Download The Crime Scene - Miami Beach Senior High School

The Crime Scene
Chapter 2
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
• Valuable only when its collection is
performed correctly
Physical Evidence
• Crime labs DO NOT solve crimes– they just
analyze the evidence
– Investigators solve crimes
Crime Scenes
• It is the beginning point for obtaining
evidence which will be used by the crime
scene investigator and the forensic expert
• A thorough investigation of the crime scene
must be completed
Defining a Crime Scene
• Crime scenes are never consistent- they are
ALWAYS inconsistent
– Each one presents an investigator with a new
challenge
• Can be classified by the location of the
crime
– Primary crime scene
– Secondary crime scene
Defining a Crime Scene
• Crime scenes may also be classified
according to size
– Macroscopic
• Comprised of many crime scenes
• Gunshot an victim’s body dumped in field
– Microscopic
• Trace evidence found on the body, gunshot residue,
or tire tread marks
Defining a Crime Scene
• Also classified by
– Type of crime
• Homicide, robbery, burglary, sexual assault
– By organization or disorganization of scene
– Physical location
• Indoor, outside, vehicle
– Criminal behavior associated with scene
• Passive or active
Crime Scene Investigation
• Based on the scientific method and the
Locard Exchange Principle, logic and
forensic techniques involve
– Recognition- scene survey, documentation,
collection
– Identification- comparison testing
– Individualization- evaluation and interpretation
– Reconstruction- reporting and presenting
Crime Scene Investigation
• Goals are to determine the following
–
–
–
–
–
–
What happened
Where did it happen
When did it happen
Why did it happen
Who may have perpetrated these actions
How was the incident carried out
Processing a Crime Scene
• 8 universal rules exist
–
–
–
–
–
–
–
–
Safety first
Secure and protect the scene
Fulfill the basic legal requirements
Photograph the scene
Identify and mark evidence
Collect, label, and package evidence
Diagram the scene
Write a report
The Crime Scene
• The first officer at the crime scene is responsible
for securing and protecting the area
– Must first make sure that if the victim is alive, medics
are on their way
– Must secure the area with crime scene tape or other
barriers
– Must make sure that the evidence does not get
compromised
– Must make sure that witnesses do not leave the crime
scene
First Responders must protect the
scene
• Every individual who enters the scene has
the potential to destroy physical evidence,
even if by unintentional carelessness. To
exercise proper control over the crime
scene, the officer protecting it must have the
authority to exclude everyone, including
fellow police officers not directly involved
in processing the site or in conducting the
investigation.
The Crime Scene Investigator
• Has only a limited amount of time to work a
crime scene
–
–
–
–
Must photograph the crime scene
Must sketch the crime scene
Must take notes
Must collect, document, and package evidence
Photography
• The crime scene must not be altered
– Objects must remain where they are until
photographed
– Any proof that the crime scene was
compromised would cause the evidence to not
be admissible in court
– If evidence has been removed or moved, it must
be mentioned in the report
Photography
• Each crime scene needs to be photographed as
completely as possible
• All areas where the crime took place should be
photographed at different angles
• Entries and exits must also be photographed at
different angles
• It is important to have close-up shots and far-away
shots
• Evidence should be photographed with a ruler as a
point of reference
Sketches
• After photographs are taken, the investigator will
sketch the crime scene
• 2 types of sketches exist
– Rough- a draft representation of all essential info and
measurements at a crime scene
– Finished- a precise rendering of the crime scene
• All sketches are drawn to scale
• All sketches have a legend showing where certain
items are at the crime scene
Sketches
• Crime scene sketches require
–
–
–
–
–
–
–
Title or caption
Legend of abbreviations
Symbols
Numbers of letters used
Compass designation
Scale, if drawn to scale
Documentation block with case number, offense type,
victim’s names, location, date and time, and sketcher’s
name
Notes
• Must be taken throughout processing the
crime
• Should include
– Date and time of notification and information
received
– Arrival information
– Scene description
– Victim description
– Crime scene team members
Notes
• Must also include a detailed written
description of the scene with the location of
items of physical evidence recovered
– Must also identify the time an evidence was
discovered, by whom, how and by whom it was
packaged and marked, and the disposition of
the item after it was collected
Infuential factors
• How one conducts a crimescene search will
depend on the 1. locale and 2. size of the
area, as well as on the 3. actions of the
suspect(s) and victim(s) at the scene
Search for Evidence
• Must be thorough and systematic
– Must make sure not to overlook any pertinent
evidence
– Failure to do so can lead to accusations of
negligence or of covering up the evidence
Search for Evidence
• Field evidence technician responsible for
conducting search for evidence
– May also photograph the crime scene
– Looks for fingerprints, footprints, tool marks,
hairs, fibers, etc
– Must also collect possible carriers of trace
evidence
Search for Evidence
• Crime scene is usually searched in segments
– 4 types of segments exist
• Spiral search method- Search starts at an outer point
and gradually moves toward the center
• Grid method- Crime scene divided into a grid and
each grid segment is searched
• Strip or line search- Crime scene divided into strips
and each strip is searched
• Quadrant or zone search- Crime scene divided into
quadrants and each quadrant is searched
Search for Evidence
• Evidence must also be collected from the body (if
victim died) by the medical examiner
– Evidence needed includes
•
•
•
•
•
•
•
Victim’s clothing
Fingernail scrapings
Head and pubic hairs
Blood
Vaginal, anal, and oral swabs (sex crimes)
Recovered bullets from the body
Hand swabs from shooting victims
Collecting and Packaging Evidence
• Physical evidence must be handled and
processed in a way that prevents any change
from taking place between the time it is
removed from the crime scene and the time
it is received by the crime laboratory
Integrity
• The integrity of evidence is best maintained
when the item is kept in its original
condition as found at the crime site.
Whenever possible, evidence should be
submitted to the laboratory intact. Blood,
hairs, fibers, soil particles, and other types
of trace evidence should not normally be
removed from garments, weapons, or other
articles that bear them. Instead, the entire
object should be sent to the laboratory for
processing.
Collecting and Packaging Evidence
• Each different item or similar items
collected at different locations must be
placed in separate containers
– Prevents damage through contact and prevents
cross- contamination
• Forceps and other similar tools may have to
be used to pick up small items
Collecting and Packaging Evidence
• Small items may be put in unbreakable plastic pill
bottles with pressure lids
– Great for hairs, glass, fibers, and other small or trace
evidence
• Manila envelopes are also good containers for
evidence
• Paper bags are excellent containers for large
evidence
• Mailing envelopes should NEVER be used to hold
evidence
Collecting and Packaging Evidence
• Any evidence that is wet must be air dried
before being placed in a container
• Bloodstained evidence should never be
stored in an air-tight container
– Could cause mold growth which damages the
evidence
Collecting and Packaging Evidence
• After evidence is collected and packaged,
the container it is in must be marked and
sealed
• Most items should be packaged in a primary
container and then placed in a secondary
container
– Hair is placed in a vial which is then placed
inside a paper bag
Druggist Fold
• Small amounts of trace evidence can also
be conveniently packaged in a carefully
folded paper, using what is known as a
“druggist fold.” This consists of folding
one end of the paper over one-third, then
folding the other end (one-third) over
that, and repeating the process from the
other two sides. After the paper is folded
in this manner, the outside two edges are
tucked into each other to produce a
closed container that keeps the specimen
from falling out.
Chain of Custody
• Is a list of all persons who come in possession of
an item of evidence
• Must be established whenever evidence is
presented in court
– The evidence container must be marked for
identification
– The collector’s initials should be placed on the seal
– If evidence is turned over to another person, the transfer
must be recorded
Obtaining Reference Samples
• A standard/reference point is physical
evidence whose origin is known, such as
hair from a suspect that can be compared to
a hair found at the crime scene
– Exists with blood, glass, soil, fibers, paint
chips, etc
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.
Obtaining Reference Samples
• 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.
Substrate Controls
• These are materials close to areas where
physical evidence has been deposited. For
example, substrate controls are normally
collected at arson scenes. If an investigator
suspects that a particular surface has been
exposed to gasoline or some other
accelerant, the investigator should also
collect a piece of the same surface material
that is believed not to have been exposed to
the accelerant.
Substrate controls example
• Another common example of a substrate
control is a material on which a bloodstain
has been deposited. Unstained areas close to
the stain may be sampled to determine
whether this material can interfere with the
interpretation of laboratory results.
Thorough collection and proper packaging
of standard/reference specimens and
substrate controls are the mark of a skilled
investigator.
Special Forensic Science Services
• Forensic Pathology involves the investigation of
unnatural, unexplained, or violent deaths.
– Forensic pathologists in their role as medical
examiners or coroners are charged with
determining cause of death.
Special Forensic Science Services
– The forensic pathologist may conduct an
autopsy which is the medical dissection and
examination of a body in order to determine the
cause of death. Autopsies are generally
performed if the death is deemed suspicious.
Special Forensic Science Services
• 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.).
Special Forensic Science Services
– 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).
Special Forensic Science Services
• Forensic Anthropology is concerned primarily
with the identification and examination of human
skeletal remains. Identification is done by
examining bones that may identify race or sex or
injury or they may create a facial reconstruction
Courtesy of C. Fanning
Special Forensic Science Services
• Forensic Entomology is the study of insects and
their relation to a criminal investigation,
commonly used to estimate the time of death.
Forensic Entomology
• These determinations are not always
straightforward, however. The time required for
stage development is affected by environmental
influences such as geographical location, climate,
and weather conditions. For example, cold
temperatures hinder the development of fly eggs
into adult flies. The forensic entomologist must
consider these conditions when estimating the
postmortem interval. Knowledge of insects, their
life cycles, and their habits make entomological
evidence an invaluable tool for an investigation