Physical Evidence
Section 1A – Mastery Objectives & Critical Skills
1. Categorize the 18 common types of physical evidence as biological evidence, impression
evidence or manufactured evidence and give examples of each type
2. Explain the difference between identification and comparison of physical evidence
3. Describe the techniques used to identify each type of physical evidence
4. Discuss those types of evidence where comparison to a standard/reference is used
5. Explain why physical evidence is important and discuss its limitations in a criminal
investigation and prosecution.
6. Define class evidence and provide two factors that contribute to its weakness
7. List and summarize the forensic databases available
Section 1B –Vocabulary
Below is a list of all of the vocabulary terms used in this Unit. By the end of the Unit, you will be expected
to be able to write a working definition of each term and correctly use each term.
 class characteristics
individual characteristics AFIS
 comparison
product rule
NIBIN
identification
CODIS
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Section 2A –Required (!) and Suggested (*) Readings
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
!Safenstein, Richard and Fanning, Charles, (2011) “ForensicScience, an Introduction”pp84-96.
Section 2B –Relevant Websites / Videos for Reference
Refer to the class wiki (http://nnhsforensics.pbworks.com)
 Firearms Primer : http://www.videojug.com/interview/csi-and-firearms-2
Section 3 –In Class Activities
a) Lecture / slides
b) Analysis of a mock crime scene
c) Group project – types of physical evidence
Section 4 –– Outside Class Assignments
Thoughtfully answer each of the following questions. Include all your reasoning and show all your work. First,
copy and paste or retype the question with the correct number. In most cases your answer will consist of a series
of complete sentences unless otherwise indicated. No phrases, partial answers or isolated numbers will be given
credit.
Due dates for each assignment will be given in class and posted on the class wiki. (Please remember - homework
that is passed in late will be discounted 20%.
1. Positive identification of physical evidence must meet two criteria.
a. Describe these two criteria.
b. Explain why it is important to conduct tests that exclude all other substances.
2. When physical evidence is compared, two steps are followed.
a. Describe the first step for a particular category of physical evidence.
b. Describe the second step for the same physical evidence.
3. Statistics has a role in physical evidence.
a. What is the product rule and how does it relate to the concept of “individual
characteristics”?
b. Explain how the product rule can be used to determine whether two blood samples are
from the same source.
4. What is the difference between “individual characteristics” and “class characteristics”?
a. Describe a category of physical evidence where individual characteristics might be
impossible to determine.
b. Describe a category of physical evidence where individual characteristics are routinely
sought.
5. For each of the following, indicate whether the evidence is most likely to provide class or
individual characteristics:
a. An impression from a new automobile tire
b. A fingerprint
c. A spent bullet cartridge
d. A mass produced synthetic fiber
e. A portion of a shredded document
f. A sample of commercial potting soil
g. Skin and hair scrapings
h. Fragments of a multilayer custom automobile paint
6. Why is it important to have multiple pieces of class evidence from a crime scene when
individual evidence is not available?
7. In making the case to the jury, what is the value of class evidence?
8. Is there ever a situation in which too accurate a comparison hinders the usefulness of
physical evidence?
9. Fifty million fingerprints are cataloged in the AFIS database.
a. What does the abbreviation “AFIS” stand for?
b. Who maintains the database?
c. From where are the fingerprints obtained?
d. Describe the procedure for obtaining a “match” between your physical evidence and one
stored in AFIS
e. Does Interpol have a similar database?
10. Four million DNA samples are cataloged in the CODIS database.
a. What does the abbreviation “CODIS” stand for?
b. Who maintains the database?
c. From where are the DNA samples obtained?
d. Describe the procedure for obtaining a “match” between your physical evidence and one
stored in CODIS
e. Does Interpol have a similar database?
11. What is NIBIN and how is it used by the forensic scientists?
Section 5 –– Bonus Opportunities
1) Find a case study in which the physical evidence, was used to sentence a suspect and then
later was more carefully examined to free that same suspect. Select the pieces of physical
evidence that made the difference and explain how they were initially misrepresented and
then later used to exonerate the suspect.