Forensic Science
T. Trimpe 2006 http://sciencespot.net
Crime Scene Vocabulary
CRIME SCENE: Any physical location in which a crime has occurred or is
suspected of having occurred.
PRIMARY CRIME SCENE: The original location of a crime or
accident.
SECONDARY CRIME SCENE: An alternate location where
additional evidence may be found.
SUSPECT: Person thought to be capable of committing a crime.
ACCOMPLICE: Person associated with someone suspected of committing a crime.
ALIBI: Statement of where a suspect was at the time of a crime.
Source: http://www3.sc.maricopa.edu/ajs/crime_scene_technician.htm
Types of Evidence
Testimonial evidence includes oral or written statements given to police as well as
court testimony by people who witnessed an event.
Physical evidence refers to any material items that would be present at the crime
scene, on the victims, or found in a suspect’s possession.
Trace evidence refers to physical evidence that is found in small but measurable
amounts, such as strands of hair, fibers, or skin cells.
What will evidence collected at a scene do for the investigation?
• May prove that a crime has been committed
• Establish key elements of a crime
• Link a suspect with a crime scene or a victim
• Establish the identity of a victim or suspect
• Corroborate verbal witness testimony
• Exonerate the innocent.
• Give detectives leads to work with in the case
Source: http://www3.sc.maricopa.edu/ajs/crime_scene_technician.htm
Crime Scene Personnel
POLICE OFFICERS are typically the first to arrive at a crime scene. They are
responsible for securing the scene so no evidence is destroyed and detaining
persons of interest in the crime.
The FORENSICS UNIT documents the crime scene in detail and collects any
physical evidence.
The CROWN ATTORNEY is often present to help determine if any search
warrants are required to proceed and obtains those warrants from a judge.
The MEDICAL EXAMINER (if a homicide) may or may not be present to
determine a preliminary cause of death.
SPECIALISTS (forensic entomologists, anthropologists, or psychologists) may be
called in if the evidence requires expert analysis.
DETECTIVES interview witnesses and consult with the Forensics unit. They
investigate the crime by following leads provided by witnesses and physical
evidence.
Source: http://science.howstuffworks.com/csi.htm
Crime Scene Protocol
Step 1: Interview
The first step in investigating a crime scene is to interview the first officer at the scene or the
victim to determine what allegedly happened, what crime took place, and how was the
crime committed. This information may not be factual information but it will give the
investigators a place to start.
Step 2: Examine
The second step in the investigation of a crime scene, which will help identify possible
evidence, identify the point of entry and point of exit, and outline the general layout of the
crime scene.
Step 3: Document
The third step in the protocol involves creating a pictorial record of the scene as well as a
rough sketch to demonstrate the layout of the crime scene and to identify the exact
position of the deceased victim or other evidence within the crime scene.
Step 4: Process
This is the last step in the protocol. The crime scene technician will process the crime scene
for evidence, both physical and testimonial evidence. It is the crime scene technicians
responsibility to identify, evaluate and collect physical evidence from the crime scene for
further analysis by a crime laboratory.
Adapted from http://www.feinc.net/cs-proc.htm
Investigating the Evidence
Drug Chemistry – Determines the presence of controlled substances and the identification
of marijuana
Trace Chemistry - Identification and comparison of materials from fires, explosions, paints,
and glass.
Microscopy – Microscopic identification and comparison of evidence, such as hairs, fibers,
woods, soils, building materials, insulation and other materials.
Biology/DNA – Analysis of body fluids and dried stains such as blood, semen, and saliva.
Toxicology – Tests body fluids and tissues to determine the presence of drugs and poisons.
Latent Prints - Identification and comparison of fingerprints or other hidden impressions
from sources like feet, shoes, ears, lips or the tread on vehicle tires.
Ballistics (Firearms) – Study of bullets and ammunition through the comparison of fired
bullets, cartridges, guns, and gunpowder patterns on people and objects.
Toolmarks – Examines marks left by tools on objects at a crime scene or on a victim, such
as a hammer used to break a door or a screwdriver used to pick a lock.
Questioned Documents - Examination of documents to compare handwriting, ink, paper,
writing instruments, printers, and other characteristics that would help to identify its origin.
Source: http://www.isp.state.il.us/forensics/
What evidence would you collect?
Mock Crime Scene: http://www.masss.gov
Let the evidence
speak for itself.
Presentation developed by T. Trimpe 2006 http://sciencespot.net/
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 states that "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
Evidence Examples
Tiny Pieces of
Evidence
Paint
• Physical and chemical analysis of paint evidence (chips or residue) can indicate it’s class,
such as automobile paint, house paint, nail polish, etc. The evidence can be compared to
40,000 different types of paint classified in a database, which can be used to identify a
particular make or model of car or brand of tool.
• 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
Glass
• Glass particles can be found at various crime scenes, such as breaking and entering, hit
and run, vandalism, or murder.
• Glass at a crime scene is analyzed to determine its color, surface characteristics, tint,
thickness, density, chemical composition, and refractive index (RI).
• The results of the tests provide clues about the crime and help investigators connect the
evidence to a suspect or other object used in a crime, such as matching glass from a crime
scene to a headlight to a suspect’s car.
CSI Glass
Analysis
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
Explosives
• Explosive substances can be examined to 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.
CSI &
Explosives
Image: http://www.state.nj.us/njsp/divorg/invest/criminalistics.html
Ballistics
• Characteristics of ammunition, firearms, and residue are examined to find matches
between suspects and the evidence found at a crime scene.
• Chemical tests can reveal gunshot residue (GSR) on the hands, face, or clothing of a
victim or suspect to 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.
Learn more about
ballistics …
Image: http://www.geocities.com/j_ksinha/img/mid1.gif
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.
Microscopic Image of Sand
• Investigators examine the samples for chemical
composition, pollen, plant material, and other organic
matter to find links to a specific crime scene.
Fingerprints
• There are 3 types of fingerprint patterns: arches, loops, and whorls.
Investigators also identify unique ridge characteristics in a fingerprint that
can be used to identify a suspect or victim.
• AFIS (Automated Fingerprint Identification System) is a 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
Impression Evidence
Shoeprints & Tire Tracks
• Impression evidence can be photographed, lifted with tape, or cast with
plaster to compare to a suspect’s shoes or tires.
• Investigators will examine the evidence to identify the brand of shoe or tire based on its
tread pattern and other physical features to provide leads in the case.
• Shoes and tires will also show wear patterns after being used for a period of time as well as
other features (scratches, nicks, and cuts) that can be used to match evidence to specific
items. For example, shoeprints can be matched to a suspect based on how the treads on the
shoes that are worn down due to that person’s walking style.
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 can often be matched to dental records.
Tool Marks
• Tiny nicks and chips form on the edges of a tool as it is used, which
can be used to identify matches between evidence and suspects.
• Tools may also pick up traces of blood or other substances that can
be tested or 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
Fracture Matches
• When an object broken, torn, or cut, two unique edges are formed, which are referred to as
fracture lines.
• These edges can be compared by the naked eye or with microscopes to see if they fit
together , which indicates that they may have been part of the same object at one time.
• Investigators may compare the edges on pieces of tape, glass fragments, paint chips, pieces
of a car from an accident, paper bag, etc. to find possible matches.
Duct Tape
Evidence
Images: http://www.modernmicroscopy.com/main.asp?article=11&print=true&pix=true
Wounds
• Wounds can often be 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.), and
positions of the victim and suspect at the time of the incident.
Questioned Documents
• Examiners will analyze a ransom note or other document to
find clues to link it to a crime scene or a specific suspect. They
will analyze the type of paper used, printing method or
handwriting style, and type of ink.
FBI
Questioned
Documents
UNIT
• Other unique features, such as watermarks on stationary or
indentations made as someone wrote on a page in a notebook,
may provide useful clues.
Image: (Bottom Left): http://dofs.gbi.georgia.gov/vgn/images/portal/cit_11783501/81672146questioned%20document.jpg
Insects
• Flies, beetles, and other insects can provide useful clues about a corpse.
• Forensic entomologists use factors such as weather conditions, the location
and condition of the body, and their knowledge of the life cycles of insects to
help them estimate the postmortem interval or PMI (the time between death
and the discovery of the body).
DNA
• Investigators can extract DNA from almost any tissue, including hair,
fingernails, bones, teeth and body fluids. The DNA is used to create a
profile that can be compared to profiles from suspects or victims.
• 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
Skeletal Remains
• Forensic anthropologists analyze skeletal remains to determine
four characteristics for a victim: age, sex, race, and stature
(height/build).
 Sex - Determined by examining the pelvis, humerus, and
femur
 Age and stature – Determined by analyzing the development
of the teeth, bone growth, and the length of specific bones,
such as the femur.
 Race – Determined by 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 can be used at a crime scene to 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.
 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
Hairs & Fibers
• Hairs and fibers may be transferred from the suspect or the suspect’s
clothes to the victims’ and vice versa. For example, a suspect may
pick up carpet fibers on his shoes or leave hairs behind at a crime
scene.
• Hairs can be examined to identify their origin, such as human or
animal. Hairs with roots intact can be tested for DNA.
• Fibers are used to make clothing, carpeting, furniture, beds, and
blankets. They may be natural fibers from plants or animals or
synthetic fibers that are man-made.
Microscopic Image
of Hairs & Fibers
How is DNA used to solve crimes?
T. Trimpe
http://sciencespot.net/
What is DNA?
DNA stands for deoxyribonucleic acid and contains genetic information. It is
found on chromosomes located in the nucleus of our cells.
What makes up DNA?
• The sides or backbone of the DNA
molecule are made up of sugar
(deoxyribose) and phosphate molecules.
Double Helix
• The rungs that form the middle of the
molecule are made up of pairs of
nucleotides or nitrogen bases. Adenine
(A) pairs with thymine (T), while
guanine (G) always pairs with cytosine
(C).
• The order of the bases determines the
genetic code.
DNA Image: http://science.howstuffworks.com/genetic-science/dna-evidence.htm
How is DNA used as evidence?
• Each person’s DNA is different from other people (except identical twins).
• DNA collected from a crime scene can either link a suspect to the evidence or
eliminate a suspect, similar to the use of fingerprints.
• DNA can identify a victim through DNA from relatives, even when no body can
be found.
• DNA can link crime scenes together by linking the same perpetrator to different
scenes locally, statewide, and across the nation.
• DNA can place an individual at a crime scene, in a home,
or in a room where the suspect claimed not to have been.
• DNA can refute a claim of self-defense and put a weapon in
the suspect's hand.
• It can change a story from an alibi to one of consent.
DNA Strand Image & information : http://www.dna.gov/audiences/investigators/know/
What factors affect DNA evidence?
Several factors can affect the DNA left at a crime scene, such as environmental
factors (e.g., heat, sunlight, moisture, bacteria, and mold). Therefore, not all DNA
evidence will result in a usable DNA profile. Further, DNA testing cannot identify
when the suspect was at the crime scene or for how long.
What is CODIS?
CODIS stands for COmbined DNA Index System, which is an electronic database
of DNA profiles that can identify suspects. DNA profiles from individuals convicted
of certain crimes, such as rape, murder, and child abuse, are entered into CODIS
and help officers identify possible suspects when no prior suspect existed.
Did you know?
Each human cell contains three billion DNA
base pairs. Our unique DNA amounts to 0.1%
or 3 million base pairs.
DNA information : http://www.dna.gov/audiences/investigators/know/
Pros & Cons of
Testimonial Evidence
Presentation developed by T. Trimpe 2006 http://sciencespot.net/
What is testimonial evidence?
Testimonial evidence includes oral or written statements given to
police as well as testimony in court by people who witnessed an
event.
Eyewitness accounts can be a useful tool in helping investigators
with analyzing a crime scene, but are not viewed to be highly
reliable. In addition, eyewitness identifications (right or wrong) can
have a big influence on the outcome of an investigation or trial.
People are likely to view the same scene in different ways
depending on their positions, line of sight, familiarity with the area,
and other factors that can interfere with a person’s ability to
remember details.
The Bunny Effect
CBS News Video
Memory Challenge
Directions:
You will have 30 seconds to view the next screen.
Try to memorize all 20 items you see!
You are NOT allowed to write anything down
You CANNOT talk to anyone else.
Items to remember ...
Neuroscience for Kids - http://faculty.washington.edu/chudler/puzmatch1.html
What do you remember?
You have 2 minutes to list as many of the items as you can!
How did you do?
All 20 – Awesome
15-19 – Great
10-14 – Pretty swell
5-9 – Could be better
4 or Less – Wake up
Did you know?
According to The Innocence Project (2008)
"Eyewitness misidentification is the single greatest
cause of wrongful convictions nationwide, playing a
role in more than 75% of convictions overturned
through DNA testing." Still, the criminal justice
system profoundly relies on eyewitness identification
and testimony for investigating and prosecuting crimes
(Wells & Olson, 2003).
What factors affect a person’s memory
and their ability to identify a suspect?
Source: http://www.helium.com/items/1276135-accurate-eyewitness-accounts
Witness Factors
• Age may play a role in the accuracy of an eyewitness’ statement or
identification of a suspect. Studies have shown that when a lineup
contains the actual culprit, both young children and elderly perform well,
but when the lineup does not contain the culprit there is a higher rate of
mistaken identifications.
• The race of the witness may also play a role. The Cross Race Effect
(CRE) is a phenomenon in which people are better at recognizing faces
of their own race rather than those of other races.
• The use of drugs can alter a person’s ability to recall the events of a
crime even after they are no longer under the influence.
• A person’s memory of an event can be influenced by other witnesses,
investigators, and/or the media. Investigators use open-ended questioning
and follow procedures for conducting line-ups to limit their influence on
a witness’ memory of an event or identification of a suspect.
Source: http://www.helium.com/items/1276135-accurate-eyewitness-accounts
Crime Scene & Suspect Factors
• A crime that is extremely traumatic for an eyewitness may affect his/her
recall of the event. For example, a witness confronted with a weapon
tends to focus on the weapon rather than the perpetrator’s face.
• Someone who is able to focus on a perpetrator's face for a minute or
longer will tend to have a more accurate memory than someone who saw
the person for only a few seconds.
• Studies have shown that faces that are either highly attractive, highly
unattractive, or distinctive are more likely to be accurately recognized.
Simple disguises, such as hats or sunglasses, can interfere with accurate
eyewitness identification. However, body piercings and tattoos increases
the likelihood of an accurate identification.
• The time of day in which the crime occurred as well as a person’s view
of the scene may affect what a he/she is able to see. In addition, a person
who is familiar with the area in which the crime took place, may have a
better recall of the positions of the victims or suspects.
Source: http://www.helium.com/items/1276135-accurate-eyewitness-accounts
The CSI Effect
• Three years ago in Richmond, Va., jurors in a murder
trial asked the judge whether a cigarette butt found
during the investigation could be tested for links to the
defendant. Defense attorneys had ordered DNA tests
but had not yet introduced them into evidence. The
jury's hunch was correct — the tests exonerated the
defendant, and the jury acquitted him.
• In Arizona, Illinois and California, prosecutors now use
"negative evidence witnesses" to try to assure jurors
that it is not unusual for real crime-scene investigators
to fail to find DNA, fingerprints and other evidence at
crime scenes.
• In Massachusetts, prosecutors have begun to ask
judges for permission to question prospective jurors
about their TV-watching habits. Several states already
allow that.
• Last year in Wilmington, Del., federal researchers
studying how juries evaluate scientific evidence staged
dozens of simulated trials. At one point, a juror
struggling with especially complicated DNA evidence
lamented that such problems never come up "on CSI."
The CSI Effect
“Our criminal justice system must find
ways to adapt to the increased
expectations of those whom we ask to cast
votes of ‘guilty’ or ‘not guilty’.
http://www.all-about-forensic-science.com/support-files/csi-effect.pdf