exam 2 forensics

when are fingerprint ridges formed

during fetal development

do people have the same fingerprints

no, not even identical twins have the same fingerprints

3 fundamental principles of fingerprints

First fundamental principle

a fingerprint is an individual characteristic; again, no two people have been found with the exact same fingerprints

3 fundamental principles of fingerprints

Second fundamental principle

a fingerprint pattern will remain unchanged for the life of an individual. only permanent scarring or disease can alter the print

3 fundamental principles of fingerprints

Third fundamental principle

fingerprints have general characteristics ridge patterns that allow them to be systematically identified

latent fingerprints

not apparent to the naked eye

are formed by sweat and oils on the skin that are deposited when touching a surface

must be developed before they can be seen

made visible by dusting, fuming, or using chemical reagents

fingerprint patterns

what are they and how much of the population has them?

loops (60-65% of the population)

whorls (30-35% of the population)

arches (seen in 5% of the population)

arches

arches are the simplest type of fingerprints that are formed by ridges that enter on one side of the print and exit on the other. no deltas are present

types of arches

plain: ridges enter on one side and exit on the other side

tented: similar to the plain arch, but has a spike in the center

loops

these must have one delta and one or more ridges that enter and leave on the same side

whorls

have at least one ridge that makes (or tends to make) a complete circuit. they also have at least two deltas.

types of whorls

plain whorl

central pocket loop (whorl)

double loop (whorl)

accidental whorl

processing latent prints

they can be seen, collected, and compared

that is called either development, enhancement, or visualization

collecting fingerprint evidence

1. prints must be located

2. visual and impressed prints are the easiest to locate

3. they can be photographed, lifted using tape (visual prints), or other means, or the impressed object itself can be collected as evidence

latent prints

Where are they located and on what type of conditions

they can be located on different types of factors; light conditions, the surface, and other factors

processing steps with regular fingerprint powders

1. Photograph any visible fingerprints that you observe.

2. Carefully dip the brush into the appropriate powder. Apply a small amount of powder to the tip of the brush.

3. Apply the powder to the surface with a light twirling motion over the area to be processed. If a heavy deposit appears on a fingerprint, gently brush off the excess powder with a light twirling motion.

4. Photograph any latent fingerprints that have been developed.

5. Apply a short piece of lifting tape. This must be pressed well onto the surface.

6. Slowly remove the lifting tape from the surface and place it on a backing card that is of contrasting color to the powder being used.

7. Properly fill out the back of the backing card with the proper information

impression evidence

2d and 3d impressions

2D impressions: are found on hard surfaces where the impression is only on the surface (like a fingerprint)—often blood, mud/dirt, or grease

3D: are in a material that gives under the pressure of a person’s weight (like sand, dirt, snow, etc.)—foot/shoe print, tire tracks

What must you do before doing anything?

photograph!

Collecting impression evidence:

what is recommended to do, if possible

cut out or take item with impression on it to be analyzed

how can 2D impressions be collected

it could MAY BE able to be lifted like fingerprints

how can 3D impressions be collected

casting—by using a putty or plaster like substance to fill in the impression and lifting it whole

association of firearms and tool mark examiners def:

an object used to gain mechanical advantage

the harder of two objects which, when brought into contact with each other, results in the softer one being marked

toolmark types:

compression/indented

when tool is pressed into a softer surface

often show outline of tool’s working surface (i.e., hammer head or jaws of pliers)

tookmark types:

abrasion/sliding/scraping

edge of tool moves along a surface

produces a series of striations that match the profile of the tool edge

toolmark types:

cutting

associated with cutting padlocks or chains

tool edge will determine the resulting appearance of the cut

class characteristics of toolmarks

determine what type of tool, possibly even specific tool, based on measurements of toolmarks found at scene or matching tool to the toolmark

individual characteristics of toolmarks

comparing toolmarks under microscope with possible object that caused harm

use suspect tool to make marks on a reference surface (usually soft lead) and compare to toolmarks found at scene

collecting toolmark evidence

how to package

if possible, package the entire object for examination at the labratory

collecting toolmark evidence

what to do if object can’t be moved

photograph in detail with scale

how to collect the impression

use Mikrosil type putty

important!!

make sure to review lab notes :)