WARMUP!!!!!
When I graduate from
high school I want
to…….
UNIT 3
IMPRESSION EVIDENCE
What Causes Impression
Evidence????
When one object presses hard
against another object and
leaves an indentation or print
What kind of impression
evidence can you think
of ?
Tire tracks
Footprints
BITE MARKS
TOOL MARKS
Best way to view an
impression…
Making a cast!!!!
For example, a trip to the dentist……
You all have had one of
these done before??
What happens??
An impression is made…. This would be your tire tracks,
foot prints, etc
Then it is filled with a plaster that is mixed up
This is allowed to dry and it pulled out of the impression
THEN YOU END UP WITH…..
YOUR
MOLD/ CAST
TODAYS FOCUS
TIRE TRACKS!!!!!!
Why is tire track evidence so
hard?????
Because there are so many cars that
are similar!!!!
Police have to go in
and find that
specific car that
matches those
tracks, but that’s a
big job to narrow
down.
Tire track evidence consists
of….
Tire track width
Wheelbase dimensions
Turning diameter
Relative positions of
turning tracks
RECOVERY
Tire impressions must be:
Photographed from all angles with and
without measurement tool (ruler)
Cast – a 3 foot impression requires 15-25
pounds of dental stone
Measured – width, length and depth
Direction of travel noted
Impressions made if possible, and
Pictures of the source (tire) must be
included for comparison
COMPARISONS
Tire tread examinations compare the
tire impressions recovered from scene
with tires taken from a known vehicle
Two categories of tires:
Suspect - Vehicle of suspect
Elimination - Vehicles of police,
ambulance, etc
All tires should be seized from suspect
vehicle for comparison
COMPARISONS
Forensic examination begins with
visual comparison and elimination of
tires which do not match impression
Forensic examination continues with
full circumference test impressions
Impressions are superimposed on
known impression over cast or original
tire
So what did we learn already??
Tire tracks would be considered
what type of evidence???
CLASS!!!!
Tire tracks can be individualized
how????
Wear marks
Nails in tires
Patching
Gravel
Skidding caused by sudden stops
Forensic Science Activity
http://pro.corbis.com/images/CB001940.jpg?size=572&uid={D27A89DF-00BB-4028-AA57-7A908AF0511D}
T. Trimpe 2007 http://sciencespot.net
Tire Track Lab
Your group will need to document the
tread patterns for each vehicle.
Step 1: Get a large piece of white paper from your teacher, an ink pad, paper towels,
and a ruler. You will also need a pen or pencil.
Step 2: Gently roll a car over the ink pad several times to cover all the sides of the
tires.
Step 3: Gently roll the car on the white paper for a length of 5-6” and label the
tracks with the car’s letter.
Caution: You will want to apply enough pressure to get a good impression, but not
too hard that you cause damage to the vehicle, its tires, or the ink pad.
Step 4: Roll the car on a piece of paper towel to remove excess ink and then pass it
along to another group.
Step 5: Analyze the tire tracks to identify unique characteristics, such as blank spots,
evidence of tire wear, width of the track, etc. Use a highlighter to mark each
characteristic you find.
Tire Track Challenge
Work with your investigative team to identify each set of tracks
shown on your worksheet.
Compare the tracks you made earlier and match them to the
suspect tracks on the worksheet. Once you have identified all the
cars, have your answers checked by your teacher.
WARMUP
Why are tire tracks so hard to trace
to a source? What would make them
easier to link to a suspect’s vehicle?
UNIT 3: DAY 2
FOOT PRINTS!!!!!
What are footprints??
Impression left in the Earth after someone walks on
it.
What can footprints tell us
about a crime???
Direction of approach and departure
Point of entry and exit
Mode of entry
Sequence of events that took place
How long can footprints last?
Couple of minutes to hundred of years…..
So what type of evidence can a footprint be??
TRANSIENT!!!!!
Footprints Can Be 2D or 3D
Things Prosecution Looks for
When Examining Footprints
The walk or gait of the person who left the
footprints,
Sole or heel indents
Cuts or the tread of a shoe, and
Other signs of wear associated with a shoe.
Investigators can determine a
person’s size and the speed
(Running or walking) they were
going
Gait
A manner of walking or moving on foot.
It can be as individualized as your
personality.
Three things are needed to
actually use footprints to convict
someone….
A photography, plater mold, or print of the
original and un-tainted footprint,
The actual shoe or mold of a foot that belongs
to the defendant and the prosecution believes
matches the one at the crime scene
An expert witness that can testify to the
connection between the two beyond a
reasonable doubt.
http://www.youtube.com/watch?v=qlmZZoLGMpM
LAB
FOOTPRINT CASTING
MEASUREMENTS
DIRECTIONS
Meaure length of shoe you’re wearing by standing on ruler
Have someone measure your height
Collect similar data from your classmates
Plot height (y axis) against shoe length (x axis). One set for
males, one set for females
Questions to Consider
Is there a correlation between shoe
length and height?
How could investigators utilize this
information?
WARMUP
What steps would a detective take
to determine who a suspect is based
on footprints?
UNIT 3: DAY 3
Tool Marks
What causes tool marks??
The use of a tool against a usually softer
object
Ex: screwdriver used to open a window is
pressed into the softer windowsill, leaving a
mark
How can tools be used in a
crime?
Stabbing or hitting another individual
Break into things
Features to Analyze
• Dimensions of the impression
• Ridges or striation patterns
• Defects, such as nicks and chips
• Paint chips or metal shards left on a tool
Places and Surfaces Where
Tools Might Be Used
wire,
chainsdoor and window
framessections of sheet metal
safety-deposit boxes,
human bone or cartilage
padlocks, doorknobsbolts and locksand a variety of
other materials
Main Tools Used At a Crime
Scene
bolt cutters
screwdrivers and chisels
scissors
knives and box cutters
pliers and wrenches
crowbars tire irons
saws, knives
Read more at Suite101: Toolmarks at a Crime Scene: Forensic Criminal Investigations can Link Toolmarks to Tools | Suite101.com
http://suite101.com/article/toolmarks-at-a-crime-scene-a41620#ixzz27FRzXMQS
Tools Can Be Classified Two
Ways
Impression
Scratches
Class and Individualized
Characteristics
Class- Size and
shape of tool.
IndividualizedAs tool is used
more it becomes
worn and
damaged
Forensic Science Activity
T. Trimpe 2007 http://sciencespot.net
Tool Marks Lab
Goal: Your group will need to examine and document the tool
marks made by each of the tools.
At each station, you will need to:
1 – To prepare for the lab, roll the modeling clay into a flat circle that fits inside the
plastic plate. Make several impressions of each tool in your slab of modeling clay.
2 – Use the ruler to record the measurements for each tool and its impression
surfaces.
3 – Document any unique characteristics you notice on each tool or its impression.
Write your observations on your worksheet.
4 – After you have documents both of the tools at that station, roll the clay into a ball
to prepare for the next group and wait until it's time to rotate to the next station.
Features to analyze:
• Dimensions of the impression
• Ridges or striation patterns
• Defects, such as nicks and chips
• Paint chips or metal shards left on a tool
Image: http://www.maine.gov/dps/msp/criminal_investigation/crimelab/images/toolmarks1.jpg
Tool Mark Challenge
Work with your investigative team to identify the crime scene
tools.
Compare the tool marks you made earlier and match them to the
crime scene tools. Once you have identified all the tools, have your
answers checked by your teacher. Keep trying until you have
them all correct!
WARMUP
How can a tool mark be
individualized?
UNIT 3: DAY 4
BITE MARKS
When are bite marks most often found??
Assault or sexual attack
Victims of domestic violence
EVERYBODY HAS
DIFFERENT TEETH
SHAPES
WIDTH
ARRANGEMENT
What Else Can Differentiate
Teeth?
Chips
Fillings
Crowns
Caps
Features to Analyze
Type of bite mark (animal or human)
Characteristics of the teeth
Color of the area to estimate how long it’s been
Swab body fluids for DNA
Forensic Odontology
branch of forensic science that
deals with the handling,
examination, and presentation
of dental evidence in court
Why Teeth??
They can
withstand
fire, harsh
conditions,
etc.
X-RAY records
can identify an
individual
involved in a
gruesome
murder where
body is no longer
recognizable
Wayne Boden: “The
Vampire Rapist”
Bite Marks Were One Main
Piece of Evidence Used to
Convict Ted Bundy
http://www.youtube.com/watch?v=HxQ1QFUGKqo
Presentation developed by T. Trimpe 2010 http://sciencespot.net
Part 1: Make an Impression
1 – Fold the Styrofoam plate in half.
Maxilla
2 – Label one side MAXILLA and the other MANDIBLE.
Mandible
3 – Gently bite down on the plate to leave your bite mark
impression.
Maxilla
4 – Place a sheet of the plastic film over the impression and
use a permanent marker to recreate the pattern to match
that of your bite mark.
5 – Use a ruler to make the measurements shown and
record in the table below along with any notes regarding
unique characteristics you observe in the teeth.
http://forensicfact.files.wordpress.com/2008/05/cast_negative_resized_copy.jpg
Mandible
Width
Depth
Part 2: Tasty Testing
1 – Use the various pieces of candy to make bite mark impressions.
2 – Record your observations for each one as well as provide a rating of the
impression quality using poor, fair, or good.
Type of Candy
Quality
Observations
WARMUP
What did you learn from the bite
mark activity yesterday?