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PHYSICAL EVIDENCE. Chapter 3. Physical Evidence. Almost anything can be Physical Evidence. Although you cannot rely on a list of categories, it is useful to discuss some of the most common types of physical evidence. Types of Physical Evidence. Blood, semen, and saliva Documents Drugs
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PHYSICAL EVIDENCE Chapter 3
Physical Evidence • Almost anything can be Physical Evidence. • Although you cannot rely on a list of categories, it is useful to discuss some of the most common types of physical evidence.
Types of Physical Evidence • Blood, semen, and saliva • Documents • Drugs • Explosives • Fibers • Fingerprints • Firearms and ammunition • Glass • Hair • Impressions • Organs and physiological fluids • Paint • Petroleum products • Plastic bags • Plastic, rubber, and other polymers • Powder residues • Soil and minerals • Tool marks • Vehicle lights • Wood and other vegetative matter
Purpose of Examining Physical Evidence Two Methods • The examination of physical evidence by a forensic scientist is usually undertaken for identification or comparison purposes. • Identification • the determination of the physical or chemical identity of a substance • A comparison analysis subjects a suspect specimen and a standard/reference specimen to the same, ultimate purpose of determining whether or not they have a common origin.
Identification • Once these test results • 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 • The crime laboratory is frequently requested to identify the chemical composition of • an illicit drug. • gasoline in residues recovered from the debris of a fire, • nature of explosive residues—for example, dynamite or TNT. • blood, semen, hair, or wood are also very common • include a determination for species origin.
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.
Comparison • The forensic comparison is actually a two-step procedure. • First, combinations of select properties are chosen from the suspect and the standard/reference specimen for comparison. • Second, once the examination has been completed, the forensic scientist must be prepared to render a conclusion with respect to the origins.
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. • Class Characteristics • Evidence associated only with a group is said to have class characteristics. Exp. Paint/fibers
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 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 • Value of class evidence: - corroborate events with data - minimum human error/bias • Finally, the contribution of physical evidence is ultimately determined in the courtroom.
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.
The Role of Physical Evidence • The physical evidence left behind at a crime scene plays a crucial role • in reconstructing the events that took place surrounding the crime. • it can support or contradict accounts given by witnesses and/or suspects. • generate leads and confirm the reconstruction of a crime to a jury. The collection and documentation of physical evidence is the foundation of a reconstruction.
Summing It Up • Reconstruction is a team 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 relationship among the victim, the suspect, and the crime scene. • If successful, reconstruction can play a vital role in aiding a jury to arrive at an appropriate verdict.
Summing It Up • The recognition, collection, and analysis of physical evidence is the foundation to successful reconstruction, but only part of the process.
Forensic Databases • A computerized archive of information relating to a specific type of physical evidence contains manufacturers • Fingerprint • CODIS (DNA profiles) • Ballistics (recovered) • Automotive paint data • Shoeprint
Case Study • JonBenet Ramsey Page 43 • 1) Read the case • 2) What type of evidence would you look for? • 3)How would you secure and process the scene? • 4) How do you think the investigators erred in this case?
