forensic fact story

fingerprints

Principle of fingerprints->

1st principle->

A fingerprint is an individual characteristic; no two fingers have yet been found to possess identical ridge characteristics.

2nd principle->

A fingerprint will remain un-charged during an individual's lifetime.

3rd principle->

Fingerprints have general ridge patterns that permit them to be systematically classified.

Loops->

A loop must have one or more ridges that enter from one side of the print, re-curve, and exit the same side.

One delta/one core

Whorls->

One or more cores

At least two deltas

Arches->

An arch is formed by ridges entering from one side of the print, rising slightly and exiting on the opposite side.

No deltas/no cores.

Classes of fingerprints->

Plain arch->

The simplest of all fingerprint patterns; a plain arch is formed by ridges entering from one side of the print, rising slightly and exiting on the opposite side.

Tented arch->

A tented arch rises sharply upward causing the center of the print to look like a tent.

By definition, the angle of the lines on a tented arch meets at less than a 90-degree angle.

Ulnar loops->

An ulnar loop opens the little fingerprint from the right.

Radial loops->

A radial loop opens towards the thumbprint from the right.

Whorls->

One or more cores

At least two deltas

Plain whorl->

At least one ridge that makes a complete circuit.

The ridge may be in the form of a spiral, oval, or any variant of a circle.

If an imaginary line is drawn between the two deltas contained within the pattern and the line does not touch any of the spiral ridges, then the pattern is a plain whorl.

Two deltas

One core

Displays a degree of sympathy

Double loop->

A double loop is made of two loops combined into one fingerprint.

Two deltas

Two cores

Appears to have an "S" in the print

Accidental->

All other prints

Fingerprint shapes->

Arches

Loops

Whorls

Reading fingerprints->

Reading prints->

The key to reading prints is not to find each character in the prints, but to get the trend of patterns.

Most prints found at a crime scene are partial prints that rarely contain all deltas and cores.

We must learn to look at the trend and of the lines as a whole, rather than individual lines.

Double loops->

Contain an "S" shape within the print

Plain whorls/central pocket loops->

These are the only prints that contain a circle or spiral within the print.

Plain whorls have symmetry core in the center, deltas near the bottom of the print.

One of the deltas on CPL will be twisted and closer to the core( no symmetry).

Arches->

All lines enter at one side of the print and exit the other

Loops->

These prints have some lines that enter on one side, turn, and then exit the same side.

Fingerprints->

Visible prints are made after coming in contact with colored material such as blood, paint, grease, or ink.

Plastic prints are ridge impressions left on a soft material such as putty, wax, soap, or dust.

Latent prints( invisible prints) are impression caused by the transfer of body perspiration or oils presentation on the finger to the surface of an object.

Latent prints must be developed or made invisible.

Dusting->

Appropriated surface->

Ridged/non-porous such as glass, plastic, or metal.

Theory->

Dust will adhere to sweat and oils left behind.

Iodine fuming->

Appropiated surface->

Porous and non-porous such as paper, index cards, magazines, and cardboard.

Theory->

Sweat and oil will absorb iodine vapors.

Ninhydrin->

Appropriate surface->

Porous such as paper, tissue, and clothing.

Theory->

Ninhydrin reacts with amino acids to form a purple compound.

Silver nitrate and ultra-violet light->

Appropriate surface->

Porous such as paper or drywall

Theory->

When exposed to ultra-violet (UV) light, silver nitrate reacts with the salt in sweat to form a blackish-brown compound.