Forensic Investigations MIDTERM EXAMINATION

Jordibeltre56

Chapter05-PhysicalEvidence1.pdf

Home >Law homework help >Criminal homework help >Forensic Investigations MIDTERM EXAMINATION

Chapter 5:

Physical Evidence

• Almost anything can be physical evidence.

• The purpose of recognizing physical evidence is so that it can be collected and analyzed.

• It is difficult to ascertain the weight a given piece of evidence will have in a case, as ultimately the weight will be decided by a jury.

Purpose of Examining Physical Evidence

The examination of physical evidence by a forensic scientist is usually for:

• Identification to determine the physical or chemical identity of a substance.

• Comparison analysis subjects a suspect specimen and a standard/reference specimen to the same tests and examinations for the ultimate purpose of determining whether or not they have a common origin.

Identification

The object of an identification is to determine the physical or chemical identity with as near absolute certainty as existing analytical techniques will permit.

• The process of identification first requires the adoption of testing procedures that give characteristic results for specific standard materials.

• Once these test results have been established, they may be permanently recorded and used repeatedly to prove the identity of suspect materials.

• Second, identification requires that the number and type of tests needed to identify a substance be sufficient to exclude all other substances.

Common Types of Identification

Examples of what the crime laboratory may be used to identify:

1. Chemical composition of illicit drugs

2. Gasoline residues from debris of a fire

3. Explosive residues; for example, dynamite, TNT

4. Blood, semen, hair, or wood

Comparison

A comparative analysis has the important role of determining whether or not a suspect specimen and a standard/reference specimen have a common origin.

Both the standard/reference and the suspect specimen are subject to the same tests.

The Forensic Comparison Procedure

The forensic comparison is actually a two-step procedure:

1. Combinations of select properties are chosen from the suspect and the standard/reference specimen for comparison.

2. Once the examination has been completed, the forensic scientist must be prepared to render a conclusion with respect to the origins.

Role of Probability

• Simply defined, probability is the frequency of occurrence of an event.

• In flipping a coin, probability is easy to establish.

• With many analytical processes exact probability is impossible to define.

Classifying Characteristics

Individual Characteristics Evidence that can be associated to a common source

with an extremely high degree of probability is said to possess individual characteristics.

• In all cases, it is not possible to state with mathematical exactness the probability that the specimens are of common origin.

• It can only be concluded that this probability is so high as to defy mathematical calculations or human comprehension.

Individual Characteristics

Examples: • The matching ridge characteristics of two fingerprints • The comparison of random striation markings on bullets or tool

marks • The comparison of irregular and random wear patterns in tire

or footwear impressions • The comparison of handwriting characteristics • The fitting together of the irregular edges of broken objects in

the manner of a jigsaw puzzle • Matching sequentially made plastic bags by striation marks

running across the bags

Class Characteristics

Evidence associated only with a group is said to have class characteristics.

• Surprising to the inexperienced is the frequent inability of the laboratory to relate physical evidence to a common origin with a high degree of certainty.

• Evidence is said to possess class characteristics when it can be associated only with a group and never with a single source.

• Nevertheless, the high DIVERSITY of class evidence in our environment makes their comparison very significant in the context of a criminal investigation.

Class Evidence

Evidence is said to possess class characteristics when it can be associated only with a group and never with a single source.

Nevertheless, the high DIVERSITY of class evidence in our environment makes their comparison very significant in the context of a criminal investigation.

Value of Class Evidence

• One of the current weaknesses of forensic science is the inability of the examiner to assign exact or even approximate probability values to the comparison of most class physical evidence.

• For example, what is the probability that a nylon fiber originated from a particular sweater, or that a paint chip came from a suspect car in a hit and run?

• There are very few statistical data available from which to derive this information, and in a mass- produced world, gathering this kind of data is increasingly elusive.

Value of Class Evidence

• One of the primary endeavors of forensic scientists must be to create and update statistical databases for evaluating the significance of class physical evidence.

• Most items of physical evidence retrieved at crime scenes cannot be linked definitively to a single person or object.

• The value of class physical evidence lies in its ability to provide corroboration of events with data that are, as nearly as possible, free of human error and bias.

• Because of its DIVERSITY, the chances are low of encountering two indistinguishable items of physical evidence at a crime scene that actually originated from different sources.

Value of Class Evidence

• When one is dealing with more than one type of class evidence, their collective presence may lead to an extremely high certainty that they originated from the same source.

• Finally, the contribution of physical evidence is ultimately determined in the courtroom.

• Just as important, a person may be exonerated or excluded from suspicion if physical evidence collected at a crime scene is found to be different from standard/reference samples collected from that subject.

Crossing Over

Crossing over the line from class to individual does not end the discussions.

• How many striations are necessary to individualize a mark to a single tool and no other?

• How many color layers individualize a paint chip to a single car?

• How many ridge characteristics individualize a fingerprint?

• How many handwriting characteristics tie a person to a signature?

These are all questions that defy simple answers and are the basis of arguments.

Natural vs. Evidential Limits

There are practical limits to the properties and characteristics the forensic scientist can select for comparison.

• Modern analytical techniques have become so sophisticated and sensitive that natural variations in objects become almost infinite.

• Carrying natural variations to the extreme, no two things in this world are alike in every detail.

• Evidential variations are not the same as natural variations. • Distinguishing variations of evidential use from natural

variations is not always an easy task.

Forensic Databases

The Integrated Automated Fingerprint Identification System (IAFIS) is a national fingerprint and criminal history system maintained by the FBI and launched in 1999. It contains fingerprints for nearly 68 million subjects.

The Combined DNA Index System (CODIS) enables federal, state, and local crime laboratories to electronically exchange and compare DNA profiles. Launched in 1998, it contains 350,000 profiles in its forensic index from unsolved crimes.

Forensic Databases

The National Integrated Ballistics Information Network (NIBIN) allows firearm analysts to acquire, digitize, and compare markings made by a firearm on bullets and cartridge casings. Nearly 1.6 million items have been entered into the database and 34,000 hits have been recorded.

The International Forensic Automotive Paint Data Query (PDQ) database contains chemical and color information pertaining to original automotive paints. Contains information about 13,000 vehicles.

Forensic Databases

SICAR (Shoeprint Image Capture and Retrieval) is a shoeprint database. This product has a comprehensive shoe sole database (SoleMate®) which contains more than 22,000 footwear patterns.

A second database, TreadMate®, also has been created to house tire tread patterns. Currently, it contains 6,000 records

Forensic Palynology

Forensic palynology involves the collection and examination of pollen and spores connected with crime scenes, illegal activities, or terrorism. The microscope is the principal tool used in the field of forensic palynology.

The information gained from the analysis of pollen and spore evidence has many possible uses. It can link a suspect or object to the crime scene or the victim, prove or disprove a suspect’s alibi, include or exclude suspects, track the previous whereabouts of some item or suspect, or indicate the geographical origin of some item.

PowerPoint Presentation
Physical Evidence
Purpose of Examining Physical Evidence
Identification
Common Types of Identification
Comparison
The Forensic Comparison Procedure
Role of Probability
Classifying Characteristics
Individual Characteristics
Class Characteristics
Class Evidence
Value of Class Evidence
Value of Class Evidence
Value of Class Evidence
Crossing Over
Natural vs. Evidential Limits
Forensic Databases
Slide 19
Slide 20
Forensic Palynology