Fingerprints and Exhibits

A fingerprint is defined as "an impression of the friction ridges of all or any part of the finger" (SWGFAST, Glossary 07-28-2009 ver. 2.0).
The scientific authority referenced is the Scientific Working Group on Friction Ridge Analysis, Study and Technology (currently known as the Organization of Scientific Area Committees - OSAC).

Uniqueness of Friction Ridge Skin:
- Human friction ridge skin is characterized as unique.
- Palmar skin refers to the bottom of the hands, while plantar skin refers to the bottom of the feet.
- Each individual possesses a unique arrangement of friction skin, implying that no two fingerprints will be the same.
Persistence of Friction Ridge Skin:
- The friction ridge skin is persistent and does not change throughout an individual's lifetime, except in the case of injury.

Fingerprints are fully formed by the time a fetus is 6 months old.
Unrelated individuals of the same race exhibit minimal genetic similarity in their fingerprints.
Parent-child pairs have some similarity due to shared genetic inheritance, while siblings show a higher degree of similarity.
Identical twins present the highest genetic similarity.
The formation occurs as the basal layer of skin grows faster than both the outer epidermis and the inner dermis, causing the basal layer to buckle and fold into complex shapes.

Size and Coverage:
- Skin is one of the largest organs in the human body, covering approximately 1.5 to 2 square meters in an adult.
- About 0.08 square meters constitutes friction skin.
- Skin thickness varies with location: generally up to 2 mm (thickest on palms at 4 mm and thinnest on eyelids at 0.5 mm).

Container: Acts as a protective enclosure for skeletal and internal structures.
Sensory Input: Provides sensations of external conditions (heat, cold, wetness, etc.).
Waste Elimination: Facilitates waste removal (salts, amino acids, ammonia, and urea) through sweating, which also regulates body temperature.
Grip: Enhances the ability to grasp and hold objects.

Layers: Comprises two distinct layers:
- Epidermis (top layer)
- Dermis (bottom layer)
The generating layer of the epidermis, adjacent to the dermis, is responsible for forming new cells.

Fingerprint depositions are a complex mixture:
- Approximately 99% is water.
- The remaining 1% consists of organic and inorganic salts, amino acids, and fats.
The chemical composition of fingerprints changes over time; drying impacts visibility.
The likelihood of developing a print diminishes as time since deposition increases.

Level 1 - Pattern: Overall pattern of the fingerprint (e.g. arch, loop, whorl).
Level 2 - Ridge Characteristics: Including core, bifurcations, and deltas.
Level 3 - Pores and Ridge Edges: Details such as edge shapes, creases, etc.

Loop: Lines enter on one side, re-curve, and exit on the same side. Accounts for approximately 65% of fingerprints.
Whorl: At least one complete circuit; includes two deltas. Approximately 30% of prints.
Arch: Lines go in one side and out the other side, without deltas. Accounts for about 5% of fingerprints.

Features include pore position, edge shapes, creases, scars, and incipient ridges; these are not solely used for identification.
Incipient Ridge: An immature friction ridge, thinner than its surroundings.

Analysis: Initial step to assess suitability of the impression for comparison.
- Observing pattern and ridge characteristics; recording findings in examiner’s bench notes.
- If unsuitable, examination ceases here.
Comparison: Evaluating similarities and differences between the unknown impression and known prints.
Evaluation: Considering all observations to reach a conclusion regarding the identity or uniqueness of the prints.
Verification: An independent review of the analysis, comparison, and evaluation processes.

Types of Impressions:
- Latent: Not visible without development techniques.
- Visible: Readily observable without additional processing.
- Moulded: Retain three-dimensional shape (e.g. in wax or chewing gum).

Powdering: Application of powder on nonporous objects to reveal latent prints.
Chemical Processes: Used for porous surfaces.
Choice of development method is determined by the substrate type (porous vs nonporous).

Marking: Use a wax pencil or dry erase marker to circle prints; number with letters for clarity and scale.
Photographic Documentation:
- Capture overall, mid-range, and close-up photos of the print.
- Ensure that scales are included for size reference in close-ups.

Use a hinge lifter or tape to lift the print without creasing.
Place the edge on the surface, apply pressure, and lift when fully covering the latent print.

Provide case details and location sketches on the back of the lift card after fingerprint lifting.

Investigate how suspect approached (foot, vehicle, etc.), did they conduct surveillance?
Determine the entry point (door, window, etc.) and assess attempted entry points or damage.
Document footwear impressions or pry marks related to entries.

Collect exhibits in new, unused packaging to prevent contamination.
Use PPE (personal protective equipment) to prevent contamination, changing gloves frequently.
Different packaging must be used based on the type of evidence (e.g., guns in cardboard boxes, swabs in breathable containers).

Number exhibits with case details marked, maintain a detailed property report for court purposes.
All movements of exhibits must be tracked while under police custody.