Forensic Science - 07 Casts and impressions

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A closer look at how casts and impressions are used by forensic scientists in a criminal investigation.

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Forensic Science - 07 Casts and impressions

  1. 1. DRYSDALE CSI Casts and impressions. Ian Anderson Saint Ignatius College Geelong
  2. 2. TYPES OF IMPRESSIONS.  Three basic categories:  Patent impressions.  Latent impressions.  Plastic impressions. Source: Bertino & Bertino, 2012
  3. 3. TYPES OF IMPRESSIONS.  Patent impressions.  Two-dimensional impressions.  Visible.  Produced when material (such as soil, dust, paint, blood, etc.) is transferred from an object (e.g. the sole of a shoe, tread of a tyre, etc.) and deposited onto a hard flat surface. Source: Bertino & Bertino, 2012
  4. 4. TYPES OF IMPRESSIONS.  Latent impressions.  Two-dimensional impressions.  Invisible to the naked eye, but can be made visible by dusting and electrostatic techniques or chemicals.  Produced when minute debris (such as oil, fine soil, etc.) is transferred from an object (the sole of a shoe) and deposited onto a clean floor. Source: Bertino & Bertino, 2012
  5. 5. TYPES OF IMPRESSIONS.  Plastic impressions.  Three-dimensional imprints.  Visible.  Produced when an object (e.g. the sole of a shoe, tread of a tyre, etc.) is pressed into soft, plastic material such as mud, sand or snow. Source: Bertino & Bertino, 2012
  6. 6. IMPRESSIONS. Are impressions individual or class evidence?  Depending on how they are made, impression evidence can be classed as either individual or class evidence.  Class evidence:  Tread pattern of shoes or tyres may identify a brand and size, but it will not identify a specific person or tyre. Source: http://www.criminaljusticeschoolinfo.com/impression- evidence.html
  7. 7. IMPRESSIONS. Are impressions individual or class evidence?  Depending on how they are made, impression evidence can be classed as either individual or class evidence.  Individual evidence:  Distinguishing characteristics on the impression, such as defects or unusual wear, can be used to identify a specific person or tyre. Source: http://www.fbi.gov/about-us/lab/forensic-science- communications/fsc/july2009/review/2009_07_review02.htm
  8. 8. SHOE IMPRESSIONS.  Much information can be obtained from a shoe impression, including:  Size of shoe imprint  size of a person’s foot.  Depth of shoe or foot imprint  person’s weight.  Type of shoe (e.g. work boot v flat dress shoe)  information on the person’s job or personality.  Brand of shoe  information about the buyer. Source: http://thestylesketcher.blogspot.com.au/2011/04/back-to- drawing-board.html
  9. 9. SHOE IMPRESSIONS.  Shoe wear patterns.  Wear patterns on a shoe are different from person to person.  Even on the same type of shoe!  Factors that personalize a shoe pattern includes:  Body weight.  Shape of the foot.  Whether the person walks with their toes pointing straight ahead or pointing in or out.  The wearer’s activities. Source: Bertino & Bertino, 2012
  10. 10. SHOE IMPRESSIONS.  Gait and tracks.  A person’s walking habits (gait) can be determined by examining numerous prints together.  e.g. A limp will result in an asymmetrical gait.  The tracks can indicate whether a person is walking or running.  Based on length of stride and the pressure and shape of the impression. Source: http://www.forensicsreport.com/research/A_formula_that_can_calcul ate_a_persons_speed_by_just_looking_at_their_footprints.asp
  11. 11. COLLECTION OF SHOE IMPRESSION EVIDENCE. 1. Photograph impressions. Source: Bertino & Bertino, 2012
  12. 12. COLLECTION OF SHOE IMPRESSION EVIDENCE. 1. Photograph impressions. 2. Lifting latent impressions.  Using a range of methods including:  Luminol – for bloody footprints.  Dusting.  Electrostatic lifting. Source: Bertino & Bertino, 2012
  13. 13. COLLECTION OF SHOE IMPRESSION EVIDENCE. 1. Photograph impressions. 2. Lifting latent impressions.  Using a range of methods including:  Luminol – for bloody footprints.  Dusting.  Electrostatic lifting. 3. Casting plastic impressions.  A cast can be made of a three-dimensional shoeprint.  Exact method depends on conditions at the crime scence.  e.g. on sand:  Hair spray is sprayed onto impression.  Plaster of Paris is poured into impression.
  14. 14. COMPARISON OF SHOE SIZE V HEIGHT.  A person’s height is usually related to a their shoe size.  The shoe model must first be identified before the shoe size of an impression can be determined.  A running shoe Size 9 will be shorter in length than a work shoe Size 9. Source: http://cantorsappsychologyblog.blogspot.com.au/2011/09/blog-comment-3- correlation-project-hair.html
  15. 15. TYRE TREADS AND IMPRESSIONS.  Tyre marks may indicate the speed a car travelled when it skidded off the road, or the direction it travelled as it accelerated from the crime scene.  Motor vehicles can leave patent, latent or plastic tyre patterns. Source: http://www.dailymail.co.uk/news/article-2247011/Jerry-Brown-alive- shouting-help-accident-drunk-Josh-Brent-did-witnesses-claim.html
  16. 16. TYRE TREADS AND IMPRESSIONS.  Tyre tread and impressions are examined for two characteristics at a crime scene:  Tread pattern & measurements.  To identify the type of tyre and perhaps make & model of the car.  Tyre tread impressions  tyre brand.  Track width, wheel base & turning circle  make & model of car.  Nature of the impression.  To determine how the vehicle was driven. Source: http://www.resolvematters.ca/index.php?pid=7&ref=1037
  17. 17. DENTAL PATTERNS IN FORENSICS. The individual pattern of teeth can be used in two ways. 1. Dental remains can be used to identify an individual.  Teeth are compared against available dental records. 2. Bite patterns can be used to identify a suspect.  Reliability depends on the number of points of comparison and the clarity of the impression. Source: Bertino & Bertino, 2012
  18. 18. CASE STUDY. Ted Bundy (1978). A man wearing a stocking cap entered a Florida State University sorority house and attacked some of the women inside. Two women were killed and two more seriously injured. One of the women had a bite mark that was photographed as evidence. Subsequent attacks followed in other states. Source: http://www.telegraph.co.uk/news/worldnews/northameric a/usa/8678555/Blood-of-serial-killer-Ted-Bundy- discovered-by-police.html
  19. 19. CASE STUDY. Ted Bundy was charged with the Florida State University attacks after his dental impressions were compared to those left on a victim. The FBI’s Behavioral Science Unit had profiled Bundy as a very neat, organized, serial killer. Bundy was so meticulous that he never left fingerprints even in his own apartment. Bundy escaped from police twice, only to be recaptured. Bundy was found guilty of murder and was executed in 1989. Before his execution, he implied having committed approximately 50 murders! Source: http://anilaggrawal.com/ij/vol_005_no_002/reviews/tb/pa ge008ex.html
  20. 20. http://sick9CSI.wikispaces.com/

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