Crime Scene Management: Chapter 5.2-5.7, 5.10-5.12
5.2 nature of friction ridge skin
unique ridges on fingers, palms and feet
raised ridges and associated furrows, contain creases and many sweat pores
without friction ridges ability to grip items is reduced and action of holding something is more difficult
friction ridges form before birth in embryo development
stratum basale (generating layer) of epidermis forms prior to birth - doesnt change
5.3 structure of friction ridge skin
thick skin includes friction skin has two principal layers
epidermis is layered, flat epithelial tissue five layers thick
dermis is thicker than epidermis consisting of two layers, papillary and deeper reticular layer
dermis sustains epidermis
papillary layer - connective tissue with fine elastic fibres
surface area of layer is supplemented by dermal papillae
formations increase SA to facilitate exchange of oxygen, nutrients and waste products between dermis and epidermis
boundary between dermis and epidermis is point of potential weakness
two tissues can be separated from each other
evident in cases of decomposition and long immersion in water where outer layer of friction ridge skin can slough off
5.4 friction ridge growth
fingerprints are persistent and unique
1929 Harold Cummins - how growth of epidermal friction ridges is dependent on variations in histology of different regions and differential growth incident to the production of irregular reliefs of the volar surfaces
he says: various configurations are not determined by self-limited mechanism within skin
skin possesses capacity to form ridges, but alignment of these ridges are responsive to stresses in growth as are the alignments of sand to sweeping by wind or wave
other words = friction ridge patterns arent just result of genetic factors byt also random physical stresses and tensions
5.5 principles of friction ridge identification
friction ridges are not uniform in configuration, nor do they flow in straight lines
ridges have fractures and interruptions within the structure known as Galton details, ridge characteristics or minutiae
Galton studied heritability and racial differences in fingerprints - unique
technique for identifying common patterns and devised a classification system
these characteristics when visible enable determination of individualization of a latent finger mark
two primary classifications of characteristics to be found namely, ridge ending and bifurcations
bifurcation - ridges run parallel and split
there are variations of these two e.g. lake, independent ridge, spur and crossover
comparison examiners will assess holistically all r=features within a fingerprint
broken down into three levels of detail
basic print pattern
details described by Galton
configuration of sweat pores and shapes of ridges
5.6 comparison methodology
every feature is readily recognisable and identifiable and an identification can be made so long as there are sufficient characteristics of acceptable quality
match small amounts of friction ridges
a generic methodology for comparing fingerprints known as ACE-V has been adopted
one must first assess friction ridge detail in scene mark
comparison of mark features with reference print
evaluation of findings from which conclusions as to identify must be derived
element of peer review - verification that reaches same conclusions
during assessment examiner will look for:
distortion
development methods and medium used to visualize latent material
deposition pressure to highlight areas of possible distortion
anatomical attributes
clarity
during comparison examiner will look for similarities in:
pattern
ridge path
ridge shape
pore positioning
during evaluation examiner will form opinion on:
can mark be eliminated as belonging to suspect
is there sufficient info available to individualize
independent assessment carried to see whether ACE has been correctly carried out and whether conclusions reached are consistent with the original findings
two check approach
material finger marks found before compared against ten print cards
5.7 chemical composition of latent prints
latent finger mark is a complex mix of natural secretions of contamination from environment
three types of glands responsible for secretions of skin:
sudoriferous eccrine
apocrine glands
sebaceous glands
eccrine sweat made of salts, urea, sugars
palms of hands and feet produce only eccrine gland secretions
apocrine glands in groin/armpits generally open at hair follicles
sebacious glands are found on chest and back
secrete oil, the sebum, which protects skin and hair against water and acts as a lubricant
eccrine gland secretions are present in every latent fingerprint
contamination by sebaceous gland is very common
sebaceous material transferred onto hands by contact
5.10 chemical development techniques
Physical developer is silver based, and reacts with components within sebaceous sweat leaving silver deposit
usually used after DFO and ninhydrin treatments have concluded
time consuming and takes up human resources
45 mins to process an item of evidence as there are several individual processes within the overall treatment including immersion in acidic solutions and subsequent wash solutions
5.11 laboratory and scene applications
ninhydrin and DFO are effective treatments for items such as paper and cardboard and their use will be dependent on many factors
for example:
in optimum conditions DFO may prove more effective in enhancing latent material than will ninhydrin
ninhydrin is cheap and easy to use and produces easily visible finger marks
DFO is more costly and require light-source examination after the initial DFO treatment
both DFO and ninhydrin will react with blood and may be used to develop blood contaminated latent finger marks
DFO only recommended for use on paper and more porous surfaces for purpose of enhancing blood marks whereas ninhydrin can work equally well on non-porous
DFO (1,8-diazafluoren-9-one)
effective on paper and porous surfaces
reacts with amino acids and other components within latent finger mark, highly fluorescent and has pink/purple colouration
high intensity light sources must be used to augment this process
Ninhydrin
effective on paper and other porous surfaces
reacts with amino acids and produces immediate purple-coloured product
effective in conjunction with humidifier
caution when using
marks may develop after time
Superglue fuming (Cyanacrylate Vapour)
best applied in laboratory setting
best when item is too large or bulky or fragile for moving
health and safety
fluorescent dye (water based basic red 14) recommended for use at crime scene is less effective than alcohol based dyes such as basic yellow - try remove item
depends on correct environmental factors
80% humidity
120oC
for superglue
humidity enables chlorides present to take up water leading to polymerization
result is fibrous matted deposit
used on non-porous surfaces but examiner should use fluorescent dye to apply to deposits which under light source will highlight max no. finger marks
technique can interfere with other examinations
5.12 fingerprints in bodily fluids
most commonly in blood
fragile and easily damaged
enhancement techniques used in situ
photography and visual examination should precede any destructive enhancement process
dry print if wet
avoid using too high temperature as this could cause flaking or disintegration
direct photography is always preferable
on more porous surfaces DFO is very useful chemical treatment that will also react with any latent mark deposits from blood
as will ninhydrin
physical developer should also be considered after preceding treatments have been attempted
on non-porous latent material in bodily fluids are subject to different techniques
e.g. vacuum metal deposition could be considered - more sensitive than powders or superglue though limited to what can fit into vacuum chamber
so examination may progress to powders where visible material should be photographed post treatment but shouldn’t be lifted
Luminol can locate traces of blood, even if cleaned or removed
solution sprayed throughout area under investigation
iron present in blood catalyses chemical reaction leading to luminescence revealing location of blood
glow lasts for 30 secs and is blue
requires darkness
documented by long exposure photograph
drawbacks:
also fluoresces in presence of copper or alloy of copper, horseradish, bleach
luminol also detects small amounts of blood present in urine
distorted if animal blood is present in testing room
luminols presence may prevent other test from being performed on evidence
DAB (Diaminobenzidine)
used to develop latent prints and enhance visible prints that have been deposited in blood
applied by two methods:
submersion method
tissue method
cyanoacrylate fuming can be detrimental to all blood DAB processing must be completed before processing with cyanoacrylate
Acid Black 1, Acid Black/Amido Black
dye stain reacts with proteins in blood and other fluids
wont react with normal associated contaminants present in latent finger marj
Acid Violet 17, Acid Violet
also reacts with proteins in blood and other bodily fluids
gives fluorescent violet product
not react with normal associated contaminants in latent finger mark
can result on porous surfaces in production of uniform dark background colour
Acid Yellow 7, Acid Yellow
reacts with proteins in blood and other bodily fluids
gives yellow fluorescent product
doesnt react with normal associated contaminants
only used on non-porous as it cannot be removed from porous backgrounds, making it impossible to detect latent material