CSI Dundee Flashcards
Locard’s exchange principle
“every contact leaves a trace”
Describe ‘jigsaw’ evidence
Physical match between part of substance on victim and other part on attacker.
what are the main examples of trace evidence found on clothing?
hairs, fibres, glass, paint, GS residues, vegetation, pollens
how is paint analysed as trace evidence?
flakes of paint on clothing can be microscopically examined to determine the layer structure and thickness for the paint and matched with another sample e.g. from a suspected car in a hit and run
vomit can stain clothing and be analysed. a pink-tinged vomit might indicate the victim ingested what?
amitriptyline can tinge vomit a pink colour and can be used in overdose
what can the pattern of a blood stain tell you?
if the victim was standing or lying down when injured
e.g. a person standing up that stabs themselves would have blood flowing down following gravity and might have moved clothing out the way - if blood stain is horizontal then they were lying down
if clothing is in the way of the injury and also stained, this might suggest an attack over suicide.
Give examples of low velocity blood patterns.
dripping, cast-off from weapon, splashing or arterial spurting
Give an example of a medium-velocity blood pattern.
baseball bat injury
Give examples of high velocity blood patterns.
gunshots or machinery related injuries
The higher the velocity of the injury, the larger the droplets of blood - true or false
FALSE
the higher the velocity, the smaller the droplets
e.g. HV gunshot -> fine mist
The smaller the droplets, the further they can travel in air - true or false
FALSE
smaller droplets travel shorter distance in air
e.g. fine mist from gunshot would only hit those in close proximity to victim
What test can be done at a crime scene to confirm presence of blood in a stain?
Leuco Malachite Green
What are the pros of Leuco Malachite Green?
it is a minimally destructive chemical test
It can be used at the scene
When assessing the point of convergence, shorter and fatter blood splatters hit the surface at a smaller angle - true or false?
true
shorter + fatter blood splatters hit surface at smaller angle
How do you assess convergence in 2D?
draw lines through splatter to find direction of infliction
Describe a typical arterial spurt pattern and in which situation it would be seen.
up and down cycle = arterial spurt common in (suicidal) neck incisions
Blood transfer/smearing noticed on wall in a brush stroke pattern - what does this suggest?
a bleeding head wound or blood stained hair wiped along the wall.
the height of the smear on the wall tells you if person was standing or crawling
Mud or soil can be used as evidence, where will you look for it?
sources: clothing, footwear and tyres especially
What is noted about evidential mud/soil?
colour when dry
particle size & density
mineral composition
biological composition (plants, pollens, microbiology)
a mud/grass stain on the seat of jeans suggests what?
wearer was dragged by legs
plant pollens are fragile particles - true or false
FALSE
plant pollens are highly resistant particles
what can paint pollens be used to confirm?
they can confirm a suspect was in a particular area and also tell you at what time of year and sometimes what time of day - due to seasonal and diurnal variation
Where can you take pollen samples from?
soil cars (tyres, wheel arches, upholstery) hair clothes, shoes under fingernails nasal cavities gut firearms other substances (drug packages, explosives)
what is probably the most common type of trace evidence?
fibres
a forensic scientist is usually able to individualise fibres provided as evidence - true or false
FALSE
due to mass production, it is not usually possible to individualise fibres
Examples of animal fibres.
animal fibres = proteins
silk = fibroin
wool and hair = keratin
Examples of vegetable fibres.
veg fibres = cellulose - seed, stem and leaf fibres
Example of a mineral fibre.
asbestos
More common fibres have less evidential value - true or false
true
more common fibres like denim have less evidential value
Describe the possible mechanisms of transfer of fibres.
- Loose fibres may shed.
- Embedded fibres may be pulled out or shed.
- Fibres can break under stress > shed
what techniques can be used to examine fibres?
microscopy - comparison, polarised light, light, UV light
Infra-red spectroscopy
chromatography
Fibres examined under light and comparison microscopy look identical but once under polarised light, some differences are noted - do they still count as a match?
no, once a difference is recognised they are no longer considered the same
DNA can be detected in saliva. What are some potential sources of saliva?
apart from obvious spit, bite marks, stamps/envelopes, cigarettes, drinking glass
What samples associated with a person’s scalp might offer DNA samples?
dandruff and hair follicles
hats
Semen is the main source of DNA related to males in sexual incidents, but how might you identify a female victim if you have the male suspect?
vaginal/endometrial cells from victim can rub off onto penis and persist for around 24hrs
these cells might be found on the suspect’s underwear
a used condom will have male DNA on inside but vaginal/anal cells on outside (gives you victim and attacker)
normal pH of semen
pH 7.2-8.0
main components of semen
spermatozoa acid phosphatase (AP) Prostatic specific antigen P30 (PSA) choline spermine
how long can motile sperm last in vaginal canal?
usually only live 4-6hrs in acidic vaginal canal
not normally found >16hrs after intercourse
how long do non-motile sperm last in vaginal canal?
in upper vagina, up to 3d after sex, sometimes >6d in cervix
Apart from drainage, how else might spermatozoa be lost as evidence following sexual intercourse?
(drainage)
dilution: vaginal secretions, saliva
degradation: seminal enzymes, loss of tails
defaecation
washing/showering after sex
how long can sperm last in mouth - what does this mean for swabs?
<6-12hrs in mouth
swab <2d
how long can sperm last in upper vagina?
<6-12hrs if motile
<3-6d if non-motile
how long can acid phosphatase last in upper vagina?
AP <48hrs
how long can sperm last in the endocervical canal?
7-10 days
how long after intercourse can you swab vagina for spermatozoa?
upper vagina swab <7d
how long can sperm last in anus and rectum - what does this mean for swabs?
anus: <2d
rectum: <3d
swab rectum <3d
What lab samples do you take from a female victim of sexual assault?
clothing head hair swabs of mouth/saliva fingernail scrapping, clippings ± swabs skin swabs pubic hair vaginal swabs ano-rectal swabs blood
what swabs do you take of bite?
moist and dry swab
What is the swabbing technique required for vaginal swabs (timescale + no.)?
take them within 7 days vulva: double swab technique lower 1/3 (3-5cm): 2x dry upper 2/3 (speculum): 2x dry endocervical canal: 2x dry
What is the swabbing technique for ano-rectal swabs?
take within 3 days
perianal skin-3cm radius from anus: double swab technique
anal canal (rotate at 2-3cm): 2x dry
rectum (proctoscope, >4cm): 2x dry
When and how do you collect a mouth swab?
collect if oral penetration occurred within 2 days
2x dry swabs rubbed over + under tongue, over all sides of teeth, gums and inside cheeks.
mouth rinse with sterile water into polypot (police kit)
when do you collect a vaginal swab?
digital penetration <12hrs
vaginal intercourse <7d
anal intercourse <3d
When do you collect anal swabs?
digital penetration <12hrs
anal intercourse <3d
what is the swabbing technique for penises?
double swab technique for shaft, foreskin/coronal sulcus and glans
what laboratory technique is diagnostic for spermatozoa
microscopy
Acid phosphatase if detected, confirms semen was present - true or false
FALSE
AP is not specific for semen -> false positives
AP is found in low concentrations in vaginal secretions and other bodily fluids
PSA if detected, confirms semen was present - true or false
PSA is secreted into seminal fluid and is an accepted marker for semen in criminal cases
If a male suspect is believed to have had a vasectomy, how can you test trace evidence for sexual intercourse?
PSA is a good marker for semen in persons lacking DNA in sperm e.g. azoospermia or in those who have had a vasectomy
how long is AP detectable after ejaculation and what colour test is used?
detectable up to 48hrs after
colour test: purple in <30s = positive
a flame-shaped hair root which is attached to the follicle is seen in which phase of hair growth?
anagen phase
an elongated root shape and slow growth is seen in which phase of hair growth?
catagen phase lasts 1-3 weeks and is slow growth with elongated root shape
a club-shaped root is seen in which hair growth phase?
telogen phase lasts 2-6 months and has a club-shaped root
Hair cuticles have a resemblance to which structure and what do they indicate?
overlapping scales of keratin resembling roof tiles
the cuticle pattern indicates species
which part of hair contains pigment granules
cortex of hair contains pigment granules
the colour, shape and distribution of these granules is important
which part of hair structure is arranged in parallel spindle cells in regular parallel way?
cortex
The medullary canal of a hair strand is always continuous - true or false
false
can be continuous, interrupted, fragmented or absent
what can the medulla of hair tell you about the person?
if medullary canal is absent or interrupted it can indicate race.
it will be a continuous canal in monogloid persons
what can the morphology of the scales, cortex and medulla of hair tell you?
the body area, racial origin, sex (bleching, dyeing) and age of a person
if hair is forcibly removed what will also be seen microscopically?
sheath cells seen if force used
comparison of hair strands can individualise persons - true or false
false comparison of strands (without DNA) cannot individualise
what kind of samples can be taken during arrest?
non-intimate samples - fingerprints, palm prints, other impressions, photographs
What kind of samples can be taken during arrest if inspector gives permission?
body hair (not pubic)
finger/toe-nail clippings or other nail material
blood or other body tissues or fluid gained by swabbing or rubbing
saliva that can be swabbed from the inside of the mouth
blood samples are a routine sample taken on arrest - true or false
false
blood samples can be taken with a warrant
upon detention or arrest, police have the power to carry out DNA test - true or false
true
= cells scrapped/swabbed from inner cheek lining
What does the National DNA database hold?
DNA profiles from those arrested or charged with, or convicted of a recordable offence
also DNA profiles obtained from crime scenes
What are the 6 benefits of the National DNA database?
- Early identification of linked cases (serial crimes)
- Early arrest of offenders
- Valuable intelligence
- Early exoneration of innocent suspected
- Easier identification of bodies
- Deterrence
Police takes prints and impressions of suspect - when will these be destroyed?
destroyed if don’t get convicted of crime
if convicted, prints, impressions & DNA records can be held for up to 2 years (or 3 if a particular violent or sexual offence) if the accused accepts an alternative to prosecution e.g. a fine or work order
How long can DNA and prints from a violent ± sexual offence be kept for by the police?
for up to 3 years even if accused is acquitted by court or case is dropped.
police can also apply for an extension of up to 2 years at a time
urine is classed as an intimate sample - true or false
true
so is blood and dental impressions
consent is always sought for an intimate sample - true or false
TRUE
However, an intimate sample can be taken from a person in police detention on authority of the Inspector if there are reasonable grounds for suspecting the involvement of the person in a recordable offence and that this sample will confirm or disprove this
a doctor can take an intimate sample without consent - true or false
TRUE … in theory, however unlikely in real life
Inspector can order this but not many Drs will risk their license
what swabbing technique is performed for fingernail scrapping?
2 swab technique (1 wet 1 dry)
what is the double swab technique?
- moistened swab rolled over skin - rehydrates and loosens foreign cells
- dry swab rolled over same area - picks up foreign cells
vaginal swabs are taken from endocervical canal > upper vagina > lower vagina > vulva - true or false
FALSE
swabs must be taken from outside in to avoid contamination of samples
why is double swab technique used?
this technique results in higher recovery of cells/DNA and is used on skin (bit), vulva and penis
When labelling specimens, what needs to be documented?
name of subject type of specimen date & time collected name of collector (FME or nurse) name of witness (nurse) name of police officer
The supernatent acquired from extraction of material on vaginal swab is tested for what?
stained with H&E for sperm identification
supernatant tested for Acid phosphatase, amylase, ABO, choline
cellular fraction remaining is combined with expressed swab and used for DNA profiling
what is the chain of custody?
the legal term that refers to the ability to guarantee the identity and integrity of the specimen from collection through to reporting of the test results.
process used to maintain and document the chronological Hx of the specimen
what happens if the chain of custody is prolonged or messy?
the defence lawyers will say that the evidence is unreliable
stress marks of glass fracture are aka. ?
Wallner lines - seen along edges
what do stress marks on fractured glass show?
show direction from which pane was broken
Radial cracks have ridges at ? angles to the ? face
radial cracks have ridges at right angles to the rear face (all r)
Concentric cracks look like ?
spider’s web
concentric cracks have ridges at ? angles to the ? face
concentric cracks have ridges at right angles to the front face
Why does tempered glass tend to shatter?
it is less flexible due to heating and cooling process it has been through
What modification has been added to car windscreen glass?
windscreens are now laminated (plastic sheet in middle of glass) to prevent ejection of passenger in RTA
a bullet passes through glass, how can you tell the direction it was traveling in?
bigger proportion of glass shattered on side the bullet was travelling to
i.e. side of glass the bullet exited from has larger amount of broken glass
a crowbar leaves a 3D mark in the softer windowpane - what is this type of mark called?
3D marks in soft material = impression
a crowbar leaves a 2D scratch on the windowpane surface - what is this type of mark called?
2D linear scratching of surface = striation
tool marks can tell you the type of tool and shape as well as any individual imperfections - true or false
true class characteristics tell you general groupings such as tool type, size and shape individual characteristics tell you any unique features of a weapon (transient or permanent)
give an example of a transient individual characteristic?
e.g. a stone trapped in shoe grip will imprint but stone can fall out = transient
footwear can make marks in mud, sand and snow - what kind of marks are these?
impressions in soft material (3D) = mud, sand, snow
footwear can make marks in blood, dirt, or dust - what kind of marks are these?
prints on hard surface (2D) = blood, dirt, dust
A person who was shot with gun pressed/very close to chest - what can the trace evidence tell you?
muzzle imprint - e.g. 12G shot gun + which barrel (right/left)
soot - elemental components
