Download - Fs Ch 5
Physical Evidence
Chapter 5
Forensic ScienceRichard Saferstein
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.2
Physical Evidence
Almost anything can be physical evidence
Important to recognize physical evidence is so that it can be collected and analyze
Difficult to ascertain weight of piece of evidence in court
-ultimately decided by a jury
Forensic ScienceRichard Saferstein
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.3
Purpose of Examining Physical Evidence
Identification:-determination of the physical/chemical
identity of a substance with as near absolute certainty as existing analytical techniques will permit
Comparison: -subjects a suspect specimen and a
standard/reference specimen to the same tests and examinations to determine if they have a common origin
Forensic ScienceRichard Saferstein
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.4
IdentificationPROCESS:
-adoption of testing procedures that give characteristic results for specific standard materials
-test results have been established-permanently recorded-used repeatedly to prove the identity of suspect
materials.-requires number/type of tests needed to identify
a substance exclude all other substances
Forensic ScienceRichard Saferstein
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
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Common Types of Identification Illicit drugs
Gasoline in residues
Explosive residues
Identification of blood/semen/hair
Forensic ScienceRichard Saferstein
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
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Comparison Comparative analysis:-if suspect specimen and a standard/reference
specimen have a common origin-standard/reference and suspect specimen subjected
to same tests
2 step procedure:-combinations of select properties are chosen from suspect and
standard/reference specimen for comparison-be prepared to render a conclusion with respect to the origins
Forensic ScienceRichard Saferstein
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.7
Role of Probability
To comprehend the evidential value:-must appreciate the role that probability has
in ascertaining the origins of two or more specimens
Probability:-frequency of occurrence of an event Exact probability is impossible to define in
many analytical processes
Forensic ScienceRichard Saferstein
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.8
Classifying Characteristics
Individual Characteristics-Evidence associated to a unique
source with high degree of probability
Class Characteristics-Evidence associated only with a
common source
Forensic ScienceRichard Saferstein
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.9
Individual Characteristics
Not possible to state with mathematical exactness the probability that the specimens are of common origin
-Can only be concluded that this probability is so high as to defy mathematical calculations or human comprehension
Forensic ScienceRichard Saferstein
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.10
Individual Characteristics Examples:
the matching ridge characteristics of two fingerprints
random striation markings on bullets/tool marks Irregular/random wear patterns in tire/footwear
impressions handwriting characteristics sequentially made plastic bags by striation
marks running across the bags
Forensic ScienceRichard Saferstein
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.11
Class Characteristics Surprising to the inexperienced forensic
scientist 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.
Here again, probability is a determining factor. Nevertheless, the high diversity of class
evidence in our environment makes their comparison very significant in the context of a criminal investigation.
Forensic ScienceRichard Saferstein
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.12
Class Evidence Weaknesses of forensic science:-inability to assign exact/approximate
probability values to the comparison of most class physical evidence
Very few statistical data-available from which to derive this
information-mass-produced world
Forensic ScienceRichard Saferstein
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
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Class Evidence Primary endeavor:-create and update statistical databases
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.
Forensic ScienceRichard Saferstein
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.14
Class Evidence Chances are low of encountering two
indistinguishable items of physical evidence at a crime scene that actually originated from different sources
More than one type of class evidence may lead to high certainty that they originated from the same source.
Contribution of physical evidence is ultimately determined in the courtroom.
Forensic ScienceRichard Saferstein
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.15
Crossing Over 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 defense lawyer arguments
Forensic ScienceRichard Saferstein
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.16
Natural vs. Evidential Limits
Practical limits to properties/characteristics for comparison:
-Modern analytical techniques are so sophisticated/sensitive that natural variations in objects become almost infinite
-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 ScienceRichard Saferstein
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.17
Using Physical Evidence
Number of different objects linking an individual to a crime scene increases:
-likelihood of that individual’s involvement with the crime
-exonerated/excluded from suspicion if physical evidence is different from standard/reference samples collected from that subject
Forensic ScienceRichard Saferstein
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
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Forensic Databases• Automated Fingerprint Identification System (IAFIS):-fingerprint and criminal history system (FBI)
• Combined DNA Index System (CODIS):-electronically exchange and compare DNA profiles
• National Integrated Ballistics Information Network (NIBIN):-acquire/digitize/compare markings made by a firearm on bullets and
cartridge casings
• International Forensic Automotive Paint Data Query (PDQ):-chemical/color information of original automotive paints • SICAR (shoeprint image capture and retrieval)• -shoeprint database
Forensic ScienceRichard Saferstein
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
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Forensic Pathology Forensic Pathology:
-investigation of unnatural/unexplained/violent deaths
-Cause and manner of death-autopsy -toxicology
Forensic ScienceRichard Saferstein
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
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Forensic Pathology After a human body expires there are several
stages of death. Rigor mortis results in the shortening of muscle tissue
and the stiffening of body parts in the position at death (occurs within the first 24 hrs. and disappears within 36 hrs.).
Livor mortis results in the settling of blood in areas of the body closest to the ground (begins immediately on death and continues up to 12 hrs.).
Algor mortis results in the loss of heat by a body (a general rule, beginning about an hour after death, the body loses heat by 1 to 1 1/2 degrees Fahrenheit per hour until the body reaches the environmental temperature).
Forensic ScienceRichard Saferstein
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.21
Beyond the Crime Scene
Beyond the crime scene to the autopsy room:
-medical examiner/coroner
-tissues/organs for pathological/toxicological examination
-secure items from the body for laboratory examination
Forensic ScienceRichard Saferstein
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.22
Beyond The Crime Scene
The following are to be collected and sent to the forensic laboratory:
1. Clothing2. Fingernail scrapings3. Head/pubic hairs4. Blood (DNA/toxicology) 5. Vaginal/anal/oral swabs (sex-related
crimes)6. Bullets from the body7. Hand swabs (Gunshot Residue)
Forensic ScienceRichard Saferstein
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.23
Forensic Anthropology Identification/examination of human skeletal
remains:-sex/approximate age/race/skeletal injury-create facial reconstructions to identify skeletal
remains
Sites of human remains treated as a crime scene-secured and thoroughly searched-locate all bones if scattered-footwear impressions-discarded items- aerial photography/metal detectors/ground-
penetrating radar/infrared photography/cadaver dogs
Forensic ScienceRichard Saferstein
© 2009 Pearson Education, Upper Saddle River, NJ 07458.
All Rights Reserved.24
Forensic Entomology Study of insects:
-estimate the time of death-postmortem interval (PMI)-different insect species used to estimate PMI-all entomological/insect collected -temperature readings-collect specimens from every area in which they
are found