Types of Evidence

“You can observe a lot by just watching.”

-Yogi Berra

• What is evidence? (review notes!!)– Something that tends to disprove or establish a

fact. – Includes

• Documents• Testimony • Objects

Two types of Evidence• Testimonial Evidence

– includes oral or written statements given to police as well as testimony in court by people who witnessed an event.

– Statement made under oath– What is said in court by a

competent witness– Also called direct evidence or

prima facie

• Physical Evidence– Tangible items that tend

to prove some material fact

– Aka real evidence

Testimonial evidence• Eye witness accounts provide important evidence• Eye witnesses Heavily influence juries• Fear and stress involved in witnessing a crime can either sharpen the senses or confuse

them• But are they accurate?

– New information affects eye witness accounts• Mug shots• Leading/Suggestive questions

– Can change memory of witness, even those trying to be fair or honest– Memory errors

• Time between the crime and questioning of witness can affect what they remember– Perception errors

• Too dark• Encounter too brief• Presence of weapon diverted witnesses attention

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.

Memory Challenge

Neuroscience for Kids - http://faculty.washington.edu/chudler/puzmatch1.html

Items to remember ...

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

Points to consider in Reliability of Eye Witness Accounts• Type of crime and how witness saw

it– Research shows witnesses are

better at remembering certain characteristics (hair color and sex) than others (age, height ,and specific race)

– If witness is physically similar to offender, they will give a more accurate account

• Victims of serious crimes sometimes have more accurate memory over long periods of time– Relive event– Presence of weapon=sharpen

sense/awareness

• Some types of witnesses are better at remembering than others– Children– Older adults– Learning disabilities and

mental disorders– Alcohol and drugs– Head injury

• Interviewing Techniques or How information is retrieved can make a difference in accuracy of witness’s account• Witnesses are better at answering questions about what

happened than answering questions regarding description of offender

• Open-ended questions get better answers– Careful choice of words influence memory– Ex. Ask witness to describe what defendant was wearing

rather than what color was his shirt– What would be a bad question?

Other important factors when weighing an eye witnesses account

• Relationship of witness with the accused• How much time passed between offense

and identification• Whether the witness already identified

the (or failed to identify) the defendant• Whether the witness has already

identified someone else****most known cases of an innocent

person being convicted happened because of a mistaken eye witness

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).

Source: http://www.helium.com/items/1276135-accurate-eyewitness-accounts

Did you know?

What factors affect a person’s memory and their ability to identify a suspect?

Crime Scene Challenge

• Now that your eyes and brain are warmed up, let’s test your observation skills a bit more.

• You will have 2 minutes to study the photograph of a crime scene on the next slide.

• Try to pay attention to details as you will be asked 10 questions about the crime scene!

• You are not allowed to write anything down until after the time is up.

• Ready?

Answer each question below.

1. What color coffee mug was in the picture? Blue Red Yellow  2. When was the deadline? Yesterday Today Tomorrow 3. What time was on the clock on the wall? 10:40 11:05 1:55  4. How many sticky notes were on the whiteboard? Four Six Eight 5. Which of the following was NOT in the picture? Stapler Trash Can Printer 6. What was the name on the plaque on the desk? Bill Brian Carl  7. What color was the victim's shirt? Black Blue Red 8. How many plants were in the picture? None One Two

9. What was the color of the marker in the desk drawer? Red Blue Green

10. Where was the book in the picture? On a box In the trash can Under the body

Source: http://forensics.rice.edu/html/picture_begin.html

Facial Composites

Investigators work with sketch artists and eyewitnesses to create facial composites, or sketches of a person’s face. Today many police departments are using facial reconstruction software to help them with this task.

The composite may be used internally to assist officers in identifying the suspect or used externally through local media (radio, TV, and newspaper) to solicit leads from citizens.

FACES – A software program that offers many options to help you recreate a person’s facial features.

The shape of the faceThe shape of the jawThe shape of the eyesThe shape of the noseThe width of the neckThe shape & protrusion of the earsThe presence of facial piercingThe presence of facial hair, its color, & locationThe presence of facial markings, such as scars or tattoosForehead or other facial linesThe presence of eyeglasses or sunglassesThe length, color, & texture of the person’s hair

You will have a chance to try to create a facial composite. You will need to pay close attention to the following features:

"Wherever he steps, whatever he touches, whatever he leaves even unconsciously, will serve as silent witness against him. Not only his fingerprints or his footprints, but his hair, the fibers from his clothes, the glass he breaks, the tool marks he leaves, the paint he scratches, the blood or semen he deposits or collects -- all of these and more bear mute witness against him."

—Dr. Edmond Locard

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.

Physical Evidence• Tangible items that tend to prove or disprove a fact• “Real Evidence”• 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. • Type of evidence forensic scientists are most interested in• Forensic scientists will…

– Observe physical evidence– Determine identity– Determine origin

Physical evidence…

• Can be any material or object• Take any form

– Large as a building– Fleeting as an odor– Small as a hair– Microscopic as DNA

• Much more reliable than testimonial evidence

Common Types of Physical Evidence

Drug and toxic substance Resins, plastics Fingerprints

Paints Explosive residues Hair

Gun shot residues (GSR) Serial numbers Tissues

Firearms and ammunition Documents Pollen

Impressions Fibers Wood material

Petroleum products Soil Feathers

Alcohols (esp. ethanol) Glass Bones

Rubber material Blood and other body fluids

Tool marks

Properties of Physical Evidence• Physical

– Can be observed and measured– Physical changes do NOT change the identity of a

substance– Properties that do not change the chemical nature of

matter– Intrinsic/intensive physical properties

• Does NOT depend on the amount of a substance• Examples

– Density– Melting point– boiling point– Freezing point– Viscosity– Refractive index– Malleability– Luster– color

– Extrinsic/extensive physical properties• Depends on amount of substance• Length, volume, mass, weight etc

• Chemical– Properties that do change the

chemical nature of matter– Can be observed when object or

substance changes its chemical composition

– Observed when one substance reacts with another

• ONLY observed during a chemical reaction

– Signs of a chemical change• Formation of gas (bubbles)• pH change• Change of color (indicator)• Formation of precipitate• Change of smell

– Examples• Digestion• Respiration• Photosynthesis• Combustion• decomposition

• Determining origin of a substance almost always involves a comparison of object or substance itself with something similar or with something similar that the scientist knows the origin of

• Compare with a known or “control”

The Innocence Project

• National organization dedicated to exonerating wrongfully convicted people through DNA evidence

• Eye witness misidentification is the number one cause of wrongfully convictions nationwide

• As of 2008, the Innocence Project exonerated 212wrongfully convicted poeple

Types of Physical Evidence

• Trace Evidence• Transient evidence• Conditional Evidence• Indirect Evidence• Circumstantial Evidence• Individual evidence• Class evidence

Trace Evidence• Trace evidence refers to physical evidence that is found in small but measurable

amounts, such as strands of hair, fibers, or skin cells.

Not all evidence is permanent…• Transient evidence

– Temporary evidence– Can be easily changed or lost– Usually observed by first officer on scene and must be recorded at that

time• Examples?

– Odors• Perfume, cigarette smoke, gas

– Temperature• Coffee pot, car hood, water in bath tub, dead body

– Imprints• Footprints in sand, fingerprints in dust, teeth marks in perishable

food

Conditional Evidence• Produced by a specific action or event at the

scene • Must be observed and recorded• Examples

– Lights– Garage door– Doors– Windows– Position of body– Position of furniture

Indirect Evidence

• Evidence that does not prove or disprove a fact in question

• Evidence providing only a basis for inference about a disputed fact

• May prove something like the possession of controlled substances or driving under the influence

Circumstantial Evidence

• Evidence based on suggestion rather than personal knowledge

• Implies a fact or event without actually proving it• The more circumstantial evidence there is, the greater it

weighs• Probability and statistics important• Examples

– Blonde hair found in hand of murder victim with black hair– Size 10 sneaker print near the body– Both of these limit the pool of suspects

Value of Physical Evidence• Can prove crime has been committed

– Gasoline at a scene of a fire• Back up witness testimony or disprove it

– Test blood stains of suspects• Link suspect with victim or crime scene

– Broken glass of headlight in cuff of suspects pants at scene of hit and run

• Determine identity of people associated with crime– Fingerprints, DNA

• Allow investigators to reconstruct a crime– Blood spatter patterns

Significance of Physical EvidenceIndividual Evidence• Material that can be related

to a single source • Individualization always

involves a comparison• Narrows an identity to a

single person or thing• Examples

– DNA– Fingerprints– Handwriting– Some physical evidence

• Piece of glass that fits another piece like a jigsaw puzzle

Class Evidence• Material that can be associated with

a group of items that share properties or characteristics

• Object is similar to group of similar objects but not one single object

• Narrows an identity to group of persons or things

• Examples– Blue jeans

• We can use some individualization such as length, style, brand, shade, surface treatment but there are still thousands of jeans like that

Evidence

Direct Circumstantial

Physical Biological

Evidence Examples

Did you know? Most paint evidence submitted to a lab will come from hit-and-run cases involving automobiles.  

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 Layers Physical Match of Paint Chip Edges

Paint Transfer on a Car

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.

The pattern of cracks in a windshield fracture can reveal information about speed, occupant position, and angle of impact. Magnified image of glass fragments

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.

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 National Integrated Ballistics Identification System (NIBIS) database to compare markings from bullets, cartridge cases, and shotgun shells to ballistic evidence.

Investigators can compare the striations on bullets to see if

they match.

Did you know? Caliber (handguns & rifles) or gauge (shotguns) refers to the size of the internal diameter of a gun’s barrel.

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.

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.

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.

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.

Images: http://biology.arizona.edu/sciconn/lessons2/Vuturo/vuturo/photos/desmus.gif

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.

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://www.tcamb1.com/images/hairanalysis.jpg and http://www.npsg.uwaterloo.ca/resources/images/microscope/Sand%200004.jpg

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.

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

Microscopic Image of Hairs & Fibers

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

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.

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.

• Other unique features, such as watermarks on stationary or indentations made as someone wrote on a page in a notebook, may provide useful clues.

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.

Mock Crime Scene: http://www.masss.gov

What evidence would you collect?

Testing Physical Evidence• Questioned sample (Q)

– Material collected from known location but of unknown origin

• Known sample (K)– Material that comes from a proven or known source

• Control Sample– Material that is similar to the questioned sample and

known samples and is used to validate the test method and procedure

– It is expected to respond in a certain way in testing– Used to validate method of testing by comparing test

results to those of the questioned and known sample• Questioned sample is compared to a known sample

ExampleInvestigator find paint of unknown origin on bumper of vehicle that is suspected to be involved in a hit-and-run (unknown origin)It would be compared to paint of victims bicycle (known origin)

When paint is heated, depending on type, it can induce a color change

Different types of paint from known origins would be the control sample(s)Same types of paints would change same colors (or not change)

A control test would be run on control sample paints to verify method and procedureIf control paints (from different known origins that would eliminate the suspect) did not change color in a test, but Q and K both changed the same color, there is a high probability that the Q and K paints originated from the same source, therefore linking the evidence on the car to the hit-and run

Probability and Class Evidence• A young person is seen leaving the HGHS student

parking lot after being near a car with a broken window. The car’s CD player is missing. The suspect was identified as having light brown hair and having long sleeves, khaki pants, and dark sneakers. In a school of 1,600 students, how common are these characteristics?

• How many students would be expected to be wearing longs sleeves on any given day? Our class has __ students, __ are wearing long sleeves. How many students in the school are likely to be wearing long sleeves?

• # in class wearing white/# of students in class=?• How many students is ___% of the whole student

body?– Decimal form of percent x 1,600 students=____students

• So if our class is a representative of the whole school, then you expect ____students to be wearing long sleeves today. Is this good evidence? Can you do better?

• How many students would be wearing khaki pants? How many students in our class have khaki pants on today?____

• What is the percentage of students in our class with khaki pants on?– # of students in khaki pants/# of students in class=?

• How many students in school would be wearing khaki pants?

• How many students is ___% of the whole student body?– Decimal form of percent x 1,600 students=____students

wearing khaki pants– Is this good evidence? Could we do better?

• How many students are wearing khaki pants and a long sleeves?– (decimal) of long sleeves x (decimal) of khaki pants=

____ (decimal) – Multiply above decimal by 100% to get # of students in

class wearing long sleeves and khakis• Now multiply the above # (decimal form) by 1,600

students in school– This gives us number of students in school wearing both

khaki and long sleeves• We have narrowed the field immensely by just 2

general pieces of class evidence

• Now determine how many students would be likely to have light brown hair.– # of lt. brown hair in class/# of students in class= # in

class with lt. brown hair• How many students in school with light brown hair?

– Above decimal x 1600 students=# of students in school with light brown hair

• How many students with long sleeves, khakis, and light brown hair?– Long sleeve decimal x khaki x light brw hair x 1600

students=____ (decimal)• So how many in whole student body meet all

those?– Above decimal x 1600=___ students

• We have narrowed 1600 suspects to ____ students. • Last one!• How can four pieces of class evidence affect

probability of nailing down one?• How many students with dark sneakers?

– # of students in class with dark sneaker/# of students in class=____(decimal)

• How many students in school with dark sneakers?– Above decimal x 1600 students=____students with dark

sneakers

• How many students in school likely to be wearing long sleeves, khakis, have light brown hair and black sneakers? (decimal long sleeves) x (decimal khaki) x (decimal of lt.

brwn hair) x (decimal of black sneakers) x 1600 students=___students!

Increase Probative value of class evidence!

• A way to increase probative value of class evidence is to find as many different types of objects as possible with which to link the suspect to the crime or the victim.– Probative: (supplying proof or evidence)

• Soil and red paint on jeans each alone belong to large class of material

• But both occurring together increases the probability of linking the jeans with a certain crime even though the evidence is circumstantial

• Probative value grows by considering class evidence• “the Product Rule”

– Term for this type of statistical evidence– Only works for independent events or observations– Example: students encouraged to wear school colors

green and black, students wearing green and black would be related and not independent

• Class evidence is useful is there is a significant amount for a given case

• Also useful for eliminating or exonerating certain suspects– Blood stain is type O, most common, other blood types

A, B, and AB can be eliminated as possibilities

Securing and Collecting Evidence• Evidence must be properly packaged, sealed, and labeled• Liquids and arsons

– Air tight, unbreakable container

• Biological evidence– Breathable containers so evidence can dry out– Prevent mold, kept in freezer

• Placed in Paper bindle• Bindle placed in plastic/paper container• Sealed with tape, signature on top• Evidence log and chain of custody attached

Evidence Log

• Contains the following info– Case #– Item Inventory #– Description of evidence– Name of suspect– Name of victim– Date and time of recovery– Signature of person recovering evidence– Signature of any witness present during collection

Packaging Evidence• Size of bindle depends on evidence

– Small• Piece of sheet paper

– Large• Large sheet of wrapping paper

• Packaging techniques– Choose appropriate size of sheet paper for bindle– Crease paper (9 squares)– Place evidence in center square– Fold left and right sides in– Fold in top and bottom– Insert top flap into bottom flap and tape closed– Place bindle into plastic or paper evidence bag and fold bag closed– Place seal over folded edge of evidence bag– Have collector write their name over the folded edge

• Wet evidence– Place in paper container and allowed to air dry– Wet evidence should NEVER be packaged in plastic container when wet (any DNA will degenerate

and evidence may become moldy and useless)• Controls must be obtained from victim and crime scene and package accordingly

Sketching the Scene• Note position of body• Position of evidence• All evidence should be measured from 2 IMMOVABLE objects• Label North• Scale of distance provided• Include anything in vicinity of crime scene

– Windows, doors, furniture• Outdoor crime scene

– Position of trees, hedges, vehicles, other structures • Final copy of crime scene sketch can be made from original

– Computer programs

• Turn In Today:– Medical Examiners Report/Police report

• List time, location, witnesses, etc.• Diagram/sketch of your crime scene and location of each piece of

evidence (numbered)– Bags with Evidence Labeled– Evidence Collection Sheet

• Evidence Numbered (from diagram) and each of the following labeled :– A. CLASS or INDIVIDUAL and EXPLAIN WHY!!!– B. Branch of the Crime lab that would be used to analyze evidence

• What Must Be Included…at least 3 of each of the following:– Transitional– Conditional– Large physical– Trace Physical– Trace biological (DNA, hair, blood, fingerprint, tissue, plants, bacteria, etc)– Testimonial

Group Work• Crime scenes• 16-18 A; 13-15 B; 10-12 C; 7-9 D; 0-6 F

3 (excellent, all included)

2 (average, missing a few parts)

1 (minimal, missing more than half the required points)

0 (not present at all, completely off topic/wrong classification)

Hard copy with all planted evidence in their crime scene listed

Identifies each piece if evidence as either class or individual

States the crime lab unit that would analyze evidence

Includes at least 3 of each evidence type (physical large, physical trace, conditional, transitional)Location of evidence listed on hardcopy and samples collected in ziplocs

Overall creativity of crime scene