CJ 2500 MOD 2 DB

Chapter 4 – Physical Evidence

Class Characteristics

When the characteristics of physical evidence are common to a group of objects or

persons, they may be termed class. Regardless of how thoroughly examined, such

evidence can be placed only into a broad category; an individual identification

cannot be made because there is a possibility of more than one source for the

evidence.

Individual Characteristics

Evidence with individual characteristics can be identified as originating with a

particular person or source.

Soil is the natural accumulation of earth materials, such as weathering rocks,

minerals, and decomposing plants, along with pollen.minerals, and decomposing plants, along with pollen.

1. Soil examinations can determine whether soils share a common

origin by comparing color, texture, and composition.

2. Although it is class characteristic evidence, the analysis of soil

evidence can help focus investigations and discredit alibis.

3. The pollen in soil or on plants and grass can also be very

significant in determining whether or not a suspect was at the scene.

Locating and Handling Soil Evidence

Soil evidence may be important when the suspect drives or walks on unpaved

areas, so that it is picked up by tire treads or the bottom of shoes and cuffs of

the pants. It may also be recovered in a number of other places, such as the

floor board of the subject's car or on articles in the trunk of his vehicle,

including shovels and blankets.

Preserving Shoe/Footwear Prints

Footwear prints may, or may not be readily visible. If they are not immediately

apparent, turn the lights off and search for them using a flashlight.

Comparing Shoe Print Evidence

SICAR is a software package which classifies, archives, and identifies shoe prints.

Preserving Footwear Impressions

As in the case with footwear prints, the location of footwear impressions should be

photographed as part of the general scene and then with a scale.

Preserving Shoe Impressions in Snow

Dental stone is also the preferred material for casting impressions in snow,

replacing the more difficult and time consuming process of using sulfur, which has to

be heated.

Photographs of footwear impressions at a crime scene

In the first photo only the impressions are shown

In a subsequent photo a ruler will be added to show sizes

Later casts will be made of the impressions

GLASS

Glass is important as physical evidence because of the frequency with which it is

encountered.

A. It is essential that the crime scene technician and investigator

understand the ways in which glass reacts to force.

B. Handling Glass Evidence

Tape should not be used to collect glass evidence and any processing for latent

prints is ordinarily done in the laboratory.

An important question often associated with motor vehicle accidents and hit-

and-run cases involves whether or not the lights of a suspect vehicle were and-run cases involves whether or not the lights of a suspect vehicle were

actually on, or energized. This is particularly important when the suspect

vehicle has been crashed or wrecked. Advances in lamp filament technology

now allow the investigator to determine this question.

Fibers are of greater value as evidence than are rootless hairs because they

incorporate such variables as material type, number of fibers per strand, number of

strands, the thickness of fibers and strands, the amount and direction of twists.

Several different parts of the body—such as palms, fingers, toes and the

soles of the feet—have friction ridges that can be used for a “fingerprint.”soles of the feet—have friction ridges that can be used for a “fingerprint.”

There are three broad categories of latent fingerprints:

1. Plastic prints are created when fingers touch against some

material such as a newly painted surface, the gum on envelopes and stamps,

oil films, explosives, thick layers of dust, edible fats, putty, and adhesive tape.

2. Contaminated/visible prints result after a finger, contaminated

with foreign matters such as soot, oils, face power, ink, and some types of

safe insulation, touches a clean surface.

3. Latent/invisible prints are associated with the small amounts of

body perspiration and oil that are normally found on the friction ridges.

Conditions Affecting the Quality of Latent Fingerprints

1. The surface on which the print is deposited.

2. The nature of the material contaminating the fingerprint.

3. Any physical or occupational defects of the person making the print.

4. How the object on which the prints appear was handled.

5. The amount of the contamination.

Methods of Developing Latent Fingerprints

There are numerous ways to develop latent prints. Five of these with which investigators should be familiar are:

1. Traditional Powders. Commercially prepared traditional powers come in a number of colors, including black, white, silver, red, and gray.

2. Fluorescent Powders. Low concentrations of some naturally occurring substances will cause a latent print to fluoresce or glow, under laser, alternative light, or ultraviolet illumination.

3. Chemicals. A variety of chemicals are used to develop and enhance latent prints.

a. Amido black:

b. Crystal violet:

c. Iodine:

d. Ninhydrin:

e. DFO

f. Small-particle reagent (SPR):

4. Superglue Fuming

5. Visualization under Laser, Alternative Light, and Ultraviolet Illumination

The term reflected ultraviolet imaging system (RUVIS) is the generic name for a

class of lighting and imaging systems that have been increasingly used in the past

several years.

Latent prints are such valuable evidence that extraordinary efforts should be

made to recover them.made to recover them.

Superglue fuming was developed in 1978 and its use rapidly spread. In this

photograph a portable superglue fuming chamber is used to process the inside and

the outside of the car. It is more efficient for processing larger objects.

Forensic dentistry is a specialty that relates dental evidence to investigation.

The teeth and facial bones are a major means of identifying skeletal remains

and have been used by anthropologists for many years.

Dental records include, but are not limited to, dental X-rays, dentagrams,

dental charts, prosthetic molds, and dental cases.

Investigators must be particularly alert to the possibility that bite-mark

evidence exists whenever they are working violent-crime and child-abuse

cases.

Dental records are very useful in helping to identify unknown persons who have

been the victim of fowl play or who have been reported simply missing.

At crime scenes, blood may be encountered in sizes from small drops to

large pools, in states ranging from fresh to dried, or somewhere in between large pools, in states ranging from fresh to dried, or somewhere in between

those points, and in as many places as we can name, including on floors,

walls, ceilings, clothes, weapons, the suspect's and victim's bodies, and the

exteriors and interiors of vehicles. Blood is very important in DNA analysis.

If blood at the crime scene is fresh and relatively uncontaminated, identifying

it as such is not difficult. Hemident can be used to do a preliminary field test

for the presence of blood.

These are common sources of blood and DNA evidence that investigators need to

be aware of in conducting crime scene searches.

Below shows the proper use of Hemident in a presumptive or preliminary

field test for blood.field test for blood.

Firearms evidence is commonly encountered in murder, aggravated assault,

robbery, rape, drug, kidnapping, and suicide cases.

The laboratory examination of firearms evidence may be able to provide the

answers to the following questions.

1. Was this bullet fired from this weapon?

2. What else can be learned from the bullet?

3. What determinations can be made from cartridge cases?

4. What miscellaneous determinations can be made by examination of

firearms evidence?

When a bullet passes through the barrel of a weapon distinctive scratches are

caused.caused.

These scratches can be compared to bullets fired through firearms in

question.

Identification is affected by the condition of the gun and of the bullets.

Loosely defined, a document is anything on which a mark is made for the purpose

of transmitting a message. A disputed or questioned document is one whose source

or authenticity is in doubt. Social security numbers are an important source of

identification in America.

Criminals often try to produce social security cards in order to assume new

identities.

Illegal aliens also often try to obtain fake social security cards.

There are three types of forgery:

a. A traced forgery is created by tracing over a genuine signature. A

forgery of this type can be tied to the original, or master, signatures if that

original signature can be located.

b. A simulated forgery is produced by the writer who learns to

mimic a genuine signature. It may or may not be possible to identify the

forger, depending on the extent to which the suspect’s normal handwriting

characteristics.

c. A freehand forgery represents the suspect’s normal handwriting,

with no attempt to mimic the style of the genuine signature.

There are several different methods used in order to identify questionable

documents. These include:

Photocopier examination

Paper examination

Age of documents

Burned or charred paper

Altered or obliterated writing

Writing instruments

mechanical-impression instruments

Typewriting