UNIT 2: THE CRIME
SCENE
Collection, Protection and Analysis of Physical Evidence from the Crime Scene
UNIT 2: DAY 1
Do Now: What is the most important thing for the first
Police Officer to do when they enter a crime scene?
LEARNING OBJECTIVES
Today Students will:
 Define Physical Evidence
 Understand the responsibilities of the First Police Officer
to arrive at a crime scene
 Demonstrate the steps to be taken to thoroughly record the
crime scene
PHYSICAL EVIDENCE
 As automobiles run on gasoline, crime laboratories “run” on physical
evidence.
 Physical evidence encompasses any and all objects that can establish
that a crime has been committed or can provide a link between a crime
and its victim or a crime and its perpetrator.
 If physical evidence is to be used effectively for aiding the
investigator, its presence first must be recognized at the crime scene.
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THE BEGINNING: THE CRIME
SCENE
Forensic science begins at the crime scene.
The investigator must complete 2 essential
functions:
• recognize physical evidence
• properly preserve it for laboratory examination
The techniques of crime-scene investigation are
not difficult to master, it is expected that the
average police officer be able to perform them
properly.
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THE FIRST STEP: SECURE THE
SCENE
The first officer to arrive at the scene is responsible
for securing the crime scene.
• However, first priority is given to obtaining medical
assistance and/or to arresting the perpetrator.
As soon as possible, exclude all unauthorized
personnel from the scene.
Once the scene is secured, the preliminary exam must
begin.
• Recording the crime scene becomes a critical
piece to the investigation process.
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CRIME SCENE RECORDING
METHODS
Three methods for crime-scene recording
• Photography
• Sketching
• Note taking
Ideally all three should be employed at each crime scene
• Often personnel and monetary limitations may prohibit the
utilization of photography at every crime site.
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PHOTOGRAPHY OF A CRIME
SCENE
The crime scene must be in an unaltered condition.
Objects must not be moved until they have been
photographed from all necessary angles, (unless there are
injured parties involved).
As items of physical evidence are discovered, they are
photographed to show their position and location
relative to the entire scene.
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PHOTOGRAPHY
After the overviews are taken, close-ups
should be taken to record the details of the
object itself.
• When the size of an item is of
significance, a ruler or other measuring
scale may be inserted near the object
and included in the photograph as a
point of reference.
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PRACTICE PHOTOGRAPHING
A SCENE
 (15 min) In teams of 3-4
• Experiment with how your camera works, please be careful
• Use your camera to photograph your table, like a crime scene,
according to the notes just given
• Take at least five pictures which you think are relevant.
 (20 min)Share pictures and discuss their effectiveness in
documenting the scene.
UNIT 2: DAY 2
Do Now: What are two important things to be sure to do
when photographing a crime scene?
LEARNING OBJECTIVE
Today students will:
 Demonstrate the steps to be taken to thoroughly record the crime
scene
SKETCHES
Rough Sketch— A draft representation of all essential
information and measurements at a crime scene.
• This sketch is drawn at the crime scene.
• It shows all recovered items of physical evidence, as well as
other important features of the crime scene.
Finished Sketch— A precise rendering of the crime
scene, usually drawn to scale.
• This type is not normally completed at the crime scene.
• The finished sketch is drawn with care and concern
for aesthetic appearance.
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SKETCHING PRACTICE
 (8 min) Each person should do a rough sketch of everything on
the lab table.
 (3 min) Compare your sketches to those on your table.
• How are they different?
• Did anyone see anything you did not? Why?
• How can you be more accurate in the future?
WHY SKETCH?
Think (2 min), Pair (4 min) , Share(5min)
 What is the value of sketching?
 How does it compare, in importance, to photography?
 What additional value is added to the evidence by sketching?
 What are the essential characteristics of a sketch?
 How are rough sketches and finished sketches different?
NOTES
Note taking must be a constant activity throughout the
processing of the crime scene.
They must include a detailed written description of the
scene with the location of all items of physical evidence
recovered.
They must identify:
•
•
•
•
The time each piece of physical evidence was discovered
Who discovered it
How and by whom it was packaged and marked
What happened to the item after it was collected
This written record may be the only source of information
for refreshing one’s memory .
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PRACTICE NOTE TAKING
 (4 min) Complete a set of notes for this “Crime Scene”
 Be sure to include all relevant info.
RECORDING THE CRIME
SCENE
Investigators have only a limited amount of time to
work a crime site in its untouched state.
The opportunity to permanently record the scene in
its original state must not be lost.
Such records will not only prove useful during the
subsequent investigation but are also required for
presentation at a trial
• in order to document the condition of the crime site
and to delineate the location of physical evidence.
Every step of the investigation should be
documented thoroughly with an appropriate method.
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THE PRELIMINARY EXAM
A lead investigator will start the process of
evaluating the area.
• First, the boundaries of the scene must be determined.
• Followed by the establishment of the perpetrator’s path of entry
and exit.
• The investigator then proceeds with an initial walk-through of the
scene to gain an overview of the situation and develop a strategy
for the systematic examination and documentation of the entire
crime scene.
This is done before processing the crime scene for
physical evidence.
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UNIT 2: DAY 3
Do Now: What are the steps that must be taken to
thoroughly record the crime scene?
LEARNING OBJECTIVES
Today Students will:
 Describe proper procedures for conducting a systematic
search for physical evidence
 Describe proper procedures for packaging common types
of physical evidence
 Define and understand “chain of custody”
THE SEARCH OF THE CRIME
SCENE
The search for physical evidence must be thorough and
systematic.
The search pattern selected will normally depend on:
• the size and locale of the scene
• the number of collectors participating in the search.
For a factual, unbiased reconstruction of the crime, the
investigator—relying upon training and experience—must
not overlook any pertinent evidence.
Physical evidence can be anything from massive objects
to microscopic traces.
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THE SEARCH
Often, many items of evidence are clearly visible but
others may be detected only through examination at the
crime laboratory.
For this reason, it is important to collect possible carriers
of trace evidence, such as clothing, vacuum sweepings, and
fingernail scrapings, in addition to more discernible items.
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BEYOND THE CRIME SCENE
The following are to be collected and sent to the
forensic laboratory:
1. Victim’s clothing
2. Fingernail scrapings
3. Head and pubic hairs
4. Blood (for DNA typing purposes)
5. Vaginal, anal, and oral swabs (in sex related crimes)
6. Recovered bullets from the body
7. Hand swabs from shooting victims (for gunshot
residue analysis)
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BEYOND THE CRIME SCENE:
AUTOPSY
The search for physical evidence must extend beyond
the crime scene to the autopsy room of a deceased
victim.
• The medical examiner or coroner will carefully examine
the victim to establish a cause and manner of death.
(Why and How)
• Tissues and organs will be retained for pathological and
toxicological examination.
Arrangements must be made, between the examiner
and investigator to ensure that a variety of items that
may be obtainable from the body are secured.
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PACKAGING EVIDENCE
Each different item or similar items collected at different
locations must be placed in separate containers.
• Packaging evidence separately prevents damage through
contact and prevents cross-contamination.
The well-prepared evidence collector will arrive at a crime
scene with a large assortment of packaging materials and
tools ready to encounter any type of situation.
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PACKAGING TOOLS
Forceps and similar tools may have to be used to pick
up small items.
Unbreakable plastic pill bottles, with pressure lids, are
excellent containers for hairs, glass, fibers, and various
other kinds of small or trace evidence.
Alternatively, manila envelopes, screw-cap glass vials, or
cardboard pillboxes are adequate containers for most
trace evidence encountered at crime sites.
• Ordinary mailing envelopes should not be used as
evidence containers because powders and fine particles
will leak out of their corners.
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PACKAGING TOOLS
Small amounts of trace evidence can also be
conveniently packaged in a carefully folded paper,
using what is known as a “druggist fold.”
This type of packaging is called a Paper Bindle
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PRACTICE MAKING A PAPER
BINDLE
 Follow the directions on the hand out, carefully.
 When you have completed your first attempt, continue to practice
until you can do it without the directions.
 When you are ready, work with a partner to each make a paper
bindle and insert the provided trace evidence in it.
 Pass your bindle to your partner who will test it to see if any
evidence is being lost.
 When your bindle is approved by your partner, let me know by
posting a sticky note on your station.
UNIT 2: DAY 10
Do Now
•What kinds of packaging tools should an investigator bring
to the crime scene?
•What one thing was frequently missing from our crime scene
presentations?
LEARNING OBJECTIVE
Today Students will:
 Justify their decision about what type of search pattern should be used at
particular types of crime scenes
 Identify indicators of where to find important evidence to collect based
on the circumstances
 Recognize techniques for handling evidence
 Explain the importance of Chain of Custody
 Understand when to collect “Reference Samples”
THE SEARCH FOR EVIDENCE
 The investigator in charge assigns responsibility of searching a crime
scene.
 Whenever possible, 1 person should supervise evidence collection
• A forensic scientist is usually NOT involved, their work begins in the lab
• Some police agencies have trained field evidence collection technicians
who search for evidence
 The type of search pattern used depends on the location and size of
the area, as well as the actions of the suspect(s) and victim(s) at the scene.
 Proper control of the search is important, to minimize confusion and
ensure that no evidence is left behind
SEARCH PATTERNS
When attempting to locate evidence, detectives must be methodical.
One way to be certain they’ve combed every inch of a crime scene is to conduct
structured, patterned searches, such as spiral or grid searches.
Five Different Search Patterns
1.
2.
3.
4.
5.
Strip or Line Search
Grid Search
Spiral Search
Wheel/Ray Search
Quadrant or Zone Search
1.
STRIP OR LINE SEARCH
 One or two investigators start walking in a straight line,
perpendicular to the boundary edge
 They walk straight across to the opposite side boundary edge
 They then move further over on the boundary and walk back to
the original side
 They then repeat the walk back and forth until they cover the
entire search area
STRIP OR LINE SEARCH
• The space to be
searched is divided into
a series of lanes
• One or more searchers
proceed up and down
the lane, continuing
until the area has been
completely searched.
2.GRID SEARCH
 Consists of two strip searches, the
second perpendicular to the first
 Allows the area to be viewed
from two angles therefore is very
thorough.
 Must have well established
boundaries
 Good for large search areas
3. SPIRAL SEARCH
• Typically used outdoors
• Normally launched by a single
person who begins at the outermost
corner and walks in a decreasing
spiral toward a central point.
• Inward is helpful because the
investigator moves from an are light
with evidence to an area with more
• Can also be conducted from the
center out
• A perfect spiral is difficult to do
4. WHEEL/RAY SEARCH
• A search pattern in which the
area is divided into pie-shaped
sections, usually six in number.
• Several people move from the
boundary straight toward the
center
• This is not the preferred
method because the area
between the rays is not well
searched
5. QUADRANT OR ZONE
SEARCH
• The area is divided into
quadrants, each of which is
then examined with one of
the other patterns.
• Team members are
assigned to search specific
quadrants
• Search must include all
probable points of entry
and exit
• Well suited for large search
areas
LOCATING PHYSICAL
EVIDENCE
The investigators skill in recognizing evidence is very
important in effective crime scene processing
Experience plays a major role in helping investigators develop
a successful strategy for recovering relevant physical evidence
The circumstances of the crime help detectives know what to
look for
PHYSICAL EVIDENCE IN
DIFFERENT CIRCUMSTANCES
Homicides: search centers on the weapon and
cross-transfer evidence between the victim and the
perpetrator, (hairs, blood, and fibers)
Burglaries: search focuses on points of entry and
tool marks
A careful search for latent fingerprints is required at
most crime scenes
PHYSICAL EVIDENCE IN
DIFFERENT CIRCUMSTANCES
Vehicle Searches: Must be carefully planned and
systematically executed
• The amount of detail paid in the search depends on
the nature of the case
• Hit and Run: careful search of outside and undercarriage is
important. (evidence from cross0transfer between car and
victim (blood, tissue, hair, fibers, fabric impressions, paint
traces or glass fragments)
• Homicide, Burglary, Kidnapping: all areas both inside and
out are searched thoroughly
COLLECTING PHYSICAL
EVIDENCE
 Some evidence is obvious, other evidence can only be detected in the lab
• Trace blood evidence, hairs and fibers may only be revealed through vacuum
sweeping or on clothes only after close scrutiny in the lab
 It is essential to collect all possible carriers of trace evidence
• Often all clothing worn by crime participants is collected
• Each clothing item should be wrapped separately
 Critical areas should be vacuumed and sweepings should be sent to the lab
• Sweepings from different areas should be packaged separately
 Fingernail scrapings should be collected from anyone who was in contact
with others
• Scrape undersurface with a dull object, like toothpick (do not cut skin)- to lab
HANDLING EVIDENCE
 Handled in a way that leaves evidence unchanged between the scene and the lab
• Avoid contamination, breakage, evaporation, scratching or bending which can occur
as a result of poor packaging or careless handling
 Use latex gloves and/or forceps when touching evidence
• Be sure to sanitize tools between each piece of evidence
 Investigators should not remove blood, hairs, fibers, soil particles, or anything
else from clothes, weapons or other articles
• Send the entire object to the lab
 Use common sense when dealing with evidence on a large structure (door, wall,
or floor) remove it with appropriate tool
HANDLING BLOOD
EVIDENCE
Bloodstains, options
• Scrape stain off the surface
• Transfer the stain to a moistened swab
• Cut out the area of the object bearing the stain
Which to do must be decided by the investigators on
scene
PACKAGING
Although pill bottles, vials, pillboxes, or manila
envelopes are good universal containers for most
trace evidence, one frequent find at crime scenes
warrants special attention.
• bloodstained materials (collect with disposable tools)
• if stored in airtight containers, the accumulation of
moisture may encourage the growth of mold, which
can destroy the evidential value of blood.
• In these instances, wrapping paper, manila envelopes,
or paper bags are recommended packaging materials
DNA EVIDENCE
 Can be found in really tiny samples on evidence which has come into contact with
sweat, saliva or skin cells
 Search should include all objects which the suspect or victim may have come into
bodily contact with
 Likely sources
• Stamps and envelopes
• Cup or can
• Gum, sweatband of a hat or bed sheet
 Collect wearing a face mask , as well as disposable gloves and forceps, (sometimes
coveralls and shoe covers are also worn)
CHAIN OF CUSTODY
Chain of Custody—A list of all persons who came into
possession of an item of evidence.
Continuity of possession, or the chain of custody,
must be established whenever evidence is presented in
court as an exhibit.
Adherence to standard procedures in recording the
location of evidence, marking it for identification, and
properly completing evidence submission forms for
laboratory analysis is critical to chain of custody.
• This means that every person who handled or
examined the evidence and where it is at all times
must be accounted for.
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CHAIN OF CUSTODY
 Fill out preprinted id forms or attach an evidence tag to every
container
 Investigator initials as well as the date must be written on the evidence
seal tape
 Every person who possesses the evidence must maintain a written
record of its acquisition and disposition
 Often all people involved in the collection and transport of evidence
must testify in court; minimize those in contact with it
OBTAINING REFERENCE
SAMPLES
Standard/Reference Sample—Physical evidence whose
origin is known, such as blood or hair from a suspect, that can be
compared to crime-scene evidence.
The examination of evidence, whether it is soil,
blood, glass, hair, fibers, and so on, often requires
comparison with a known standard/reference sample.
Although most investigators have little difficulty
recognizing and collecting relevant crime-scene
evidence, few seem aware of the necessity and
importance of providing the crime lab with a thorough
sampling of standard/reference materials.
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APPLY YOUR KNOWLEDGE
Each Investigative team will be given a scenario, it is your job to answer all of the
following questions about how you would find and collect the physical evidence.
Be prepared to report out, write your answers and justifications on a chart paper:
1. What search method should you use?
2. What type of evidence should you especially be looking for and where should
you look? Why?
3. What special handling and packaging considerations will you have to address?
Why?
4. Should you collect reference samples? If so, from whom or where?
SCENARIOS
1. At a public park, there was a hit and run accident, car vs pedestrian.
2. Carjacking and abandonment in alley
3. Burglary and assault in Cumberland Farms store
4.
Jewelry store robbery, when closed
5. Homicide in car and on pavement in the mall parking garage
6. Burglary at a private home when owners were on vacation
UNIT 2: DAY 11
Do Now: Why are the procedures for collecting, packaging
and transporting physical evidence important?
LEARNING OBJECTIVES
Today Students will:
 Demonstrate ability to select proper search techniques.
 Demonstrate understanding of procedures which will
maintain health and safety standards at the crime scene
 Understand the implications of the “Mincey” and “Tyler”
Cases
PREPARE TO REPORT OUT
15 min
 Chart your answers
 Prepare to explain choices
REPORT CHOICES
20-25 min
 Each group has 3-4 minutes
CRIME SCENE SAFETY
The increasing spread of AIDS and hepatitis B has
sensitized the law enforcement community to the
potential health hazards that can exist at crime scenes.
• In reality, law enforcement officers have an
extremely small chance of contracting AIDS or
hepatitis at the crime scene.
The International Association for Identification
Safety Committee has proposed guidelines to protect
investigators at crime scenes containing potentially
infectious materials that should be adhered to at all
times.
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GUIDELINES TO PROTECT
INVESTIGATORS
1. Double glove and shoe covers, sometimes liquid repellant coveralls
2. Particle mask/respirator, goggles or face shield : when potentially infectious
dust or mist may be encountered (scraping collection)
3. Be alert to sharps and properly package, use special fingerprint brush
which can be decontaminated
4. Biohazard red bag for glove, clothing, mask, etc disposal
GUIDELINES TO PROTECT
INVESTIGATORS
5. Note taking should be done with clean gloves. Pens used to mark
contaminated evidence should be biohazard disposed
6. Remove soiled or torn protective equipment immediately then
decontaminate affected areas
7. Food, drink, makeup application and smoking are prohibited at crime
scene with biological evidence
8. Infectious linen bag (yellow) for non disposable items, washed by
specialized laundry service, through the department –NEVER TAKE IT
HOME
LEGAL CONSIDERATIONS
Pg 46-bottom
In pairs; read the given section and answer the following questions.
 What is unreasonable search and seizure?
 What are 4th amendment privileges?
 What circumstances allow for a police search, without a warrant,
according to the supreme court?
THE MINCEY AND TYLER
CASES
 What Important Findings came out of each of these cases?
 In your groups, you will read the synthesis of the assigned case
and explain the implications of the ruling and explain how it relates to
the legal considerations of evidence collection.
• Post your answers on chart paper for report out
UNIT 2: DAY 12
Do Now: What procedures are required to maintain health
and safety standards at the crime scene?
LEARNING OBJECTIVES
Today Students will:
 Demonstrate the process of Securing, Isolating and Recording
a crime scene
 Explain the Forensic challenges in “ The Enrique Camarena
Case”
 Demonstrate understanding of Crime Scene Processing and
Evidence Documentation
QUIZ: THE CRIME SCENE
CASE STUDY: ENRIQUE
CAMARENA CASE (50 MIN)
 Explain the Forensic challenges in “ The Enrique Camarena Case”
 Work in your groups to address the case study questions.
 Be prepared to report out
UNIT 2: DAY
Do Now: What types of physical evidence may be collected at
the crime scene?
LEARNING OBJECTIVES (5)
Today Students will:
 Review common types of evidence
 Understand the significance and value of physical evidence
 Compare and contrast identification and comparison of
physical evidence
PHYSICAL EVIDENCE
It is impossible to list all the objects that could
conceivably be of importance to a crime.
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 that will be decided by a jury.
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
1.
Blood, semen, and saliva: in a form suggesting a relationship to the crime or the people involved
• Set out for serological and biochemical analysis
2.
3.
4.
Documents: submitted for authenticity or to determine source
Drugs: in violation of laws regulating sale, distribution, use or manufacturing
Explosives: objects containing residue of a discharged explosive or containing and explosive
charge
5. Fibers: natural or synthetic; able to establish a relationship between objects and people
6. Fingerprints: latent and visible
7. Firearms and ammunition: all firearms and ammunition, discharged or intact, suspected to be
involved in a criminal case
8. Glass: particle or fragment that may have been transferred during a criminal act ( including
windows with holes)
9. Hair: animal or human which could link a person to a crime
10. Impressions: Tire marks, shoe prints, depressions in soil, glove or fabric impressions, bite-marks
on food or skin
11. Organs and physiological fluids: submitted for toxicology, looking for drugs or poisons (blood
included)
TYPES OF PHYSICAL
EVIDENCE
12. Paint: transferred during a crime, dry or wet
13. Petroleum products: gas residue removed from arson scene, grease or oil stains whose presence
suggests involvement in a crime
14. Plastic bags: particularly in homicide or drug investigations, links suspect to similar bag in their
possession ( reference sample)
15. Plastic, rubber, and other polymers: pieces of these manufactured materials may be linked to objects
in possession of suspect
16. Powder residues: items suspected to contain evidence of a discharged firearm
17. Soil and minerals: could link a person or object to a location
18. Tool marks: objects suspected to contain impressions of another object suspected used in a crime
19. Vehicle lights: headlights and tail lights examined to determine if it was on or off at time of impact
20. Wood and other vegetative matter: wood sawdust, shavings, plant material on shoes or tools which
may be used to link crime to person or object.
SIGNIFICANCE
 For Identification or For Comparison
Identification to determination the physical or chemical identity of a substance
with as near absolute certainty as existing analytical techniques will permit.
A 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 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
The crime laboratory is frequently requested to
identify the chemical composition of an illicit drug.
It may be asked to identify gasoline in residues
recovered from the debris of a fire, or it may have to
identify the nature of explosive residues—for
example, dynamite or TNT.
The identification of blood, semen, hair, or wood
are also very common and as a matter of routine,
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.
Both the standard/reference and the suspect specimen
are subject to the same tests.
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.
ROLE OF PROBABILITY
To comprehend the evidential value of a comparison,
one must appreciate the role that probability has in
ascertaining the origins of two or more specimens.
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.
Class Characteristics
• Evidence associated only with a group is said to have
class characteristics.
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.
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
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.
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.
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.
CLASS EVIDENCE
The chances are low 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 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.
UNIT 2:
Do Now: What is the difference between comparison and
identification of physical evidence?
Homework: Prepare for unit test on Friday!
LEARNING OBJECTIVES (6)
Today Students will:
 Explain the differences between types of evidence and the
importance of probability in their use
 Understand the significance of natural variations
TURN AND TALK (9 MIN)
 Provide three examples of evidence collected which would most likely have individual
characteristics
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What types of evidence?
How could it be used?
Why do you think this is true?
Is probability important? explain
 Provide three examples of evidence collected which would most likely have class
characteristics
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What types of evidence?
How could it be used?
Why do you think this is true?
Is probability important? explain
SHARE FINDINGS( 14 MIN)
 3 individual characteristic
 3 class characteristic
 Are there certain types of evidence which usually fall into one of these
categories? Why or why not?
 Is one of these types more valuable than the other? Explain
 What role does probability play?
 How does this compare with common understanding of evidence value as
portrayed on TV?
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
USING PHYSICAL EVIDENCE
 As the number of different objects linking an individual to a crime
scene increases, so does the likelihood of that individual’s
involvement with the crime.
 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.
EXIT TICKET(7 MIN)
1.
What are 5 common types of evidence
2.
How is physical evidence significant?
3.
Is all physical evidence of equal value? Explain as it relates to
probability
4.
Compare and contrast identification and comparison of physical
evidence
5.
How are class and individual classifications different?
6.
What is natural variation and why is it important?
UNIT 2: MARCH 20
Do Now: What is the difference between natural limits and
evidential limits?
HOMEWORK: Read the case study
LEARNING OBJECTIVES (7)
Today Students will:
 List and explain the function of Forensic Databases
 Explain the importance of Forensic Pathologists,
Anthropologists and Entomologists
DATABASES
 A database is an organized list of facts and information.
 Databases usually contain text and numbers, and frequently hold still
images, sounds and video or film clips.
 Government and private forensic databases can help both law enforcement
investigators and the scientists who support their work in the lab.
 They allow the crime lab to link evidence to suspects or crimes committed
using the same tool or pattern.
 They make the crime lab a more active component of the investigation by
allowing them to access people and cases in all 50 states and around the world.
DATA BASES
 The Integrated Automated Fingerprint Identification System (IAFIS), a
national fingerprint and criminal history system maintained by the FBI.
 The Combined DNA Index System (CODIS) enables federal, state, and local
crime laboratories to electronically exchange and compare DNA profiles.
 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.
 The International Forensic Automotive Paint Data Query (PDQ) database
contains chemical and color information pertaining to original automotive paints.
 SICAR (shoeprint image capture and retrieval) is a shoeprint database.
JIGSAW(20MIN)
Explain the role of Pathologist, Anthropologist, Entomologists in
evidence collection
 What kinds of samples do they collect? Be as specific as possible
 How does it inform investigators?
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What can they tell us about the victim, perpetrator, crime details?
How accurate are their findings? Probabilities?
Is it usually class or individual?
Are there clear standards used to identify natural variations?
 Why are they important?
REPORT OUT
UNIT 2:MARCH 21
Do Now: What type of evidence was most important in the
Wayne Williams Case?
Homework: Complete chapter 3 review and
study for the unit test which is tomorrow!
LEARNING OBJECTIVES
Today Students Will:
 Review the roles of the Forensic Pathologists, Anthropologists
and Entomologists
 Evaluate the role of fiber evidence in presenting a case at trial
 Perform a Case Study Analysis
 Present findings from a case study of “ the Wayne Williams
Trial”
FORENSIC PATHOLOGY
What is it?
 This field involves the investigation of sudden, unnatural,
unexplained, or violent deaths.
What do they do?
 The primary role of the medical examiner is to determine the cause
of death.
 If a cause cannot be found through observation, an autopsy is
normally performed to establish the cause of death.
FORENSIC PATHOLOGY
How do they do that?
There are several stages of death, these stages are used to establish time 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 hours and disappears within 36 hours).
 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 hours). It can also be used to determine if a body has
been moved, (No settling where contacted with surface).
 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
ANTHROPOLOGY
What is it?
 Forensic anthropology is concerned primarily with the identification and examination of
human skeletal remains.
What do they do?
 Because of their resistance to rapid decomposition, skeletal remains can provide a multitude
of individual characteristics such as sex, approximate age, race, and skeletal injury.
How do they do it?
 The gender of the decedent can be determined by the size and shape of various skeletal
features, especially those in the pelvis and skull or cranium.
 The height of the victim when alive can be estimated by measuring the long bones of the
skeleton especially in the lower limbs.
FORENSIC ENTOMOLOGY
What is it?
 The study of insects and their relation to a criminal investigation is known as forensic entomology.
What do they do?
 They estimate the time of death when the circumstances surrounding the crime are unknown.
How do they do it?
 This determination can be carried out by studying the stage of development of maggots or insect
sequence of arrival.
 After decomposition begins, insects that feed on the dead tissue infest the body and lay eggs, usually
within 24 hours.
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The most common and important of these is the blowfly recognized by its green or blue coloration.
 Forensic entomologists can approximate how long a body has been left exposed by examining
the stage of development of the fly larvae.
CASE STUDY ANALYSIS
 Analyze the evidence and explain the forensic case in the Wayne
Williams Trial
 Work in assigned pairs to address the case study questions.
 Be prepared to report out
REPORT OUT
 How was the use of fiber evidence unique, in this case?
 What two fibers were of particular importance?
 How did investigators gather the evidence provided by the fibers?
 What did this evidence tell them, and how did they use it to locate the perpetrator?
 What role did reference samples play in this case?
 How were the samples compared? Be specific
 How was the concept of probability used in this case?
 Why do you think the suspect was only charged with 2 murders?
UNIT 2: MARCH 22
Do Now: Review Unit Concepts
LEARNING OBJECTIVES
Today Students Will:
 Demonstrate understanding of unit concepts on unit
assessment
JEOPARDY TIME!(20 MIN)
 Compete with your classmates to earn bonus points on the unit
test
CRIME SCENE UNIT TEST
 Read the questions carefully and do your best!