Basics of Footwear/Tire Tracks Impressions March 5, 2015

Transcription

1 Basics of Footwear/Tire Tracks Impressions March 5, 2015

2 Sirchie Training Footwear Impression 1 Detection, Recovery, & Identification July Footwear Impression 2 Examination, Comparison, & Identification April or October Evidence Collection Accelerated Training March 9-13, April 13-17, May 11-15, June 8-12, September 14-18, October 12-16, November

3 Today s Agenda Background and Overview Footwear Impression Processing Methods Casting Demonstration Q&A

4 Background and Overview Why is This Type of Evidence Important? Footwear and Impression Evidence can help determine: Whether or not a suspect was at the scene Paths of entry and exit Involvement of the evidence Events that occurred during the crime Type, make, description, and approximate size Number of suspects And more

5 Background and Overview Why is It Often Overlooked? The crime scene must be preserved & footwear evidence needs to be one of the first considerations Evidence can be easily eradicated by weather or by people and vehicles

6 Background and Overview How Should You Search? Once the scene is secure, take measures to make sure you are not disturbing the potential evidence Indoors, darken the area and use a strong white light with a directional beam cast at an oblique angle Once you find evidence, photograph and document Position of the evidence and its surrounding areas

7 Background and Overview Four Basic Methods of Recording Footwear Impressions at the Crime Scene Photography Documentation/Sketching Casting Lifting

8 Categories of Impression Evidence Latent impression not visible to the naked eye Patent impression visible Negative impression - results from the removal of a substance from a substrate by a shoe or tire Residue impression - deposition of a substance from the footwear or tire onto another surface Three-dimensional impression impression made in surfaces with dimensions of length, width, and depth Transfer impression - acquiring residue (mud, blood, etc.) that the footwear or tire subsequently deposits or transfers to a substrate in the form of an impression

9 Footwear Impression Processing Methods Electrostatic Dust Lifter Powder Regular Powder Magnetic Powder Gelatin Lifters Fingerprint Tapes Bloodstain Enhancement Leuco-Crystal Violet Amido Black Ninhydrin for Footwear Casting

10 Tips for Photographing Impressions Always photograph and sketch/document evidence before casting or lifting Take an overall, medium, and close up Always use an L-scale Always make sure camera is at a 90 degree angle to the impression (typically use a tripod)

11 Tips for Photographing Impressions Take photos with light from various angles to capture detail Use oblique light to show contrast (requires cover outdoors) Use compass and directional arrow to orient the impression in location When tracking footprints or tire tracks, should place identifying placards in sequential order (numbers or letters) next to each impression Photograph the scene with all the numbers in it to help relate impressions

12 Photographing Impressions Photographs courtesy of Dwane Hilderbrand, Forensic ITC Services

13 Why Cast Impressions? 3 dimensional Cast gives a lifelike and actual-size molding of the original impression including uneven surfaces and depths Cast gives reproduction of randomly acquired characteristics In deep impressions, the cast gives reproduction of characteristics of the side of outsoles and midsoles of the shoe which usually are not reproduced in photographs Focus or scale problems are eliminated Backs up photographs

14 Types of Casting Material Silicone Expensive, Can flow into hairline cracks and crevices, Difficult to clean from impression without release agent Plaster of Paris Inexpensive, Low tensile strength (breaks easily), Subject to expansion, shrinkage, & image distortion, difficult to clean debris from without damage Dental Stone Medium to High tensile strength (type dependent), easiest to clean, virtually expansion and distortion free

15 Casting Scenarios Soil or Sand Standard casting procedure May require soil conditioner Snow Use coating material for contrast / pre-form Sulfur casting Water Powder dental stone to begin, premixed on top

16 General Casting Method Place a form around the impression to be cast Remove any large objects that are not imbedded in the impression (sticks, stones) Use appropriate preparation (Dust and Dirt Hardener or Snow Impression Wax) Mix casting material according to directions You may pour mixture onto a spoon or stirring stick when dealing with very loose soil Start outside the impression and work in Aim casting material into itself, allowing flow to push material and cover impression

17 Post casting Allow cast to set before removing (generally 1-2 hours depending on conditions) Do not attempt to clean or examine the cast for at least 24 hours Once set, clean with a bristle brush

18 Demonstration Video Please note: our training videos are hosted on Youtube. We know that a few departments block streaming video and ask you to please come back after this 14 minute video is done for the live Question and Answer period. Thank you for your patience and understanding.

19 Thank You & Questions Dyer Bennett and Jim Gocke Phone (800) or Visit Question & Answer

20 Types of Sirchie Casting Materials Shake-n-Cast Dental Stone Plaster Liquid Silicone Toolmark Casting

21 Sirchie Training Footwear Impression 1 Detection, Recovery, & Identification July Footwear Impression 2 Examination, Comparison, & Identification April or October Evidence Collection Accelerated Training March 9-13, April 13-17, May 11-15, June 8-12, September 14-18, October 12-16, November