masks, disposable suit, booties, hairnet, hood

Records – photos and notes
Record how it was before you make any changes

Use sterilised/sterile equipment
To prevent yours or others DNA coming into the scene

Question 22

Collecting biological evidence - blood

Answer 22

One wet swab using sterile water

Have swab - take it out whilst wearing gloves and a mask - put three drops of water on the end of it without touching the end (prevent contamination) - roll it through the blood stain - then back into the tube with sterilised tweezers - make a hole in it to let the air in to prevent it degrading - then in an envelope where it is sealed, signed and labelled
DNA is in the white blood cells not the red blood cells therefore you can’t see them so you roll the swab around the blood stain

Question 23

Collecting biological evidence - saliva

Answer 23

Two swabs – one wet then one dry

Put it around the top of the bottle/can where someone has drunk from or handled it
Two swabs are counted as one sample and they go into one envelope

Question 24

Collecting biological evidence - trace/touch (invisible, you can’t actually see these)

Answer 24

Two swabs – one wet then one dry

Can get a DNA profile from the swab of a touch/trace
Two swabs go into one envelope and are classified as one sample

Question 25

Collecting biological evidence -cigarette butt

Answer 25

Entire item into envelope

Sterile and/or disposable tweezers used to put it into the envelope and then you seal the envelope and label it

Question 26

Collecting biological evidence - clothing

Answer 26

Entire item into paper bag

Usually do with a partner to put in bag, your partner holds the bag open for you, you do not but your arm inside to try make space for the clothing because you risk contaminating the bag with fibres, hair, skin cells, DNA etc
Use the weight of the item to put it into the rubbish bag and then you fold it over twice, tape it and label it
Want the entire item because it can provide biological evidence - not only biological evidence but it can also hold fibres, glass, paint

Question 27

Physical evidence =

Answer 27

Physical, microscopic and chemical evidence.
Known as the catch all group
Some of it you can physically pick up and some of it is invisible

Tangible items which can be collected from a crime scene.
Some is invisible so referred to as trace physical evidence

Question 28

examples of physical evidence

Answer 28

It it a broad grouping, so if it doesn’t fit into impression or biological then it is probably a physical item of evidence that you are talking about

Glass
Paint
Fibres
Soil and Pollen
 Hydrocarbons 
Gunshot residue 
Explosives

Question 29

Physical fit

Answer 29

Pieces left at a scene can be linked back to the source
If break pattern is so unique, then it is very strong evidence to match up for an ESR scientist that is testifying i.e. can say this fragment of glass belongs to this car
Such as in hit and runs
ESR scientists would testify in court about pieces being consistent with fitting into the source that is linked to the crime that has occurred

Physically fitting the pieces back together
Can also use the help of witness and CCTV to piece it back together

like a jigsaw puzzle

Question 30

Glass broken/smashed can be linked to what kind of events

Answer 30

ram raid
assault with bottle
hit and run

Question 31

Linking glass fragments back to the source

Answer 31

Refractive index 
Density
 Thickness 
Colour
Physical fit

Question 32

What happens when you smash a window?

Answer 32

Some goes into the car and some of it goes back towards the person smashing the window
Can look for glass landing on the offender

Question 33

Collection considerations for smashed glass

Answer 33

Collection Considerations: Backscatter ~ 30% Persistence ~ 24hrs
Backscatter = the amount of glass coming back at the person, depends on the lamination too, will land on their clothing, hair and anything else they have on them
30% of the glass that is smashing is going to come back onto the person that is smashing the glass
Stays onto them for about 24hours, on the run from police means that less likely to stay on suspect
The more texture on the material, the longer it will hold onto that glass
Lamination also determines how much glass will fall back onto them
Seize items of clothing when offender caught and shake them on pieces of paper

Question 34

Packaging considerations for glass

Answer 34

Packaging Considerations: Sharp Can pierce paper

Put it into plastic or into something that can be sealed

Question 35

what is the glass compared to?

Answer 35

Control samples

Control (or reference) sample from broken window
Control sample not taken from ground because it could come from anywhere

Refractive Index varies slightly across a window

10 samples taken from around the window
10 control samples from different parts due to the differing refractive indices

Not from the ground
Need to be able to say that it is from that window

Question 36

Paint can be linked to what kind of events?

Answer 36

hit and run
ram raid
assault with painted object - - If someone is assaulted with a painted crowbar or a painted baseball bat then often bits of the paint will be embedded in their skull or wherever else they have been struck
burglary

Question 37

Linking transfer back to source ….

Answer 37

Layers

Colours

Microscopy
Put under a comparison microscope to compare samples of the paint to each other

Physical fit
If paint chip is big enough

Question 38

What is the paint being compared to …

Answer 38

Control samples in the instance of a car

From damaged panel

Away from the area of damage

Multiple samples
Multiple samples because the paint may change across that panel

All layers down to the base (i.e. multiple samples in this regard too)

Question 39

Collection considerations of paint

Answer 39

easily lost

Question 40

Impression evidence =

Answer 40

Contact between two surfaces leaving a mark which can be used for identification purposes.

Impression evidence is contact between two surfaces where a harder surface is going to leave a mark on the softer surface

Question 41

Impression evidence example

Answer 41

tool mark

Question 42

Tool marks

Answer 42

Tool marks, often a screwdriver or a crowbar, to force something open that leaves a mark behind and the mark left behind can be matched back to that tool that was used to make that mark

Created when a tool is used to force open a window or door.
A mark will be left on the softer surface.

Question 43

What is used to make cast of a tool mark

Answer 43

Use Mikrosil in the police (there are other products out there), 2 part casting material often used to collect impressions of tool marks or fingerprints, mix the blue and the brown together where the blue is the hardener and put it on the tool mark and let it set and then lift it off, cast which has been collected can then try to be matched to any suspect calls gotten

Question 44

Linking toolmark to tool

Answer 44

use class and individualising characteristics … Example in the case of a shoe print - class characteristics means that it is brand new type of situation and you can say what size and type/make of shoe it is, if you have wear tear and damage then you can say that THAT shoe made that mark rather than only being about to say the class of shoe

Question 45

Class characteristics

Answer 45

No damage
Original condition
Link tool mark to type and size of tool used

= characteristics that enable an object to be placed unto a particular category for example identifying a trainer as belonging to a certain brand

Question 46

Individualising characteristics

Answer 46

Wear and damage
Microscopy used
Link tool mark to specific tool used

= Characteristics that are unique to a particular object (e.g. a particular tool, tyre, or shoe) and as such are potentially useful in the identification of scene impressions

Question 47

class vs individualising characteristics

Answer 47

Class characteristics Means that typically this tool is new, there is no damage to it yet and it is in its original condition whereas individualising characteristics means that there is now wear and tear and damage to the item and microscopy can be used to look at the damage on the item 
If we only have class characteristics then you can say this type of tool and this size of tool has been used, and if we have individualising characteristics then we can say this type, this size AND THIS tool was used at the crime scene and then the next step would be trying to put this tool into someones hand