L4-5: fingereprint identification Flashcards
describe volar pad formation [6-12 weeks fetus]
6 weeks
- hand is shaped like a paddle
- volar pads can be seen
8 weeks
- fingers separate
10 weeks
- digital pads are distinct
12 weeks
- friction ridges start to develop in basal layer of epidermis
- volar pads start to regress
4 premises of friction ridge skin
- friction ridges develop on the fetus in their definitive form prior to birth [embryology]
- friction ridges are persistent throughout life except for scarring, disease, or decomposition after death [histology]
- friction ridge paths and the details in the small area of the friction ridges are unique and never repeated [uniqueness]
- friction ridge patterns vary within limits therefore allowing for classification [classification, identification and exclusion]
another word for the bertillon system
bertillonage or anthropometry
describe the bertillon system
- alphonse bertillon [1853-1914]
- devised a method of personal identification through a series of body measurements
- full face and profile photographs of perpetrator now commonly known as mugshots in criminal cases
- head length and breadth, finger and foot measurements, eye and hair colour, weight, complexion, a single fingerprint
flaws with bertillon system
characteristics being measured are dynamic and can change, therefore are not 100% reliable
- young offender, not full grown
- repeat offenders, changing appearance and name
- human error in performing measurements
what did sir francis galton contribute to the history of fingerprint identification
- first to define and name specific minutiae known as ‘galton details’
- responsible for the acceptance of the use of fprints for personal identification
- suggested system of ID by means of a record of fprints only
what was the result of the troup committee when looking at the bertillon system and galton’s suggestion of fingerprint ID
- 1893
- bertillon system and fingerprintts were considered effective
- fprints did not have a classification system
- committee decided to implement both systems
5 major anthropometric measurements to be taken for primary classification, and fprints to be attaches as an additional component to the classification system
what did sir edward henry contribute to the history of fingerprint identification
- developed a classification system for fingerprints
- henry classification system
when/how did fingerprints as a means of identification become a standard practice in england [belper committee]
- belper committee [1900]
- recommended that all criminal ID records be classified by the fprint system
- the henry classification system and the individualization of criminals by means of fprints became a standard practice
describe 4 different volar pad development + fprint pattern configurations
- high & narrow vp –> whorl fp
- intermediate volar pad with steep radial side –> ulnar loop fp
- intermediate volar pad with steep ulnar side –> radial loop fp
- low & broad vp –> arch fp
factors that influence friction ridge skin formation
- shape and size of volar pad
- flow of the ridges follow the curvature lines of the skin on the volar pad - timing
- between the regression of the volar pads and the onset of the friction ridges - relative speed of the 3 developmental fronts
- genetics say that friction ridges must cover the entire surface
- develop at different speeds - genetics/diseases
- familial similarities
friction ridge skin characteristics
- referred to as volar skin
- seen in palmar and plantar surfaces
- seen in primates
- sweat glands only [no sebaceous glands]
- more sweat glands per square inch than other skin areas
- no hair
- lack of pigmentation
- each individual f.ridge unit has one sweat gland and one pore
- skin made up of 2 layers – dermis, epidermis
attributes:
- assists in ability to hold things [grip]
- provides traction to mitigate slippage
- sensory input [abundance of nerve endings]
- waste elimination through sweat glands
- thickness – must withstand daily gripping, lifting, touching, etc. [otherwise would be painful due to nerve endings]
2 layers in skin structure [L4:27…]
dermis
- thick foundation layer
- 15-40x thicker
epidermis
- cornified thin outer layer
- 15-20 layers of flat dead cells that are regularly shed through abrasion and replaced by regeneration
epidermis layers [young to old]
- basal layer
- spinous layer
- granular layer
- hyalin layer
- horny layer
[Basal’s Spinning Grandma is High [hy] and Horny]
describe the basal layer
- ‘generating layer’
- cells created in this layer migrate up towards the top layer
- cells typically flatten as they migrate to the top layers
- eventually once cells reach the top they slough off of dead skin cells
- cycle typically takes 30 days to complete
what are desmosomes
skin cells are connected through cell junctions called desmosomes
desmosomes release and reattach as needed during migration
what effects the persistency of friction ridge skin
injury, disease, and body decompostion
what happens when an injury damages or penetrates the basal layer
may destroy its ability to regenerate cells in that damaged area
surrounding cells can generate, but the deformation will result in the formation of a scar on the surface
what happens if an injury damages thee top layers of the epidermis
the skin will repair itself and friction ridge skin would gradually return to normal
how does body decomposition affect friction ridge skin persistence
- no new skin growth
- skin is less stable
- friction ridges simply degrade with the decomposition of the body
dyplasia effects on friction ridge persistency
- disease
- normal cells undergo abnormal changes
- may or may not be cancer
first level details of friction ridge skin
overall patterns
- loop
- whorl
- arch
describe loop patterns
- ridges flow in from one side, re-curve, flow out in the same direction
- a core and a delta
- common rating: 65%
what is an ulnar loop
- subcategory of a loop
- flow of ridges enter and exit towards the little finnger
what is a radial loop
- subcategory of a loop
- flow of ridges enter and exit towards the thumb
describe whorl patterns
- has at least one ridge in the middle making a complete circle [spiral, oval, or circle]
- a core and two deltas
- common rating: 30%
subcategories of whorl patterns
- double loop whorl: consists of 2 separate loop formations and 2 deltas
- central pocket whorl: combination of a loop and a whorl pattern
- accidental whorl: 2 or more deltas with 2 or more distinct types of patterns - essentially random
describe arch patterns
- ridges enter on one side and flow out the other side
- no core or deltas
what is a tented arch pattern
- subcategory of arch patterns
- ridges in the center form a definite angle
second level details of friction ridge skin [L4:47]
- referred to as minutiae
- major ridge path deviations
- ridge endings
- bifurcation
- dot
- island [short ridge]
- lake [enclosure]
- bridge
- hook [spur]
- opposed bifurcations
- ridge crossing
- opposed bifurcation ending
third level detail of friction ridge skin
size and shape of pores and ridges
- end shapes and angles
- adjacent ridge formation
- ridge width
- pores
factors that influence uniqueness of friction ridge skin
incipient ridges – ridges that did not fully develop [may not have a pore]
creases/voids
dysplasia – ridge units are present but do not fuse together, appears dotty
uniqueness of friction ridge skin
- uniqueness relies on differential growth occurring at different times and speeds while being subject to both genetic and physical forces during fetal development
- f.ridge skin is made up of individual ridge units
- all ridge units vary in shape, size and alignments but grow in concert to cover entire surface area of volar pad
- each ridge unit contains one sweat gland and one pore opening
- pore openings are established at random
can exclusions or identifications occur at first level details
only exclusions can occur
can exclusions or identifications occur at second level details
exclusions and identifications can occur
can exclusions or identifications occur at third level details
exclusions and identifications can be supported
types of crime scene impressions
- latent
- patent
- deposit
- take-away
- plastic/mould
latent impressions
- not visible to the naked eye
- require development technique to be visible
- may be visible under oblique lighting prior to development
patent impressions
- do not require development
- visible under normal circumstances
- photographed in-situ as is
- mostly are 2-D and made up of some foreign materials [blood, dirt, oil, grease, paint]
deposit impressions
- transferring material from hand to another object
- majority of impressions found are deposit impressions
- good to compare to takeaway impressions
- consist of bodily secretions - latent impressions
- consist of foreign material - patent impressions
take-away impressions
when the friction ridge skin removes material from a surface
- ex. touching something dusty [taking away dust] – voids in print are where your f.ridges are
plastic or mould impressions
- 3-D patent impression
- typically only photographed, may be preserved with casting material
- ex. print left in melting chocolate bar
what type of impressions are majority of impressions that are found
deposit impressions
what are 5 steps to collect fingerprint impressions
- develop/locate
- label
- photograph
- document
- preserve
developing and locating f.print impressions
powder the surface and circle each impression as you locate it
considerations when collecting fingerprint impressions
substrate, matrix
- ex. for a porous substrate such as paper, powder cannot be used, so a chemical techique would be used]
different powders
- granular powders – white, grey/silver, black
- magnetic powders – black
- metallic powders
- fluorescent powders
- advanced chemical developments
most widely used powder for developing f.prints
granular powders
using granular powders
- easily transportable
- white/black powders to provide contrast
- works on variety of non-porous surfaces
- used in combination with a fibreglass tip brush
- become airborne easily, messy
- cautious of overpowdering
what brush are granular powders used in combination with
fibreglass tip brush
why are fibreglass tip brushes used with granular powders
- does least amount of damage, while carrying most amount of powder
- able to cover more of surface before needing to recharge
- brush is made of nylon
using magnetic powder
- contains iron particles and granular powder
- iron carries powder
- applied using a magnetic wand
- clean – only powder touches the surface, no chance of damaging impression from brush
- should not be used on surfaces that may be magnetized
caring for granular powders
- can be contaminated by moisture/foreign material
- stored in airtight containers
caring for magnetic powders
magnetic powders will eventually lose their effectiveness
- lose its ability to hold its charge
properly labelling f.print impressions
- circle impression with china marker - include R# and a directionality arrow if necessary
- label scales and place appropriately:
- GO# [general occurence #]
- date
- badge
- R#
- location [where print was found]
purpose of a directionality arrow when labelling
indicates upwards
used on vertical surfaces only
purpose of R# when labelling
- reference number that each lift is assigned [R1, R2, R3,..]
- an upper case R cannot be reversed and the orientation is easily established
properly photographing fingerprint impressions
- overall photo – showing item in the scene, location shot
- midrange – showing the impression/item in relation to the scene
- closeup up – fill the entire frame with the impression, take photos with and without scale
properly documenting fingerprint impression evidence
make notes in memo book including location, R#, diagrams, measurements
properly preserving fingerprint impressions
- after impressions have been located, developed, labelled, and photographed, and documented, they can be preserved
- preserved by lifting impression with clear adhesive lifting tap, then placing tape on latent print card
- info on back of card is filled out, diagram is drawn
