Essential Question: How did evidence collection and examination help solve the Bundy murder cases?
Evidence:
Witness accounts
Marks from weapons
Fingerprint smudges
Blood evidence
A bite mark
Types of Pattern Evidence
Focus Question: What are examples of pattern evidence?
Types of Impressions:
Bitemarks: Forensic experts can make a model of bite marks to compare a wound on a victim to a potential suspect.
Footprints: They can make a cast of a shoe tread left in a sole or flooring to compare to the shoes of a suspect or victim.
Tire Tracks: They can leave an impression in soils that can be compared to the suspect’s vehicle.
Toolmarks: They leave impressions when they come in contact with surfaces or the human body. A tool mark can be compared to a tool owned by a suspect.
Fingerprints: Can be photographed or collected from a crime scene and compared to a suspect’s prints.
Blood Spatter: The body releases a pattern of blood during an injury that depends on the mode and force of the injury. Blood spatter patterns give investigators more information about what happened during a crime.
Pattern evidence is often considered circumstantial until supporting evidence can validate it. A tire tread that matches a suspect's car is circumstantial without an eyewitness.
Casts and Impressions
Essential Question: How do impressions help forensic scientists?
Forensic scientists can use casts and impressions if unable to gain a reproduced bite mark willingly.
It's All in the Teeth
Focus Question: How can teeth impressions be used as evidence?
Documentation of bite impressions:
Take an image as soon as the bite mark is noticed. Take multiple pictures at different angles to ensure accuracy.
Place a ruler over the mark during imaging to help ensure proper measuring if the mark changes over time.
Outline each tooth mark on the picture(s).
Identify the tooth type for each impression.
Note any variations in tooth angle or arrangement.
Bite Mark Anatomy:
Odontologists expect to find basic dental anatomy in a bite mark, such as molars in the back of the mouth and incisors towards the front.
A tooth's size and structure will determine how a bite mark will look in different substrates.
Molds: Once a suspect is identified, a mold is taken of their mouth. First, the impression substrate is added to a plastic tray. Then the plastic tray is placed around the top and bottom teeth and gums and pressed into place.
Casts: A mold impression is filled with plaster to create the exact void of the teeth in the plastic tray. This is the cast of the teeth. They are used to recreate a crime scene bit marks, then determine if a match exits
Unlike Bundy, more people today have straight teeth due to the decreasing cost of dental care. Therefore, a bite mark made with straight teeth will be less confirmatory evidence.
Collecting Impressions
Focus Question: How are impressions collected from a crime scene?
Types of Prints:
Patent:
Visible
Two-dimensional
Latent:
Not visible until processed
Two-dimensional
Plastic:
Visible
Three-dimensional
Collection Methods:
Photographing Impressions:
Include a ruler in the picture for the sizing of the impression.
Once they are printed or digitized, they mark the photo with measurements that relate to the location of the impression to other evidence pieces.
Casting Impression:
When a 3-D impression exists, a putty is added to make a cast.
It can recreate a footprint or other mark collected.
Electrostatic Dust Lifter:
When a footprint is hard to see, a forensic scientist can get an image by pulling dust or other small particles from the print's surface.
First, they charge a black plastic film with electricity and place it over the footprint. The dust attracts to the film and they stick to it
Casts and impressions may be used as demonstrative evidence in court.
All About Patterns
Focus Question: How are tire tracks and footprints used as evidence?
Variables that affect a tire's tread:
Tire Track Traits:
Wear:
Explanation: can help match the tire to a specific car more accurately. Tires wear differently based on driving surface, technique, and the amount of air in the tire.
Tread Depth:
Explanation: tread on tires wears down over time. The tread depth will impact the impression and help with identification.
Speed:
Explanation: It can indicate if they stopped at the scene or sped away. If tracks are well defined, a car is moving slowly. If the tracks are smudged and less defined, the vehicle is moving faster.
Pattern:
Explanation: using a database, they attempt to match the tire track to its matching tire. Lastly, they list vehicles that use the same type of tire.
Footprints:
Type of Shoe:
Explanation: Can indicate the type of shoe worn or if the suspect was barefoot
Gait and Path Taken:
Explanation: The way a person walks or runs can help tie a footprint to a person and help explain what was happening during a crime. The direction also helps with creating a timeline of the crime.
Weight of Person:
Explanation: The deeper the print, usually the heavier the person.
Some types of trace evidence from tire tracks and footprints are soil, paint, pollen
Lesson Review
Question 1: How would you collect evidence from this footprint?
Answer:
Take a picture with a ruler in the image
Make a cast of the impression
Use the cast to recreate the footprint
Compare to the suspect's shoes
Question 2: How would you obtain evidence from these footprints?
Answer:
Take a picture with a ruler in the picture
Use electrostatic dusting technique to get full footprint image
Compare the image to the suspect's shoes
Question 3: What conclusions can you make about this tire track?
Answer:
The tires have deep treads.
The vehicle would be large and heavy.
The car seems to have been going slowly.
Tool Marks
Essential Question: What are tool marks, and how are they used as evidence?
Evidence in the MacDonald family case:
A knife
Bloody splinters
Digital fingerprint
Bloody footprints
Wounds in the wife’s chest
Making Marks
Focus Question: What information can a tool mark tell a forensic scientist?
Weapons and Their Marks:
Pry Bar:
Marks: Pry bars have two prongs at the front, making a distinct mark. Some prybars are coated with paint that can also transfer to the mark.
Screwdriver:
Marks: The primary mark that usually shows up for comparison is the end bit.
Hammer:
Marks: Their mark is almost always circular. The main impact comes from the center of the hammer's head.
Chisel:
Marks: Similar to a flathead screwdriver, but one side is thinner than the other, as this tool is used for cutting and scraping. The mark made by this tool is generally flat and deep.
Knife:
Marks: Can make different marks, depending on its angle during use. For example, a slice looks different than a stab. In some cases, a piece of a knife can break off and be used to solidify a match.
Razorblade:
Marks: Similar to knife slit marks but usually have thinner resulting lines. They can exist as a single blade or within an apparatus like a box cutter.
Bat:
Marks: Can leave distinctive marks and even transfer material to another object. For example, a bat or club usually makes a blunt mark.
Bullets:
Marks: The impact makes a mark to help identify a particular gun. The barrel of a gun also marks the bullets as they are fired. These marks are called striations.
Mark Evidence
Focus Question: How is tool mark evidence collected?
Tool Mark Collection Techniques:
Attempt to ensure the tool mark is from the crime itself. For example, some marks could be from replacing a lock or a misjudgment during a project.
Take a picture of the evidence with a ruler in the picture.
If possible, collect the actual evidence with the tool mark.
If unable to collect the actual object, make a cast of the tool mark impression.
Record observations around that tool mark that may help explain how the tool was used. Some tool marks point to a group of possible tools used in the crime. Other tool marks might have individual characteristics that match an exact tool owned by a single person
Mark Analysis
Focus Question: How is tool mark evidence analyzed?
In the lab, scientists evaluate tool marks or casts using a microscope. The details are documented with measurements and pictures.
Tool Mark Databases:
NRBTD Database (National Institute of Standards and Technology):
NSIT Provides an open-access database of tool marks data. It contains microscopic images & three-dimensional surface images of tool marks collected by NIST or other database users.
NIBIN Database (National Integrated Ballistic Information Network):
Compares images of submitted ballistic evidence from shooting scenes and recovered firearms and creates a list of possible similar results. A trained NIBIN technician then conducts a correlation review of the results to find potential matches to firearms
Lesson Review
Type of evidence in the MacDonald family case and how it helped solve the case:
Bloody Footprints
Helped investigators find out when the crime happened. Since they only came out of the daughter’s bedroom it didn’t happen in the living room
Bloody Splinters
Matching splinters on the wounds of his daughter and wife were found on his. The splinters matched a wooden club that his wife had used to help knock bed pieces into place the week before.
Knife
The knife appeared to be strategically placed. It did not have prints. The blood on it seemed to have been placed on the blade afterward.
Wounds in wife’s chest
The wound in the wife's chest was not consistent with the knife found at the scene. However, an ice pick matched the wound and blood type of the wife.
Use of Fingerprints
Essential Question: How can fingerprints be used in an investigation?
Fingerprints make each person unique and help forensic scientists solve a crime.
Fingerprint Basics
Focus Question: What makes a fingerprint unique?
Lumps of stem cell tissues called volar pads are thrown under the skin of each finger. The PAD size and orientation are genetic, therefore many relatives share patterns.
Embryonic skin layers grow at several layers. Details on how the lines grow ono the person's fingers depends on many factors, such as nerves and capillaries, fluid pressure and even direction the fingers are orientated relative to gravity.
The average person has 50 forks on each fingerprint.
There are 80 billion fingerprints in the world.
Patterns on Fingerprints:
Delta:
Characteristics: Triangular area in a fingerprint where the ridges radiate in three directions
Arch:
National Percentage: 5% of all fingerprints
Pattern: Flow in from one side and flow out the opposite
Number of Deltas: 0
Loop:
National Percentage: 60%
Pattern: Ridges flow in from one side and flow out the same side
Number of Deltas: 1
Whorl:
National Percentage: 35%
Pattern: Ridges flow in series of circles and loop around a center
Number of Deltas: 2
Collecting Fingerprints
Focus Question: How are fingerprints collected?
Fingerprint Collection Techniques:
Patent:
Are two-dimensional and are visible to the naked eye.
Made of substances such as ink, blood, and grease
Details:
Photograph or collect with tape or slide.
Store in an envelope in a cooler or refrigerator to preserve biological substances that may be in the fingerprint.
Latent:
Two-dimensional but are not visible unless they are dusted with a special powder or substance. Such as magnetic or UV light.
They are made from sweat and oils on the skin
Details:
Dust surface with a smooth powder.
Photograph or collect with tape.
Use electrostatic dust lifter.
Plastic:
Are three-dimensional that are visible to the naked eye.
Made by pressing a finger against a substance that can hold shape
Details:
Use clay or putty to collect imprints.
Make a cast from the imprint.
Dip cast in ink and recreate fingerprint on paper or photograph.
Fingerprints can change temporarily or get more challenging to recover, but the patterns don’t change.
Fingerprint Tech
Focus Question: How are fingerprints used?
One database is called the Automated Fingerprint Identification System (AFIS) and can compare a fingerprint to millions of sets of fingerprints in a matter of minutes.
Facts AFIS Can Contain:
Prints
Criminal Histories
Mugshots
Scars
Photos of tattoos
Height
Weight
Hair
Eye color
The advantage of electronic fingerprinting is that you can get the result back in a short amount of time.
Three reasons why fingerprints are so helpful to forensic scientists:
Are individual evidence. No one has identical fingerprints
Do not change from the time they develop in the womb
Can be compared to many samples using a database
Glass and Paint Evidence
Essential Question: How can glass and paint be used as evidence in a crime?
Evidence from the Road Rage Incident:
The details of the bullet hole in the window
Pieces of glass on the ground near the deceased man
Small particles in the wound of the dead man
Glass Evidence
Focus Question: Which characteristics of glass are important to an investigation?
Types of Glass and Their Characteristics:
Soda-Lime Glass:
Characteristics:
70% silicon dioxide
15% sodium oxide
10% calcium oxide
5% other oxides
Shatters into smaller pieces with sharp edges
Examples: Used in windows, bottles, and glasses
Tempered Glass (Safety Glass):
Characteristics:
Very strong
Breaks into small pieces with smooth edges
Examples: Found in the side and rear windows of cars
Windshield Glass:
Characteristics:
Consists of 2 layers of glass with a plastic center
Tough to break and expands in hot and cold temps
Examples:
Used as windshield glass in cars and safety glass in banks
May crack but pieces remain attached to plastic
Help keep passengers safe from injuries
Glass contains striations just like fiber and plastic.
When glass breaks, small particles called backscatter are blown and scattered in the direction if the impact.
The resulting lines of cracked glass are called fractures.
Types of Fractures:
Radial Fractures:
Extends outward like the spokes of a wheel
First fracture after impact
Occur on the opposite side of impact
Concentric Fractures:
Forms a rough circle
Second fracture after impact
Occurs on the same side of impact
Number increases with the velocity of the impact
Glass Analysis
Focus Question: How is glass analyzed and collected?
Impact Source:
Explanation: A cone impact will from in the direction of the force
From the outside: If its facing an observer the impact came from the opposite side of the observer
From the same side: If its facing away from the observer, the impact will be on the same side
Angle of Entry:
Explanation: The shape of an impact can indicate the angle of entry
Straight: If the entry of the bullet is straight through the glass, it will make a perfectly round hole.
At an angle: If a bullet enters the glass from the right or left, it will make an oval-shaped hole.
Refractive Index:
Explanation: Measures how light bends as it passes from one substance to another.
Submersion test: an determine the refractive index of small fragments. For example, if a piece of glass disappears in a liquid, it has the same refractive index as the liquid.
Becke lines: If a glass's refractive index is different (either higher or lower) from the liquid medium it's in, a halo-like ring called a Becke line appears around the glass when viewed under a microscope.
Steps to Collect Glass Evidence:
Photograph the scene.
Record observations of physical characteristics of glass.
Collect large pieces of glass with care and store them in boxes.
Place small fragments into paper envelopes or pill bottles.
Label fragments with the distance from impact.
Collect all glass around motor vehicle accidents
Paint Evidence
Focus Question: Which characteristics of paint are important to an investigation?
Analysis of Paint is Based On:
Appearance
Microscope evaluation
Physical Properties
Chemical Properties
Paint can transfer between objects.
Properties of Paint:
Physical Properties:
Color
Layer sequence and thickness
Weathering patterns
Chemical Properties:
Types of pigment
Polymer composition
Additive composition
Paint Characteristics:
Pattern: A void in a painted surface indicates that a chip of paint may have transferred during a crime
Layers: Knowing the layers of paint in a sample can help determine a match to a repainted car or wall with identical paint layers.
Composition: can lead a forensic scientist to its manufacturer. For example, if the paint is from a car, some databases can help identify its make, model, and year. This identification can be made even with a small paint sample.
Paint Analysis
Focus Question: How is paint analyzed and collected?
Methods for Micro-Analysis:
Microscopic Examination: help scientists closely examine paint layers, samples can be placed under a comparison microscope. This allows them to view the layers side by side and check if they match.
Gas Chromatography: Gas chromatography uses heat and gas to break down paint and separate its parts, helping scientists see what it's made of.
UV Spectrophotometry: uses UV light to shine through a paint sample and checks how much light the paint absorbs to identify its pigments.
Steps to Collecting Paint Evidence:
Photograph the scene.
Attempt to take note of any colors or layers seen in the sample.
Collect larger pieces of paint in envelopes and pill bottles.
Collect small particles with tape.
Blood Spatter Patterns
Essential Question: How is blood spatter used in a forensic investigation?
Blood spatter analysis tracks the path blood travels after it leaves the body due to an impact.
Spatter Matters
Focus Question: What inferences can scientists make from blood spatter evidence?
The pattern on blood spatter depends on:
Large or small the injury
Blood pressure
What might have been in the way of the spatter
Types of Spatters:
Passive Blood Spatter: Happens when blood exits the body and lands on a surface due to gravity. It causes the drops to be circular and roughly the same size
Impact Blood Spatter: When the body or the blood encounters a forceful impact. Causes blood to spread out in patterns of tiny- size drops
Transfer Blood Spatter: Blood touches an object and moves into another location. Can be due to a weapon or a person
Blood Spatter Inferences:
Weapon Used: The angle and pattern of blood spatter can help identify the weapon used.
Trajectory of Projectile: The angle and pattern of blood spatter can show the direction of impact. By following the path, experts can figure out where the weapon was and its angle.
Direction of Travel: The direction of blood can show where the victim or suspect was moving.
Number of Wounds: The amount of blood spatter can show how many wounds someone had.
Steps to Collecting Blood Spatter Evidence:
Photograph the scene, making sure to include a ruler for reference
Note the location of blood, any voids in blood, and any objects blood appears on.
Cut out any possible surfaces with blood spatter.
Collect objects with blood spatter on them, including clothes, furniture, and wall paintings.
Spatter Matters
Focus Question: What information do spatter patterns provide?
Blood Spatter Patterns:
High Impact:
Size: droplets are less than 1 mm
Velocity: Estimated at 100ft/sec
Cause of wound: Most often a gunshot
Medium Impact:
Size: droplets between 1mm & 4mm
Velocity: Estimated at 25 ft/sec
Cause of wound: Often from a stabbing or a blunt object
Low Impact:
Size: droplets are more than 4mm
Velocity: Estimated at 5 ft/sec
Cause of wound: Often from a dripping from a wound also called a passive blood spatter
Direct blood droplet characteristics:
Roughly dropped from an angle of 90 degrees
Straight down the body
If found on the wall, came from a horizontal entry point
Angled droplet characteristics:
Can determine the position of an impact based on where the most significant part of the drop is in relation to the trail
Spatter Source
Focus Question: How do forensic experts determine the source of blood spatter?
Blood spatter can be used to approximate where a suspect may have been in proximity to the victim.
Blood Spatter Sources:
Area of Convergence: Experts draw lines following the angles of the blood drops to trace them back to where they came from. The spot where all the lines meet is the Area of Convergence, the place the person was located when they received the injury that caused the blood spatter.
Area of Origin: By looking at where the blood came from and its angle, experts can figure out how high the victim was when hurt. This helps them tell if the victim was standing, sitting, or lying down during the injury.
Additional Facts About Crime Scenes:
Void: Any spots where blood spatter is missing can help determine if an object may have been sitting in the way. These could be a human body or a piece of furniture that was moved.
Source:
Forensic experts look at the angles and sizes of blood drops to find where they came from.
Arterial blood drops are bigger and have a puddle-like shape. Smaller, uneven drops usually come from a vein injury.
Amount:
Higher blood pressure forces more blood out of the body if a person is standing. Conversely, when a person is lying down, their blood pressure is lower. Therefore, less blood would be forced from the body during injury.
This medium impact spatter found low on a wall is more consistent with someone lying or sitting down when struck.
This puddle of blood on the ground is consistent with someone standing, as the pressure would be higher, contributing to more blood loss.
List What a Blood Stain Pattern Analyst Does:
Analyzing the initial crime scene
Photographing the crime scene and evidence
Recording observations and writing reports
Reconstructing crime scenes via sketches and computer software
Forensic Psychology
Essential Question: How can psychology help solve a crime?
A psychological investigation led to the lesser charge for the politician killer.
Criminal Profiling
Focus Question: What information can a criminal profile provide?
Criminal Profiling is a method that seeks to identify a suspect's mental, emotional, and personality characteristics and patterns of behavior based on the things done or left at the crime scene.
Profiling Methods:
Crime Scene Profiling: They look at clues at a crime scene to figure out what happened. For example, marks from a crowbar and footprints near a window might show that a suspect watched the victim for a while before breaking in.
Geographical Profiling: can reveal the habits of a suspect and even reveal the offender's place of residence.
Suspect-Based Profiling: They collect information about a suspect’s feelings, thoughts, actions, and background. This includes things like if the person has habits they can’t control, went through a recent trauma, or is poor. They also look at the suspect’s past, like previous crimes, to understand how they might act in the future.
Psychological Profiling: They study the tools and ways a crime was done to learn about how the suspect works, called their M.O. A suspect’s M.O can show important parts of their personality and life. For example, if they are organized, they might hide weapons to avoid being caught. Psychologists have noticed that organized criminals are often smart, come from stable families, and live normal lives with work and friends.
Psychological Autopsy: They check the health and mental state of someone before they died, especially if it might be suicide. They look at medical records and talk to family and friends to understand how the person was feeling.
Profiling Methods
Focus Question: What methods are used to build a criminal profile?
Profiling Approaches:
The top-down approach starts with a big picture of a crime scene and the suspect. Relies heavily on past experiences of crimes by the investigator
The bottom-up approach starts with the small details of the case. Starts with small details of the case, no assumptions are made
Profiling Level Features:
Top-Down Approach:
Big picture
Small details
Identifies characteristics of an offender from a crime scene
Uses data from previous crimes to categorize a suspect into a type, such as organized or disorganized offender
Bottom-Up Approach:
Small details
Big picture
More scientific and data-based
It is based on evidence collected in the current case
It does not make assumptions based on previous experience
Human behavioral patterns are challenging to interpret across different situations.