Transcript The Crime Scene

• CSI mistakes
• CSI effect
Expert vs. Lay Witness
Functions of the Forensic Scientist
Forensic Scientists rely primarily on
scientific knowledge. However, only half
the job is performed in the laboratory
while the other half takes place in the
courtroom.
These functions fit into three categories:
1. Analyzing of Physical Evidence
 Physical evidence is less likely to be compromised
or tainted by human emotions than eyewitness
accounts from victims or witnesses
 the analysis of physical evidence involves
adherence to:
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strict guidelines
systematic collection
organization and analysis of information
OF INFORMATION (THE SCIENTIFIC METHOD)
 an understanding of admissibility of evidence is
important
 Frye, Daubert, Kumho, Coppolino
2. Providing Expert Testimony
• Forensic Scientist are called on to evaluate
evidence when the court lacks the expertise to
do so
• Must establish competency by citing
educational degrees, number of years of
occupational experience membership in
professional societies, special courses taken
and any professional articles or books
published.
• Cross-examination may reveal weaknesses in
background and knowledge
• Demeanor and ability to explain scientific data
clearly and logically to a judge and jury of nonscientists
• Must be an advocate of truth and not take a
side
3. Providing Training
 Evidence must be properly recognized, collected and
preserved if it is to have value.
 Many, but not all crime laboratories keep trained
“evidence technicians”.
 Sometimes a patrol officer or detective collects the
evidence.
 All officers engaged in fieldwork must be familiar with
evidence collection.
 These people are trained by laboratory staff through
extensive personal contact, lectures, laboratory tours
and/or dissemination of manuals.
Witnesses vs. Physical Evidence
• Most witnesses do not intentionally lie on the
witness stand
• Human observation is limited by memory,
suggestion, and interpretation
• Memories can be confused or altered, but
physical evidence stays the same
• bunny Effect video
• What is the first critical step of crime-scene
investigation? Why is this step so important?
• List a situation in which a warrantless search may
be justified.
– emergency circumstances
– prevent immediate loss or destruction of evidence
– search of a person and property within the immediate
control of the person provided it is made incident two
a lawful arrest
– consent by parties involved
JonBenet Questions
• What mistakes were made by the Boulder Police
Department in securing the crime scene?
• What specific kinds of evidence may have been
compromised?
• What could the police have done differently to
secure the crime scene and the evidence?
Bellringer:
Answer the following in your notes
• Police investigating an apparent suicide
collect the following items at the scene:
– a note purportedly written by the victim
– a revolver bearing very faint fingerprints
– traces of skin and blood from under the
victims fingernails
• What units of the crime laboratory will
examine each piece of evidence?
The Crime Scene
Forensic science begins at the crime scene;
It is imperative that physical evidence be recognized and properly
preserved.
Securing and Isolating
The first officer arriving at the scene must:
• preserve and protect as much as possible
• Priority given to those needing medical assistance and to
arresting the perpetrator.
• Once the scene has been secured, the lead investigator
determines the boundaries of the scene and establishes
the perpetrators path of entry and exit.
Securing Crime scene
• Properly secured and protected first
– thorough search to be sure there are no
suspects or physical danger
• safety PPE (personal protective equipment)
• Need to protect yourself: head, eyes, lungs,
hands, feet, and occasionally your entire
body
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Gloves
rubber booties for your feet
Goggles or a face shield
Respiratory filter to protect lungs
Recording the scene
• Notes, sketching and photography are used.
• These will aid the investigation and be presented at trials.
• It is becoming more common to use videotape as well.
Photography should include:
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photograph the shoes of everyone at the scene
Overview of surrounding area
Points of exit and entry
If indoors, each wall area should be shown
If there is a body, photos should show its position, injuries and
any weapons near by
The surface beneath the body
All items of physical evidence including close-ups
A ruler may be inserted near objects whose size may be of
significance.
Panoramic views can be produced by pasting together images.
 **If any items are moved, added or have changed position
photograph may not be admissible as evidence**.
Sketching
 Sketching is done after the photographs are
taken.
 A rough sketch is done first
 Objects are located by distance measurements
from two fixed points.
 Evidence is given letter designations
 A legend is included below the sketch
 A compass designating north is shown
 A finished sketch contains all of the information
in the rough sketch. It is drawn with
presentation in mind. Sometimes CAD is used
Rough Sketch
Finished Sketch
Notes
 Note taking is a constant activity throughout the processing of the
crime scene
 Notes should include:
 A detailed description of the scene
 The location of items of physical evidence recovered
 The time the physical evidence was discovered, by whom, how
and by whom it was packaged and marked.
 Other noteworthy sights, sounds, smells, etc.
 This record may be the only source of information for refreshing
one’s memory months, perhaps years, after a crime has been
processed.
Conducting a search
 Must be thorough and systematic
 Overlooked evidence can lead to accusations of a cover-up
attempt
 How one proceeds depends on the locale and size but must
include all probable points of entry and exit
 What to search for is determined by the type of crime, for
example in a homicide the focus will be on a search for the
weapon; a burglary: tool marks at the point of entry
 In most cases a search for latent fingerprints is required
 Careful vehicle searches are also done
Crime scene search patterns
Locard’s Exchange Principle
"Every Contact Leaves a Trace"
• The value of trace (or contact) forensic evidence
was first recognized by Edmund Locard in 1910.
• He was the director of the very first crime
laboratory in existence, located in Lyon, France.
The Locard’s Exchange Principle:
"with contact between two items, there will be an exchange."
For example, burglars will leave traces of their presence behind and
will also take traces with them. They may leave hairs from their body
or fibers from their clothing behind and they may take carpet fibers
away with them.
Source: http://www.virtualsciencefair.org/2004/fren4j0/public_html/trace_evidence.htm
Physical evidence
• How does the textbook define physical evidence?
– Physical evidence is any object that can establish
that a crime has been committed or can link a
crime and it's victim or a crime and it's
perpetrator.
• Forensic science starts at the crime scene where
evidence is recognized and properly preserved.
Steps in evidence collection
1.
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Photography (www.mycrimekit.com)
Sketches
Conduct a systematic search for evidence
Collect physical evidence
Maintain the chain of custody
Obtain standard reference samples
Submit evidence to the laboratory
Chain of Custody
• EVERY person who has come into contact with the
evidence
– handled
– examined
• Acts as a “paper trail”
• Failure to do so:
– lead to questions regarding the authenticity and
integrity of the evidence and the examinations
• When evidence is is analyzed there must be a new seal
made
Procedures for collecting evidence
• Procedures
– Identify the evidence
• (is it evidence, could it contain evidence?)
– Decide which type of packaging would be the most
appropriate
• (plastic pill bottle, manila envelope, paper bag, a
sealed container?)
– Record where evidence was found
• (living room, northeast corner of park, etc.)
– Label the evidence
• (victim’s shirt, hat)
– Date and intial
• (you will keep a record of when you collected the
evidence and that you collected)
• Tag the evidence for identification
• Seal the evidence
• (put tape on it to make sure no one else has
opened/compromised the sample)
• Fill out an evidence submission form
• Maintain records on chain of custody
• Every person that handles the evidence needs
to log it.
Types of physical evidence
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Paint
Glass
Explosives
Ballistics
Dust & Dirt
Impression evidence
Fracture matches
Wounds
• Questioned documents
• Insects
• DNA
Skeletal remains
• Body fluids
• Hairs & Fibers
Characteristics of evidence
• Class characteristics
features that place the
item into a specific
category
• Individual
characteristics
features that distinguish
one item from another
of the same type
Skeletal Remains
• Forensic anthropologists analyze skeletal remains to
determine four characteristics for a victim: age, sex, race,
and stature (height/build).
 Sex –examining the pelvis, humerus, and
femur
 Age and stature – analyzing the development
of the teeth, bone growth, and the length of specifc
bones, such as the femur.
 Race – analyzing the skull for characteristics
that are common among people of different races.
• DNA samples can be collected from bone, teeth, and
hair to provide clues to a person’s identity.
Scientists may also be able to gain clues as to a person’s
past, recent injuries, or the cause of death based on bone
fractures and other signs of trauma.
Source: http://www.crime-scene-investigator.net/excavation.html
Images: http://www.celticnz.org/images/Feedback/SkullSkeleton.JPG and http://www.legacyhealth.org/images/Housecalls/claviclefx.jpg
What do forensic anthropologists do?
Generally, forensic anthropologists DO NOT do any of the following:
• Collect trace evidence (hair, fibers)
• Run DNA tests
• Analyze ballistics or weapon evidence
• Analyze blood spatter
• Conduct autopsies
What a forensic anthropologist does DO to aid in a case:
• Goes to a crime scene to assist in the collection of human remains
• Cleans up the bones so that they may be looked at
• Analyzes skeletal remains to establish the profile of the individual
• Looks at trauma evident on the bones to establish the pathway of a bullet or the
number of stab wounds
• Works with a forensic odontologist (dentist) to match dental records
• Testifies in court about the identity of the individual and/or the injuries that
might be evident in the skeleton
Source: http://web.utk.edu/~fac/forensic.shtml
Body Fluids
• Blood, semen, saliva, sweat, and urine can be analyzed to give investigators information
about the crime as well as its victim or the suspect.
• Chemicals and ultra violet light
• find body fluid evidence
• Areas with potential evidence are swabbed, bagged and collected in vials, which
are air tight and have a low risk of cross contamination.
Examples:
 Vomit and urine can be used to test for alcohol,
drugs, and poisons.
 Cigarette butts may contain dried saliva.
 Semen containing sperm is valuable for DNA
analysis.
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Blood can provide DNA evidence and blood
spatter can provide clues about the crime.
Source: http://www.virtualsciencefair.org/2004/fren4j0/public_html/trace_evidence.htm
Images: http://www.trutv.com/library/crime/criminal_mind/forensics/chinatown_widow/4.html
Ù Conventional serology:
ò presence of blood in stains
ò species identification and
ABO grouping
ò is not adequately
informative to positive
identify a person
Ù DNA analysis can associate
victim and/or suspect with each
other or with the crime scene
Ù BLOODSTAIN PATTERNS
ò additional information
SEM: erythrocytes & lymphocytes
• BODY TISSUES
organ samples collected at
autopsy, including blood,
urine and stomach contents
• DRUGS & CONTROLLED
SUBSTANCES
toxicological analysis
volatile compounds (ethanol,
methanol, isopropanol)
heavy metals (arsenic)
nonvolatile organic compounds
(drugs of abuse, pharmaceuticals)
miscellaneous (strychnine,
cyanide)
trace drug presence, identity,
and quantity
plant materials, powders,
tablets, capsules
Black tar heroine wrapped in cellophane
• Wounds
• matched to weapons or tool marks on the
weapon.
• Investigators may also be able to
determine the weapon's size, shape, and
length.
• Analysis of a wound may provides clues:
• to a victim’s injuries
• characteristics of the suspect (left-handed,
right-handed, height, etc.)
• positions of the victim and suspect at the
time of the incident.
Image: (Bottom Left): http://dofs.gbi.georgia.gov/vgn/images/portal/cit_11783501/81672146questioned%20document.jpg
• DOCUMENTS
ransom note or other document to
find clues link it to a crime scene or
a specific suspect
analyze the type of paper used,
printing method or handwriting
style, and type of ink.
typed, handwritten and printed
materials for evidence of forgery
indented writings, obliterated or
altered writings, used carbon paper,
burned or charred paper
paper and ink analysis
handwriting comparison to
determine authenticity
Obliterated writing examination
Types of physical evidence
• SOILS & MINERALS
comparison between two or
more soils to determine if
they share a common origin
color, texture, composition
comparison
Layers of soil exposed at a grave site. Each
layer must be sampled
• WOOD
place the suspect at the
crime scene
side or end matching,
fracture matching and
species identification.
Cross-section - Xylem
Dust & Dirt
• Dust, dirt, or sand evidence can reveal where a
person has traveled and may be picked up at a
crime scene or left behind.
• Investigators examine the samples for chemical
composition, pollen, plant material, and other
organic matter to find links to a specific crime
scene.
Microscopic Image of Sand
Fingerprints
• There are 3 types of fingerprint patterns:
arches, loops, and whorls.
•Investigators
characteristics
also
identify
unique
ridge
• AFIS (Automated Fingerprint Identification
System) database used by investigators at local,
state, and national levels to search for matches to
fingerprints found at a crime scene.
Images: http://www.npsg.uwaterloo.ca/resources/images/microscope/Sand%200004.jpg
Types of physical evidence
• FINGERPRINTS
the strongest possible
evidence of a person’s
identity for explosives unless
there is DNA
Fingerprint Matching
• FIRE DEBRIS &
EXPLOSIVES RESIDUE
EXAMINATIONS
identification of accelerants
and explosive residues
Unburned accelerator liquid on a soot covered carpet
Explosives
•determine its chemical composition to identify the type of
explosive used and its origin.
• Traces of explosives found on a suspect’s clothing, skin, hair, or
other objects may be matched to explosives from the crime scene.
• Materials used to make an explosive device will be compared to
evidence found in the suspect’s possession to confirm a match.
Image: http://www.state.nj.us/njsp/divorg/invest/criminalistics.html
Ballistics
• Chemical tests can reveal gunshot residue (GSR) on:
• hands, face, or clothing of a victim or suspect
• indicate how close a person was to a fired gun.
• Rifling (grooves) in a gun barrel causes distinctive grooves, indentations and scratches
upon fired bullets, which can be matched to the weapon that fired them.
• Police are able to search the Integrated Ballistics Identification System (IBIS) database
to compare markings from bullets, cartridge cases, and shotgun shells to ballistic evidence.
Did you know?
Caliber (handguns & rifles) or gauge
(shotguns) refers to the size of the
internal diameter of a gun’s barrel.
Investigators can compare the
striations on bullets to see if
they match.
Image: http://www.geocities.com/j_ksinha/img/mid1.gif
• FIREARMS & AMMUNITION
individual microscopic marks
identification, source,
operability of firearms.
detection and characterization
of gunpowder residues
muzzle-to-garments distance
estimation
Photomicrograph: test
bullet - questioned bullet
GLASS FRAGMENTS
Cause of breakage
Direction of breakage force
Physical fitting
Glass fragment comparisons
determine its color, surface characteristics, tint, thickness, density, chemical
composition, and refractive index (RI).
Magnified image of glass fragments
The pattern of cracks in a windshield fracture
can reveal information about speed, occupant
position, and angle of impact.
Images: http://www.rsc.org/images/b606109e-300-(FOR-TRIDION)%20(iStockphotos)_tcm18-68354.jpg, http://www.mtcforensics.com/investigation.html
• HAIRS
hairs analysis can
determine
morphological features
DNA analysis
toxicological
examination
 FIBERS
human/animal
race
body area
cosmetic treatments
Microscopic Image
method of removal (crushed,
cut,
of
Hairs
&
burned, forcibly removed, fallenFibers
out naturally)
can associate a hair to a person
positive identification
presence of drugs and poisons
type (clothing, carpeting, furniture,
beds, and blankets)
color, composition construction
natural fibers from plants or animals or
synthetic fibers that are man-made.
Two matching hairs
identified with the
comparison microscope
Flax fibers viewed with
polarized light
Impression Evidence
Shoeprints & Tire Tracks
• photographed, lifted with tape, or cast with plaster
• Investigators will examine the evidence to identify:
• the brand of shoe or tire
• based on its tread pattern and other physical
features
• Shoes and tires will also show wear patterns
as well as other features (scratches, nicks,
and cuts)
Shoeprint
collected
using a
gelatin lifter.
Bite Marks
• Each of the 32 teeth in humans is unique due to age and wear.
• Impressions and photographs of bite marks left on a victim,
assailant, or other object at a crime scene
Tool Marks
• Tiny nicks and chips form on the edges of a tool as it is used
• Tools may also pick up traces:
• blood or other substances
• have fingerprints that can be lifted.
Images: http://www.wrongfulconvictionlawsuitdefense.com/uploads/image/28santos_600.jpg, http://www.dps.state.ia.us/DCI/Crime_Lab/images/toolmarks.jpg, &
http://www.masterpiecestudios.com/images/171463.gif
Paint
• Physical and chemical analysis of paint evidence (chips or residue) can indicate:
• class, such as automobile paint, house paint, nail polish, etc.
• compared to 40,000 different types of paint classified in a database
• Paint evidence can also indicate
• individual characteristics if an investigator is able to find similarities
between two samples, such as the color, number of layers, chemical
composition, or a physical match between the edges of two paint chips –
one from a tool and one from a crime scene.
Paint Transfer on a Car
Did you know?
Most paint evidence submitted to a lab will come
from hit-and-run cases involving automobiles.
Paint Layers
Physical Match of
Paint Chip Edges
Images: http://www.state.nj.us/njsp/divorg/invest/criminalistics.html
• PAINT & PAINT PRODUCTS
analysis and comparison of
paint transferred from the
surface of an object to another
during the commission of a
crime:
Suspect vehicle impacting a
victim vehicle; a pedestrian or a
stationary object
Tool impacting stationary object
Paint databases can help
identify the year, make and/or
color of a motor vehicle from a
chip of paint left at the scene.
Paint Layers on Wood Surface
Types of physical evidence
• TOOLMARK IDENTIFICATION
microscopic side-by-side
comparison
attempts to link a particular tool
with a particular mark to the
exclusion of any other tool
• ROPE & CORDAGE
composition, construction, color
and diameter
Spacing between teeth in gripping -major
role in toolmark examinations
manufacturer
Insects
• Flies, beetles, and other insects
can provide useful clues about a corpse.
• Forensic entomologists use factors to
estimate PMI (postmortem interval)
•weather conditions
•location
•condition of the body
•life cycles of insects
DNA
• Investigators can extract DNA from almost any tissue including:
• hair
• fingernails
• bones
• teeth
• body fluids
CODIS (Combined DNA Index System) is a database maintained by the
FBI that is used to find matches to unknown DNA samples from a crime
scene.
Images: http://biology.arizona.edu/sciconn/lessons2/Vuturo/vuturo/photos/desmus.gif