*
Unit 1
*4 elements of physical evidence:
*1) Recognition
*2) Classification
*3) Individualization
*4) Reconstruction
*First step is recognizing physical
objects as evidence or potential
evidence (called recognition)
*Experienced criminalists are trained
to recognize objects as evidence
*
*All evidence must be classified
*Classification is the process of putting objects
into groups with similar objects
*Can be confusing because classification can
mean individualization in some aspects (like
fingerprints), or it can mean identification (like
recognizing a small speck as a paint chip) in
other situations.
*
*Individualization
*Sometimes individualization
refers to:
*1) in some way, the
characteristics of
something make it
unique or one of a
kind among its class
members
*2) an object, when
compared to a known
item, has the same
origin
*
is narrowing down the
object from a class of
objects until only 1 item
remains in its class.
*Sometimes “partial
individualization” refers to a
case where the object is
narrowed down, but not to a
case of exclusivity. It
cannot be determined if it is
from the the source, nor can
it be ruled out.
* Exemplar- a known
specimen
* Evidentiary- a
specimen that is found
at the scene,
compared to an
exemplar
*
* Exclusion-opposite of
comparison, if at any
point there are differing
characteristics between
the evidentiary and
exemplar samples…it is an
absolute that they are not
from a common origin
* Problems with individualization:
* 1) There are not common
standards for how many
characteristics must match
before it is concluded that it
certainly came from a particular
source.
* Example: one investigator may
look at 6 hair samples and
another may look at 12 hair
samples to conclude that they
are from the same source.
* What can be individualized?
* Fingerprint evidence
* DNA evidence/Blood
evidence
* Toolmark impressions
* It can be useful;
* Use of physical
evidence analysis to
produce a theory of
the nature and
sequence of events
that must have created
the evidence
*
however, it is almost
entirely speculative in
nature.
* In addition, there is no
way to prove any of it
conclusively.
* https://www.youtube.
com/watch?v=YGaQd4u8dc
* 1) Change induced at the
scene, depositing something
at the scene or changing
something already there
* 2) Imprints or indentations,
such as footprints
* Imprint- object comes in
contact with a flat, hard
surface to make a 2
dimensional representation
of itself.
* Indentation- object is
impressed into a soft,
receiving surface (sand,
snow, mud) creating a 3-D
mark
* 3) Striations- hard surface
is marked by another
object in motion along its
surface
*
* 4) Damage- damage to physical
evidence can produce unique 2D
or 3D surfaces that can be used
in individualization
* 5) Exchange of material on
contact- called Locard Exchange
principle
* “When two objects come into
contact, there in an exchange of
material across the contact
boundary.”
*
* 6) Deposits- can be
made of large
quantities of materials
like blood or paint that
land in a particular
pattern, or even dust,
that leaves a void of
what was once there
*1) Formulate a working
hypothesis to determine
which physical evidence is
necessary to reconstructing
the event.
*
The evidence may support
the hypothesis or cause a
reevaluation of the
hypothesis if evidence
points to a contrary
scenario.
*
*2) Evidence is collected
that is deemed important
to the event or patterns
noted at the event.
*Remember, evidence of
exclusion is also very
important in finding a
suspect.
*
1) Provide Investigative
leads to develop MO (modus
operandi), or the
perpetrator’s method of
operation.
Databases also help provide
leads:
AFIS (fingerprints), CODIS
(DNA) and NIBIN (ballistics)
* AFIS makes fingerprints
extremely useful.
* Before AFIS, a person
would have to compare a
suspect fingerprints with
cards of 10 fingerprints.
* Due to time and energy
constraints, fingerprints
weren’t that useful until
the database was
developed.
*
* Can you think of any
other benefits to using
databases to search for
fingerprint and DNA
matches? Explain.
* 2) Establish linkages or
exclusions
* Linking physical
evidence with a
victim, perpetrator
and scene provide
compelling evidence.
* Multiple linkages can
strengthen several
weaker links.
*
* For example: a bakery is
robbed and a suspect is
stopped a few blocks away.
He claims he was never
near the place, but white
powder was found on his
clothes and was determined
to be flour. Since flour was
all over surfaces in the
bakery a linkage is present.
* A) A suspect in a burglary has
ceiling insulation on his
clothes and it was reported
the robber broke in through
the attic and ceiling.
* B) It is determined that a
hammer was used to murder a
person. A partial fingerprint
is found on the handle of the
hammer.
*
* C) A woman enters an
ER and claims she was
raped. During the
rape kit, they found
semen in her vaginal
tract and the DNA
indicates that someone
who lives her in
building is a match.
* 3) Physical evidence may
corroborate statements or
testimonies from witnesses
or victims.
* Sometimes evidence can be
useful even if it has no
ability to prove who
committed a crime.
Sometimes evidence just
enhances credibility.
*
* 4) Identification of Persons
, Substances or Materials
* Dental records, blood
droplets, fingerprints can
aid in identification of a
victim
* Substances must be tested
by trained scientists to
prove that they are a
controlled substance
* Often times forensic testing
must be done to confirm
that a crime has been
committed.
* Examples: powdered
substances collected are
indeed controlled
substance, fire debris
contains flammable liquid
residue
*
* All evidence is used to
determine corpus
delicti, which refers to
elements of a crime.
* Prosecutors must prove
the elements of a
crime “beyond a
reasonable doubt.”
* EVERY SCENE IS DIFFERENT!
Each scene must be
approached a little
differently. Considerations
must be made for location,
weather conditions, the
equipment and personnel
available and what type of
case it is.
*
* First and foremost is an
understanding of search
and seizure laws, which
vary from state to state.
* It is important that the
processor knows the
law…if evidence is
collected and violates
these laws, it is
inadmissable in court.
* The duty of first-responders
is to “render aid and
assistance” if applicable.
* If the suspect/perpetrator is
still on the scene then the
scene must be secured.
* Any injured persons may
need to receive assistance
from EMS.
*
* As soon as an emergency
situation is alleviated, the
scene must be secured and a
perimeter must be set up.
Depending on where the
scene is might help to
determine the perimeter.
* The purpose of the perimeter
is to keep unnecessary
people away from potential
physical evidence, even
extraneous police.
* Police on the scene
also obtain elimination
fingerprints and buccal
swabs of anyone who
enters the scene.
* Crime scene
investigators have this
data on file already.
*
* First responders also
get the names and
contact information
from any witnesses.
* Notes are taken about
relevant information in
the area…cars parked
nearby, etc.
* Step 1- Scene Survey and evidence recognition
* A “working hypothesis” is developed as to what
probably happened.
* The scene is surveyed to identify potential evidence
based on the working hypothesis.
* The working theory should be amended if evidence
is found that indicates a different scenario played
out at the scene.
* The theory is usually further refined as experiments
are done to replicate some types of evidence.
*
* 2) Conduct a scene search
* 4 methods:
* 1) Zone or quadrant search-
may be best for large or
outdoor areas
* 2) Strip search- can be used
anywhere, but is especially
effective in areas where there
is limited visibility (thick/shag
carpet, tall grass, etc.)
* 3) Contracting or expanding
spiral- works best if only one
investigator is at the scene
* 4) Double grid search
*
* 3) Documentation
* Notes, sketches, photographs
and video are all important
aspects of documenting the
scene.
* Video cannot replace all other
methods of documentation!
* Notes- MUST include things
that cannot be documented or
collected at the scene, but
even things that will be
documented or collected
should be in the notes
*
* Notes of first responders are
important because they are
closest to how the scene was
originally…
* Was door unlocked or locked?
Were there windows open?
* Even little details might be
important later.
* Logs to keep:
* 1) security- who entered and exited the scene
and when
* 2) photo – record of photos taken
* 3) evidence- what was collected
* A scene checklist is also helpful to ensure all
major tasks are completed before the scene is
released.
* Show exact location of buildings, permanent fixtures,
evidence, victim, etc. This is necessary because
photographs and video distort distances caused by
photographer/videographer perspective.
* 2 types:
* Rough (preliminary)- done at the scene, includes
measurements
* Smooth (finished)- done to scale, which is indicated on the
sketch
* Cross projection sketches are drawn based on the room as
a box that opens, so ceiling and wall info is also included.
* North is always indicated on any drawing.
*
*
* Technical aspects
* Virtually all photography now is done with
digital cameras.
* Lighting, sharpness and exposure are the key
technical elements in taking good photographs.
* Flash is usually best, except in situations where
you are photographing 3D impressions or
toolmarks. A slight amount of side lighting
provides shadow necessary for detail.
*
* Forensic aspects
* 1) Knowing what is important to photograph.
* 2) General guidelines
* Overall scene and subscenes from bigger to smaller.
(entrances and exits, room of scene)
* Evidence should be photographed in original location
before being collected. Then, markers or number plates
may be placed next to the evidence as well.
* Be sure to take photos of patterns that cannot be
collected. Tire marks, footprints should be taken parallel
to the plane.
* A ruler should be placed next to evidence to give scale.
*
* Useful as another way to document the scene, while
capturing the audible notes of CSI’s at the scene.
* Valuable for those not at the scene, other scientists
or police.
* Provides a back-up form of documentation.
* Can also be set up stationary to be used as a
security log.
* Overall, mid-range and close-up documentation rule
also applies to videography as well as photography.
*
* Generally, there is a duty to preserve evidence
and documentation for a long time.
* It may be years before the case comes to trial
and all of the appeals are dealt with. Most
states require evidence to be preserved at
least that long.
*
* 4) Evidence collection and preservation
* Bodies and their personal effects are the
responsibility of the medical examiner or
coroner.
* Detectives may attend autopsies to determine
time or manner of death (we will discuss
later).
* Medical examiners turn over physical evidence
from the body to the forensic science lab.
*
* The rule is to take evidentiary objects intact
whenever possible.
* If the object cannot be moved (floor, walls), a
sample must be removed from the item on which it
is located (substratam).
* Evidence collection techniques for trace evidence
include:
* Use of forceps
* Tape lifting
* Shaking
* Scraping
*
* Evidence is numbered.
The numbering method can
be decided upon by the department as long as its
consistent.
* The evidence must be labeled with this number and
it is also placed on the evidence log, along with a
brief description of the item.
* It is better to use adjectives that do not impart
identity or value if the collector is not sure of the
identity of the object.
* Example: “yellow metal ring” instead of gold ring;
“red brown stain” instead of bloodstain
*
* Items should be placed in a container proportional to
the size of the evidence.
* For powdered items, or specks of evidence, a druggist
fold is used to contain the evidence in a small piece of
rectangular paper.
* To complete a druggist fold:
* 1) fold the paper almost in half, a ½ inch difference.
2) fold the top over the shorter edge.3) repeat this
step but angle the fold. 4) fold the shorter edge in. 5)
after the evidence is placed in, fold the other end and
tuck the smaller end into the larger end.
*
* Plastic , ziptop bags are suitable for many types of
evidence EXCEPT evidence that is wet or soaked
with biological fluids.
* Wet or blood soaked evidence must be collected in
a paper evidence bag to prevent mold growth or
other degradation of evidence.
* Fire evidence must be in an airtight container to
trap any volatile liquids.
* Evidence is sealed at the scene with tamperproof
tape and signed or initialed across the tape by the
collector.
*
* It is important that the chain of custody be
maintained.
* This is the reason that there is an evidence log.
* When evidence is processed at the lab, the
evidence is packaged in a new container and
sealed and initialed by the lab tech.
*
* Investigators collect controls at the scene whenever
possible. 4 types:
* 1) Known (exemplar, reference)- known could be
buccal swab for DNA, known fibers from a carpet,
known paint sample, etc.
* 2) Alibi control- known but from a different source,
like from the place where the suspect says he
was…soil, paint, etc.
* 3) Blank control- specimen known to be free of the
item being tested, negative controls…
* 4) Substratum comparison- the underlying material or
surface on which the evidence has been found
*
* To effectively conduct a reconstruction, all the lab
reports concerning evidence must be completed and the
medical examiner’s report submitted (if relevant).
* A reconstruction is a “best theory”…note the use of the
term theory. Remember, theories have basis of
experimentation or evidence. They are NOT hypotheses!
* Many times experiments are conducted in the lab to
replicate evidence collected at the scene. Example:
blood stain patterns, distance determinations for
gunshot residue.
* Reenactments may be done by computer programs or
with actors and video cameras BUT are entirely
speculative! Just because the evidence may support the
reenactment DOES NOT mean it happened that way or in
the sequence presented!
*
* As the availability of computers, cell phones and
other devices have increased, so have the ability to
use these devices as evidence in crime in many
cases,
* The field of forensic computer science is increasing.
Some information is easily attained from
technological devices, but some information may
more difficult to find unless the investigator has
been trained in certain aspects of computer science.
*