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WARMUP!!!!!

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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WARMUP!!!!!

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  1. WARMUP!!!!! • When I graduate from high school I want to…….

  2. UNIT 3 IMPRESSION EVIDENCE

  3. What Causes Impression Evidence???? • When one object presses hard against another object and leaves an indentation or print

  4. What kind of impression evidence can you think of?

  5. Tire tracks

  6. Footprints

  7. BITE MARKS

  8. TOOL MARKS

  9. Best way to view an impression… • Making a cast!!!! • For example, a trip to the dentist……

  10. You all have had one of these done before??

  11. 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…..

  12. YOUR MOLD/ CAST

  13. TODAYS FOCUS • TIRE TRACKS!!!!!!

  14. Why is tire track evidence so hard????? • Because there are so many cars that are similar!!!!

  15. Police have to go in and find that specific car that matches those tracks, but that’s a big job to narrow down.

  16. Tire track evidence consists of…. • Tire track width • Wheelbase dimensions • Turning diameter • Relative positions of turning tracks

  17. 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

  18. 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

  19. 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

  20. So what did we learn already?? • Tire tracks would be considered what type of evidence??? • CLASS!!!!

  21. Tire tracks can be individualized how???? • Wear marks • Nails in tires • Patching • Gravel • Skidding caused by sudden stops

  22. Tire Track Challenge Forensic Science Activity http://pro.corbis.com/images/CB001940.jpg?size=572&uid={D27A89DF-00BB-4028-AA57-7A908AF0511D} T. Trimpe 2007 http://sciencespot.net

  23. 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.

  24. 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. Ready? Set? GO!

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

  26. UNIT 3: DAY 2 FOOT PRINTS!!!!!

  27. What are footprints?? • Impression left in the Earth after someone walks on it.

  28. 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

  29. How long can footprints last? • Couple of minutes to hundred of years….. • So what type of evidence can a footprint be?? TRANSIENT!!!!!

  30. Footprints Can Be 2D or 3D

  31. 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.

  32. Investigators can determine a person’s size and the speed (Running or walking) they were going

  33. Gait • A manner of walking or moving on foot. It can be as individualized as your personality.

  34. 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.

  35. http://www.youtube.com/watch?v=qlmZZoLGMpM

  36. LAB • FOOTPRINT CASTING • MEASUREMENTS

  37. 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

  38. Questions to Consider • Is there a correlation between shoe length and height? • How could investigators utilize this information?

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

  40. UNIT 3: DAY 3 Tool Marks

  41. 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

  42. How can tools be used in a crime? • Stabbing or hitting another individual • Break into things

  43. 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

  44. 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

  45. 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

  46. Tools Can Be Classified Two Ways • Impression • Scratches

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