Goal #2 Objective B


Objective B:
Without the use of the course text or class notes, the student will identify how physical evidence can be a source of information.
In Objective A, evidence was identified to be:

"Anything that supports proof."

It was also noted there are three general categories of evidence


Let's look at the evidence that can be included in two of these categories (indirect and real evidence), physical evidence.

physical evidence -
Any object that can establish that a crime has been committed or can provide a link between a crime and its victim or a crime and its perpetrator.

Examples of physical evidence

Whether the evidence is immediately recognizable or needs to be analyzed, the investigator is trying to determine if the evidence establishes proof on different levels.

Generally, when physical evidence collected from a crime scene needs to be analyzed it goes to a police crime laboratory.

Lets look at the role forensic science plays in enhancing physical evidence as a source of information.

forensic -
Belonging to, used in, or suitable to courts of law or to public speaking or debate.

science -
A branch of study concerned with observation and classification of facts and especially with the establishment of verifiable general laws.

Let's link these definitions to define forensic science.

forensic science -
The application of science to those criminal and civil laws that are enforced by police agencies in a criminal justice system.

Public laboratories that conduct scientific analysis and interpretation are normally called crime laboratories.

Criminalistics is narrower in scope than forensic science. Forensic science can be applied to all criminal and civil laws, while criminalistics is applied to crime-scene physical evidence.

The forensic science conducted by crime laboratories is generally limited to criminalistics.
Therefore, the investigator who finds physical evidence at a crime scene must collect, package, and determine if laboratory analysis is necessary. When it is necessary, the evidence must be forwarded to the servicing crime laboratory.

The crime laboratory can attempt to identify the elements of the physical evidence, and if necessary compare unknown standards to known standards. These results can serve to link the suspect to the victim or crime scene, reconstruct the crime scene, or to clear an innocent person suspected of the crime.

The crime laboratory has several roles

When we say that "physical evidence is going to analyzed at the crime lab," there is a systematic procedure or plan the laboratory follows to make the physical evidence valuable as a source of information.

There are two areas of importance in the scientific analysis of physical evidence:

The purpose of identification, within the scope of physical evidence, is to determine the physical or chemical identity of a substance with as near absolute certainty as existing analytical techniques will permit.
Examples where identification of physical evidence is frequently used in forensic science

Why would identification of an illicit substance be important in forensic science?

Answer:
Because mere possession of illicit drugs is illegal. Therefore, an exact chemical analysis is necessary of suspected substances to convict a person of possession of a substance it is illegal to possess.

The same argument can be made for the sale of contraband. It must be established beyond a reasonable doubt that the substance being sold is in fact contraband.

How could identification of an explosive be important?
Answer:
In the case of the Oklahoma Federal Building Bombing, analysis of the explosive residue quickly changed the focus of the investigation from a foreign terrorist to a possible domestic act of terror.
Why?
Answer:
The analysis revealed that the explosive was made with, among other chemicals, animal manure. With the knowledge and experience the federal agencies had on terrorism, this was clearly the "signature" of a domestic act of terror.

How could identification of blood be important?
Answer:
It can distinguish human blood from animal blood. Therefore, blood found at a crime scene as physical evidence can be positively identified as human blood, to the exclusion of all other animal blood.

How could the identification of semen be important?
Answer:
The positive identification of the presence of semen can be an important piece of evidence in support of a victim's contention of an allegation of rape or other sexual misconduct.

How could the identification of hair be important?
Answer:
Species of origin can be determined with hair. In other words human hair can be distinguished from animal hair. This can be important when trace evidence is examined at the scene of a crime.

The average human loses hair daily, therefore hair found at the scene of a crime is critically important. Hair found at the scene may very well belong to the suspect, but first it needs to be identified as human.

The same can be done with wood. The species of origin can be identified.

The second area of importance to physical evidence we identified is comparison.

What does comparison mean?
Answer:
An analysis that subjects a suspect specimen [unknown] and a control specimen [known] to the same tests and examinations for the ultimate purpose of determining whether or not they have a common origin.

For example:
If the control standard was collected from the crime scene, a comparison analysis may show that the unknown standard did not originate at the crime scene and was not common with any control standard submitted.

If another control standard was removed from your suspect, and the comparison analysis shows a point of origin with your suspect, then your case may have just gotten much stronger.

As forensic scientists conduct comparisons they look for characteristics in unknown and known specimens.

What is a characteristic?
Answer:
Distinguishing trait, quality, or property.

When conducting a comparison analysis, forensic scientists compare unknown samples to known samples. As they compare samples, scientists look for properties that are similar and are not similar. In other words, they compare characteristics.

There are two types of characteristics used for identification purposes in a comparison analysis. They include:

individual characteristics -
Those identifiable characteristics that things share that share a common point of origin.

Fingerprints lifted from a crime scene, matched to fingerprints on a fingerprint card would be an example of individual characteristics.

Tool marks matched to a specific tool would also be an example.

class characteristics -
Those identifiable characteristics that things share with a group of items, when no common point of origin can be identified.

Examples of class characteristics include the classification of blood stains into blood types. Classification of paint scrapings from an automobile would be another type of class characteristics. General fingerprint pattern (whorls, loops, and arches) would be class characteristics.

The procedure or plan used by the criminalist to identify or compare for individual or class characteristics include:

contrast -
The degree of difference between the lightest and darkest parts (i.e. white powder on a black surface, etc.). Comparison of similar objects to set off their dissimilar qualities.

This is done most frequently with selecting a fingerprint dust that is a contrasting (or opposite) color to the color of the surface being fingerprinted.

Photography is another area where contrast can be altered.

The photographer can alter contrast by manipulating the

Usually contrast needs to be increased, but occasionally it must be reduced.

optical instruments -
Instruments that enhance the ability of the eye to see details through enlargement and clear resolution.

Example of optical instruments used in the crime laboratory

analytical instruments -
Instruments that furnish qualitative and/or quantitative details about a substance.

Two major classes of analytical instruments


destructive -
The analytical instrument consumes the sample during the test.

nondestructive -
The analytical instrument does not consume the sample during the test, leaving the sample available for further testing or for presentation in court.

Analytical instruments attempt to identify the elements of a substance. This is done by identifying the organic (contains carbon) or inorganic (no carbon content).

This begins the process for class and individual characteristics of a substance.

Examples of analytical instruments, type of substance screened for, effect on the sample and information on qualitative/quantitative findings can be found on page 40, Table 2.1.

Examples of organic and inorganic substances can be found on page 41, Table 2.2.

Osterburg identifies seven common clue materials for processing of physical evidence by a crime laboratory

Lets identify what the lab can do with these clue material.

Fingerprints -
Impressions of the friction ridges on the hands (fingers and palms) and feet(fingers and toes) on a surface. On the hand and feet, fingerprints facilitate gripping an object and the sense of touch. Fingerprints are formed on a fetus before birth.

Fundamental Principles of Fingerprints

Types of Crime-Scene Fingerprints

visible prints -
Prints made by fingers touching a surface after the ridges have been in contact with a colored material such as blood, paint, grease, or ink. Osterburg calls these environmental sources of fingerprints.

plastic prints -
Ridge impressions left on a soft material such as putty, wax, soap, or dust. Osterburg calls these environmental sources of fingerprints.

true latent -
Impressions caused by the transfer of body perspiration or oils present on finger ridges to the surface of an object. Osterburg calls these natural sources of fingerprints.

invisible prints -
(Same as "true latent" prints)

Visible and plastic prints can be located simply by looking.

Latent and invisible prints can be developed through application of chemicals, radiation or powder, depending on the hardness and porousness of the surface the print is on.

Latent fingerprint - controlling factors

Once a fingerprint is developed, it must be permanently preserved for future comparison and possible court evidence.

Methods of PreservationHistorical fingerprint classification and identification:
Evidence exists that the Chinese used fingerprints to seal legal documents over 3,000 years ago.

In the 1880, Henry Fauld suggested that skin ridge pattern could be important for the identification of criminals.

In 1892, Francis Galton published a book called Finger Prints, The first book of it's kind on the subject.

In the book Galton proposed assigning fingerprints to three pattern types

In 1897, Sir Edward Richard Henry proposed a fingerprint classification system to Scotland Yard. It was adopted and was later used in the United States as well.

Henry System -
Converts ridge patterns on all ten fingers into a series of letters and numbers arranged in the form of a fraction.

Using this classification system, all the fingerprint cards in the world could be divided into 1024 groups.

The first classification step is to pair up fingers, placing one finger in the numerator of a fraction, the other in the denominator.

Right Index----Right Ring----Left Thumb--Left Middle--Left Little
Right Thumb--Right Middle--Right Little---Left Index----Left Ring

The presence or absence of a whorl pattern is the basis for the determination of the primary classification.

If a whorl pattern is found on any finger



Any finger having an arch or loop pattern is assigned a value of 0.

After values for all ten fingers are obtained, they are totaled and one is added to both the numerator and denominator.

Approximately 25 % of the population falls into the 1/1 category. That is all their fingerprints have either loops or arches.

This system is used in the National Crime and Information Center computer in fingerprint classification information.

If an investigator has someone whose identity is in dispute, the investigator can check the "values" of the subjects fingerprints against what is listed in the computer. If they match, then they can be confirmed by pulling the fingerprint card. If they don't match, then it is likely the suspect is not who he says he is.

Firearm -
A weapon from which a shot is discharged by gunpowder.

When a firearm is discharged at the scene of a crime there is a variety of physical evidence potentially available.

Firearm investigative questions are outlined on page 78 by Osterburg.

Violent crimes in the United States are usually committed with firearms. Therefore, the focus of investigative attention is frequently on matching firearms to bullets or cartridges found at the scene of the crime.

When a link is established between a firearm and bullets or cartridges found at the scene of a crime, the person in possession of the firearm becomes an obvious suspect. If the person produces alibis for the weapon these must be checked.

The crime laboratory establishes a connection between firearms and their ammunition by using a comparison microscope.

The investigator who recovers a firearm must properly and accurately describe the weapon in the investigative report. If this is not accomplished, the weapon will later be ruled inadmissible.

The investigator should verify the operating condition of the weapon. Normally this is done at the crime laboratory, firing the weapon into a water recovery tank. The bullet and cartridge from that weapon can then be compared to the bullet and/or cartridge found at the crime scene.

When two or more bullets are fired at a crime scene a bullet trajectory can be established by sighting the bullet holes to their point of conversion (this is if the shooter remains stationary while shooting).

When investigating a crime of violence involving a firearm, the investigator should routinely have the laboratory check the integrity of the firing mechanism to determine if the firing mechanism could have accidentally discharged. This type of examination may eliminate such a defense for the suspect.

While checking the mechanical condition of the weapon, the trigger pull should be measured. Trigger pull can be determined by a crime laboratory with a firearms section by using a spring scale or adding weights to a pan scale hooked over the trigger. The trigger pull is determined with the firearm uncocked.

Most weapons manufactured in the United States have serial numbers. Firearm serial numbers can be useful to the investigator in determining ownership of the weapon since the weapon was manufactured. Frequently criminals attempt to file or grind the serial number off of the weapon. An etching process in the crime laboratory can restore the obliterated numbers.

During investigations involving firearms, the distance at which rounds were fired frequently becomes an issue. This can be significant in investigations involving suicides, self-defense claims, and where poor lighting made suspect recognition questionable.

The determination of shooting distance can be accomplished by viewing the smoke halo and powder pattern of the burned, partially burned and unburned powder particles blown from the muzzle of the gun when fired. This can be replicated by test firing the weapon from specified distances at material. Contrast or infrared photography can be used on dark material. Examples of this can be seen on page 82, Figure 2.17.

When a suspect is identified in a crime involving a firearm, particularly immediately following a crime, a neuron activation analysis (NAA) can be performed on the hands of the person suspected of firing the weapon. The test identifies the metal residue (barium and antimony) that come from the primer of the weapon when fired.

A NAA test can be used in the case of a suicide to determine if a firearm had been discharged in the hands of the deceased. If you are testing the hands of a suspect, either consent or a warrant should be obtained as this would be a search and seizure situation. More on search and seizure later in the course.

No test currently exists in the crime laboratory to determine when was the last time a firearm was discharged or how many rounds were discharged. The laboratory can only say a firearm was discharged since the last time it was cleaned.

The cartridge or bullet found at a crime scene can help investigators identify the caliber of weapon they are looking for, even before they find it. The markings on the butt of the case may also identify whether it was fired in a autoloader or revolver.

Violent crimes involving firearms where shots were fired, but lack casings on the ground are indicative of the possible use of a revolver.

Blood -
The fluid that circulates in the heart, arteries, capillaries, and veins of a vertebrate animal carrying nourishment and oxygen to and bringing away waste products from all parts of the body.
Websters New Collegiate Dictionary(1979)G & C Merriam Co:Springfield, MA

Blood is frequently found at crime scenes, particularly violent crimes.

Blood is one of the most perishable items of evidence at a crime scene, therefore it should be among the first items to be searched for and recovered at the crime scene.

Stains found at a crime scene may appear to be blood, but further laboratory analysis might show the stain to be rust, iodine, nail polish, or another liquid substance. Regardless, until you have a laboratory examination done, the stain must be treated as blood.

Characteristics of blood:


Before collecting blood, it should be photographed and marked on the crime scene sketch.

When blood is spattered, valuable insight can be gained through interpretation of the spots and patterns.

Blood patterns:
The location and shape of blood spots may indicate where the where the victim and assailant were during the crime. These locations may enhance the reconstruction of the crime.

If blood falls vertically onto a hard, smooth surface, the spots assume various shapes, depending on the height from which they fall.

The texture of a surface will have a slight effect on the blood spatter pattern.

If blood spatters against a vertical surface (i.e., wall, side of a vehicle, etc.), the pattern assumes a drawn out shape, depending on the angle it hits and the velocity it traveled before hitting the surface.

This information can assist the investigator with reconstructing the actions of the victim and assailant during a violent crime.

Blood is fairly easy to recognize when fresh, but as it dries its appearance can change. Additionally, blood that is painted over or washed away might go completely unnoticed unless suspicions are aroused. If this happens several presumptive field tests exist to determine the presence of blood.

Presumptive field tests


The investigator should be more concerned with the results of these tests rather than how they are performed.

Osterburg gives a list of practical results achieved through the examination of suspected bloodstains on page 85. He then goes into some detail explaining how each result was achieved. This is important reading for a prospective investigator.

The forensic laboratory can provide a great deal of information about your crime and suspect from the blood recovered.

The term serology is used to describe a broad scope of laboratory tests that use specific antigen and serum antibody reactions.

Questions the forensic scientist must answer when examining suspected dried blood

By analyzing the blood (the same can be done with semen and other body fluids)the lab can type the blood into one of four blood groups (O, A, B, AB), and the Rhesus (Rh) factor (+, -).

The four blood types & typical frequency distributions

A=42%
B=12%
AB=3%
O=43%


Continue to Goal #2 - Objective C.
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