PHYSICAL EVIDENCE

PHYSICAL EVIDENCE Chapter 3

Physical Evidence • It would be impossible to list all the objects that could conceivably be of importance to a crime. • Almost anything can be _________________. • Although you cannot rely on a list of categories, it is useful to discuss some of the ________________types of physical evidence.

Physical Evidence • The purpose of recognizing physical evidence is so that it can be ______________ and ________. • 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 ___________________.

Blood, semen, and saliva _____________ Drugs Explosives ____________ Fingerprints Firearms and ammunition Glass ___________ Impressions Organs and physiological fluids ______________ Petroleum products Plastic bags Plastic, rubber, and other polymers Powder residues Soil and minerals _______________ Vehicle lights Wood and other vegetative matter Types of Physical Evidence

Purpose of Examining Physical Evidence • The examination of physical evidence by a forensic scientist is usually undertaken for _____________ or ______________purposes. • _______________has, as its purpose, the determination of the physical or chemical identity of a substance with as near absolute certainty as existing analytical techniques will permit.

Purpose of Examining Physical Evidence • A ______________________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 ______________ origin.

Identification • The object of an identification is to determine the physical or chemical ___________ with as near absolute certainty as existing analytical techniques will permit. • The process of identification first requires the adoption of testing _________________that give characteristic results for specific ____________materials.

Identification • Once these test results have been established, they may be permanently _______________ and used repeatedly to prove the identity of ______________materials. • Second, identification requires that the number and type of tests needed to identify a substance be ____________to exclude all other ________________.

Common Types of Identification • The _______________is frequently requested to identify the chemical composition of an ______________drug. • It may be asked to identify gasoline in residues recovered from the debris of a fire, or it may have to identify the _______________of explosive residues—for example, dynamite or TNT.

Common Types of Identification • The identification of blood, semen, hair, or wood are also very common and, as a matter of routine, include a _______________________________________

Comparison • A _________________________has the important role of determining whether or not a suspect specimen and a standard/reference specimen have a common origin. • Both the _________________and the _____________________are subject to the same tests.

Comparison • The forensic _____________ is actually a two-step procedure. • First, combinations of select properties are chosen from the suspect and the standard/reference specimen for _____________. • Second, once the examination has been completed, the forensic scientist must be prepared to render a conclusion with respect to the ________________.

Role of Probability • To comprehend the evidential value of a comparison, one must appreciate the role that ________________ has in ascertaining the origins of two or more specimens. • Simply defined, ______________is the frequency of occurrence of an event. • In flipping a coin, ______________ is easy to establish.

Role of Probability • With many analytical processes exact probability is _____________ to define.

Classifying Characteristics • ____________________ Characteristics • Evidence that can be associated to a common source with an extremely high degree of probability is said to possess individual characteristics. • ____________________ Characteristics • Evidence associated only with a group is said to have class characteristics.

Individual Characteristics • In _________ cases, it is not possible to state with mathematical ____________ the probability that the specimens are of common origin. • It can only be concluded that this probability is so _________ as to defy mathematical calculations or human comprehension.

_____________ 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

__________ Characteristics • Surprising to the inexperienced forensic scientist is the frequent inability of the laboratory to relate physical evidence to a _____________ origin with a high degree of certainty. • Evidence is said to possess class characteristics when it can be associated only _____________and never with a single source. • Here again, probability is a determining factor.

Class Characteristics • Nevertheless, the high diversity of class evidence in our environment makes their comparison very ____________ in the context of a criminal investigation.

Class Evidence • One of the current weaknesses of forensic science is the inability of the examiner to assign exact or even approximate _____________values to the comparison of most class physical evidence. • For example, what is the _____________that a nylon fiber originated from a particular sweater, or that a paint chip came from a suspect car in a hit and run?

Class Evidence • 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 ________________. • One of the primary endeavors of forensic scientists must be to create and update statistical _______________ for evaluating the significance of ___________physical evidence.

Class Evidence • Most items of physical evidence retrieved at crime scenes _________ be linked definitively to a single person or object. • The value of class physical evidence lies in its ability to provide _____________ of events with data that are, as nearly as possible, ________ of human error and bias.

Class Evidence • The chances are _________ of encountering two indistinguishable items of physical evidence at a crime scene that actually originated from different sources. • When one is dealing with more than one type of ________ evidence, their collective presence may lead to an extremely ________certainty that they originated from the same source. • Finally, the contribution of physical evidence is ultimately determined in the ____________.

Crossing Over • Crossing over the line from class to individual does not end the discussions. • How many ______________ 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 _______________ characteristics tie a person to a signature?

Crossing Over • These are all questions that __________ 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 ________________________ in objects become almost infinite. • Carrying natural variations to the extreme, no two things in this world are _________________________________.

Natural vs. Evidential Limits • ______________ variations are not the same as _________________variations. • Distinguishing variations of evidential use from natural variations is not always an easy task.

Using Physical Evidence • As the number of different objects linking an individual to a crime scene increases, so does the __________________ of that individual’s involvement with the crime. • Just as important, a person may be exonerated or excluded from _______________ if physical evidence collected at a crime scene is found to be different from standard/reference samples collected from _______________________.

Forensic _____________ • TheIntegrated Automated Fingerprint Identification System (IAFIS), a national fingerprint and criminal history system maintained by the ____________. • TheCombined DNA Index System (____________) enables federal, state, and local crime laboratories to electronically exchange and compare __________ profiles. • The National Integrated Ballistics Information Network (_________) allows ___________ analysts to acquire, digitize, and compare markings made by a firearm on bullets and cartridge casings.

Forensic Databases • The International Forensic Automotive _________ Data Query (PDQ) database contains chemical and color information pertaining to original automotive ___________. • SICAR (______________ image capture and retrieval) is a _____________ database.

Reconstruction • The method used to support a likely sequence of events by the observation and evaluation of physical evidence, as well as statements made by those involved with the incident, is referred to as _______________________.

Reconstruction • Crime-scene reconstruction relies on the ________________efforts of medical examiners, criminalists, and law enforcement personnel to recover physical evidence and to sort out the events surrounding the occurrence of a crime.

The Role of ________ Evidence • The physical evidence left behind at a crime scene plays a _____________ role in reconstructing the events that took place surrounding the crime. • Although the _____________ alone does not describe everything that happened, it can support or contradict accounts given by witnesses and/or suspects.

The Role of Physical Evidence • Information obtained from physical evidence can also generate _________ and confirm the reconstruction of a crime to a jury. • The collection and documentation of physical evidence is the foundation of a ____________________________.

Summing It Up • Reconstruction is a ___________ effort that involves putting together many different pieces of a puzzle. • The right connections have to be made among all the parts involved so as to portray the ___________________among the victim, the suspect, and the crime scene. • If successful, reconstruction can play a vital role in aiding a ____________to arrive at an appropriate ________________.

Summing It Up • The recognition, collection, and analysis of physical evidence is the _________________ to successful reconstruction, but only ___________ of the process.

PHYSICAL EVIDENCE