Forensic Science - Fingerprints

What is examined in the 1st level of detail?

The overall complex pattern of ridges (loop, whorl, arch).

Can 1st level of detail be used for individualisation?

No, it can only narrow down possibilities.

What is examined in the 2nd level of detail?

Ridge characteristics, variations in ridge flow, scars, creases and subsidiary ridges.

Why is the coincidence sequence at the 2nd level of detail important?

It is unique to each fingerprint.

What is examined at the 3rd level of detail?

Individual ridge units including pore size, shape and relative position.

How are loops differentiated?

By the direction of their slope, ulnar or radial.

If a loop sloped to the left on the left hand or right on the right hand, what type is it?

Ulnar loop.

If a loop slopes right on the left hand, or left on the right hand what type is it?

Radial loop.

Where are deltas normally located on a fingerprint?

In the bottom half of the print.

How can deltas be positioned?

Offset to the left, right or on both sides.

What is the structure of a delta?

They always triradiate (3 branches).

What are the 2 types of arches?

Plain Arch and Tented Arch.

Describe a plain arch.

Ridges run side to side with no backward turn and no delta.

Describe a tented arch.

Ridges near the centre have an upward thrust, forming a tent-like shape.

What is the general shape of a whorl?

Circular or spiral pattern.

What is a central pocket loop?

A loop with a whorl at the end.

What is a double loop?

Two loops that create an “S-like” pattern.

What is an accidental loop?

An irregularly shaped loop pattern.

What is a ridge characteristic?

A deviation in the natural flow of the ridge.

What is a ridge ending?

When a ridge ends abruptly, and the parallel ridges come together to take its place.

What is a bifurcation?

When a single ridge forks into two, and other ridges diverge to make room for it.

What is a lake?

When a ridge bifurcates and rejoins itself shortly after, forming a lake within the ridge.

What is an independent ridge?

A small ridge situated between, but separate from the ridges on either side.

What is a spur?

A short section of ridge that branches off another ridge and ends in the space between two parallel ridges.

What is a crossover?

A short ridge that crosses the space between two parallel ridges, linking them together.

What must be identical for two impressions to come from the same finger?

Both the ridge characteristics and the coincident sequence.

What is a fingerprint?

The ridge pattern on the tips of the fingers, usually taken from a suspect.

What is a fingermark?

A deposit left on a surface in the pattern of the ridges when a fingertip touches it, usually found at a crime scene.

What are subsidiary ridges?

Smaller, finer ridges between main ridges. These are not always present and depend on the pressure exerted.

How should visible fingerprints be handled?

Photograph and recover them.

How should plastic fingerprints be handled?

Take casts, use a gel lifter or recover the article.

How should latent fingerprints be handled?

They need enhancing, either by powdering and lifting or recovering for chemical treatment.

What are visible fingermarks?

Contaminated impressions made by substances like blook, ink or grease.

What are plastic fingermarks?

Impressions left in a soft material such as wax, putty or dust.

What are latent fingermarks?

Caused by body perspiration and oils on the ridges, they are invisible and need development to be seen.

What are glass or carbon fibre brushed best for?

They cause the least damage to latent marks and are best for metallic flake powders.

What are metallic powders made of?

Commonly aluminium, but also bronze or gold.

What is a limitation of metallic flake powders?

Lifting may not be possible on old paint or difficult surfaces.

How should a granular powder colour be chosen?

Use a colour that provides the greatest contrast with the background.

What are magnetic powders used for?

Applied with a magnetic wand, useful on rough, grained or porous surfaces.

What are fluorescent powders?

Granular powders available in several colours that fluoresce under UV light.

When are fluorescent powders useful?

On rough, contaminated or multicoloured surfaces.

What type of surfaces are best for powdering?

Smooth, non-porous surfaces (glass, glazed pottery etc).

What powders are used on textured, non-porous surfaces?

Magnetic powders.

Name some non-porous substrates that are better suited to chemical treatments rather than powdering.

Polythene, cling film, wet items, aluminium cans.

What is ninhydrin used for?

Developing fingermarks on porous materials like paper or cardboard.

What is superglue used for?

Developing fingermarks on non-porous surfaces (e.g. bags, drug wraps, aluminium cans).

What materials can be used for fingerprint lifting?

Gel lifts, adhesive tapes, ESLA and casting compounds.