Fingerprints Flashcards
What are fingerprints?
Tiny ridges, whorls and patterns on the tip of each finger
What are the 4 types of fingerprints?
- Central pocket loop
- Double loop
- Accidental loop
- Plain
Features of fingerprints
- Loops
- Whorls
- Arches
1st Level Detail
- Pattern of ridges - loop, whorl, arch
- Not sufficient for individualisation but can exclude
2nd Level Detail
- Ridge characteristic - bifurcation, ending
- Scars, creases and subsidiary ridges
3rd Level Detail
- Individual ridge unit
- Pore sizes, shape, relative position
- Poroscopy
Define finger-mark
an unknown traces thats been left by a person on an object - the mark has a lesser quality impression which inc latent, partial, distorted etc
Define fingerprint
A print taken for identification
Types of Finger-mark
- Latent
- Plastic
- Visible (either postive or negative)
Latent finger-mark
- major source of fingermark evidence
- deposited by individual when its directly interact with a surface/object
Three types of gland found on the skin: Latent fingermark residue
- Eccrine: all over the body, highest density on palms and soles (predominant component)
- Sebaceous: localised to regions inc hair follicle and the face + scalp (touching other parts of the body)
- Apocrine: found in the axillary regions (armpit + groin) least contributon
Latent fingermark composition
The chemical composition of the mark found at a crime scene depends on
- Original mark
- Surface
- Age/ time since deposition
- Storage condition e.g. temp, light, water exposure etc
Forensic Evidence recovery (Initial assessment)
Type of item/surface
Condition of item/surface
History of item/surface
Presence of other forensic evidence type
Forensic Evidence recovery (Outcome of initial assessment)
- Suitable for forensic evidence?
- Suitable for fingermark recovery only?
- Suitable for “ “ and other forensic evidence
Forensic Evidence recovery (Forensic evidence recovery strategy/plan)
- Constraints and limitation
- Force policies and or priorities
Purpose of visualisation and enhancement
- Enhance of the ridge detail, minutiae
- To provide contrast between the ridges and the background
- Improve the chance of making an identification
How can it be achieve? (visualisation and enhancement)
- Visual examination (lighting)
- Chemical enhancement tech
those which react with components e.g ninhydrin - Physical enhancement
those which detect the greasy nature of the surface e.g powder - Digital enhancement
Visual examination
- Visible lighting (inc diffuse, oblique, ring light)
e.g all types of fingermarks - Fluorescence examination e.g latent fingermarks (sweat, oil, grease, contaminated finger-marks on a fluorescent surface, enhance finger-marks)
- Specialist lighting e.g infrared reflection (metallic/inorganic deposition process) , ultraviolet reflection, multi spectral imaging
Advantages and Disadvantages of visual examination
A: Non destructive, can be low tech, can be easy to carry out
D- Depends on the fingermark, can be high tech, difficult to carry out and record image
Must be carried out before, during and after treatments
Chemical/Physical enhancement
Sebaceous material
Eccrine material
How to treat exhibits?
- Chemical and physical characteristic of a mark generally not known
- Resulting mark arises from interaction between the mark, the substrate and environment: difficult to predict an individual case
- Difficult to determine the age of a mark; many variable to take into account
Triangle of interaction
Finger-mark composition
- Natural, eccrine-rich, sebaceous-rich, a contaminant present e.g blood, grease
Surface
- Texture, elasticity, rigidity, size, shape, condition, type of surface, material of surface
Environment
- Temp, humidity, exposed to water/other chem
Fingermark enhancement
A process of forming a new image quality using various techniques + methods to obtain images that are more easily interpreted by the human eye
