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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.

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  • When I graduate from high school I want to…….



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




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




  • 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


  • 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


  • 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


  • 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

Tire Track Challenge

Forensic Science Activity


T. Trimpe 2007 http://sciencespot.net

Your group will need to document the tread patterns for each vehicle.

Tire Track Lab

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.





  • Why are tire tracks so hard to trace to a source? What would make them easier to link to a suspect’s vehicle?



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??


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


  • 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





  • 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?


  • What steps would a detective take to determine who a suspect is based on footprints?


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,

  • chainsdoorand window

  • framessectionsof 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.comhttp://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.

  • Individualized- As tool is used more it becomes worn and damaged

Tool Mark Challenge

Forensic Science Activity

T. Trimpe 2007 http://sciencespot.net

Goal: Your group will need to examine and document the tool marks made by each of the tools.

Tool Marks Lab

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!

On your mark?

Get set?



  • How can a tool mark be individualized?



  • When are bite marks most often found??

    • Assault or sexual attack

    • Victims of domestic violence





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

Bite Mark


Presentation developed by T. Trimpe 2010 http://sciencespot.net

Part 1: Make an Impression

1 – Fold the Styrofoam plate in half.

2 – Label one side MAXILLA and the other MANDIBLE.

3 – Gently bite down on the plate to leave your bite mark impression.

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.








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.


  • What did you learn from the bite mark activity yesterday?

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