lecture 18 19 impression evidence n.
Skip this Video
Loading SlideShow in 5 Seconds..
Lecture 18-19 Impression Evidence PowerPoint Presentation
Download Presentation
Lecture 18-19 Impression Evidence

Loading in 2 Seconds...

play fullscreen
1 / 65

Lecture 18-19 Impression Evidence - PowerPoint PPT Presentation

Download Presentation
Lecture 18-19 Impression Evidence
An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

  1. Lecture 18-19 Impression Evidence Enhancing Footwear Impressions

  2. Chemical Enhancements of 2D Impressions • Dry Residue Prints • Dust or Dirt? • 8-hydroxyquinoline • Fluorescent reaction with iron, aluminum and magnesium. • Spraying the reagent in the dark (outside this is difficult) gives yellow-white fluorescence that must be photographed immediately. • Testing the background before spraying the impression is critical • Testing a small part of the impression to see if the reagent is going to react with the dust/dirt present. 8-Hydroxyquinoline – UV Light

  3. Chemical Enhancements of 2D Impressions Bromophenol Blue and BromocresolGreen Chemical Reagents Before Enhancement After Enhancement After Water Vapor Treatment Journal of Forensic Sciences, JFSCA, Vol. 41, No. 1, January 1996, pp. 23-26.

  4. Oil or Fats • Iodine fuming • Iodine fuming followed by development with 7,8-benzophenone gives a blue/purple color. • First test a small part of impression and surface to see if the iodine is reacting. • Not a chemical reaction that takes place but more of an incorporation of the iodine into the matrix of the oil/fat. • Another way to visualize an iodine infused impression is to dust it with cornstarch and then hold a steam iron over the impression. The iodine will react with the starch to form a dark blue color. • Salt • In the winter, tires running over roads salted with NaCl (sodium chloride) will have the salt on the tread. • Transferred to a surface over which the vehicle travels. Spraying the impression with Silver Nitrate (AgNO3) will form silver chloride (AgCl) in those areas of the impression containing sodium chloride. • Shining a UV light or allowing sunlight to bake the impression will convert the AgCl to metallic Silver (Ago), which will appear dark gray or black.

  5. Using Photography to Enhance • Photographic sequence important • Establishing ( • Midrange • Close-ups (examination quality or 1:1) • Record detail • With & without scale – In the same plane • Need to make 1:1 enlargements • Next to & parallel to print @ same level as impression • Made in plane of impression (vertical to impression) • Tripod is essential • Appropriate lighting • Oblique • ALS • RUVIS Camera Setup http://site.utah.gov/dps/impressions-fw-evidencecollection_000.htm

  6. Photographing Footwear Impression Evidence • Examination quality photographs should always be taken of both two-dimensional and three-dimensional footwear impressions • Photographs are taken for later comparison with known footwear • A PROPER scale should ALWAYS be used when photographing footwear impressions • The scale should be on the same plane as the impression • Objects with impressions should be removed from the scene if possible, AFTER examination quality photograph taken • Always use a tri-pod • Fill the frame of photograph with your impression including your scale • Shade impression in sunny conditions • Use side lighting from different angles • take several shots

  7. Proper Location of Light Source for 2-D Residue Prints Light Source Should Be 4-5 Feet From Impression From: Bodziak: Footwear Impression Evidence1

  8. Existing Overhead Lighting Oblique Lighting 10 Degrees Oblique Lighting 25Degrees Oblique Lighting 45 Degrees Ambient Light + External Source From: Bodziak: Footwear Impression Evidence

  9. Oblique lighting Flashlight Electronic Flash

  10. Cross Polarization – Can Cut Glare High-Contrast B/W Photography • Film cameras • High-contrast B&W film • Kodak Tech Pan • Digital Cameras • Use B&W setting • Use software to convert color images • Filters • Subtract out the background • Gray impression on red floor • Use red filter on camera • Use UV or IR light • ALS • Polarizing filters can enable impressions to be photographed • One filter in front of oblique light source • Other filter in front of camera lens • Rotate filters to achieve max visibility of impression • Important technique for cutting glare

  11. UV Light • UV wavelengths • UV spectrum : 10-400nm • Long-wave: 320-400 • Middle-range: 280-320 • Below 200: not useful • Use Reflected short-wave UV light - RUVIS • 18A filter over lens of camera • Filters out visible entering camera but not UV light Unaided Eye Long Wavelength UV Image http://www.ultravioletcameras.com/pdf/ETM-LongwaveUV.pdf (Photos Rachel Leintz)

  12. IR Light • IR Spectrum • Useful portion: 700-900nm • Digital Camera altered for IR • Use tungsten light source - strong IR light • Use #87 filter over camera lens to block all visible light

  13. Enhancement of Bloody Footwear Impressions - Photography Using the ALS & Chemically Bloody Print On Terracotta Tile Photograph With Flashlight Bloody Footprint Developed with Amido Black Protein Stain Some blood enhancement chemicals work on only non-pourous surfaces (amido black), pourous surfaces (hungarian red), and some will work on both pourous and non-pourous (LCV). Once impression photographed, it can be collected.  This can be done by submitting the entire piece it was left on, or a gel lift can be used. Photograph using ALS @ 535nm http://site.utah.gov/dps/impressions-fw-evidencecollection_000.htm

  14. UV Light (Photos courtesy of Stephen Warlen, Kansas City (Missouri) Police Department http://www.ultravioletcameras.com/pdf/ETM- LongwaveUV.pdf

  15. Choosing a Method for EnhancingLots of Choices • Need to understand the surface , • How the method works • Method’s limitations

  16. Lifting 2D Impressions BVDA Gellifter Storage Box http://www.evidentcrimescene.com/cata/cast/cast.html

  17. Lifting 2D Prints Electrostatic Lifts

  18. Preserving Electrostatic (and Gellifter) Lifts High Quality Cardboard Box Tape Lift to bottom of box Gellifter Lifts: Do not cover lifts with clear acetate cover http://site.utah.gov/dps/impressions-fw-evidencecollection_000.htm

  19. Wet Residue Prints • Made from wet shoes/boots • Enhancing depends on • Chemistry of recipient surface • Chemistry of the impression • Preservation technique

  20. Powder Dusting Wet Residue Footwear Impression Fingerprint powder (magnetic powder), can be used for collecting footwear evidence of WET ORIGIN.  A wet origin impression is made when a wet shoe with dirt and debris walks across a solid surface such as tile or a wood floor.  After drying, the dried impression is left. Use oblique lighting to find impressions. http://site.utah.gov/dps/impressions-fw-evidencecollection_000.htm

  21. Lifting Dusted Impression With White Gellifter http://site.utah.gov/dps/impressions-fw-evidencecollection_000.htm

  22. Chemical Methods • Because of soil components, we can enhance • footwear Impressions chemically. • Best and most logical approach • Employ Chemistry in the laboratory instead of at scene. • However, some scene circumstances may dictate chemical enhancement @ scene. • The result is either a colored or fluorescent impression, which can be photographed easily.

  23. Enhancing Wet Residue Prints

  24. Chemical Checklist • Checklist: Choosing method depends on following: • Chemistry of the recipient surface. • Chemistry of the impression • Preservation technique • The chemistry of the surface critical to successful enhancement. • If impression lies on a linoleum floor and the only resource is 8-hydroxyquinoline, always the possibility that the surface will react with the reagent • Will mask the fluorescence of the impression. • Check chemistry of the surface first - ensure that it does not react with reagent. • The chemistry of the impression also critical • Before treating impression determine whether the components in the impression are going to react with the reagent and give the expected color or fluorescence.

  25. Preserving 2D Wet Residue Prints • Print dusted with magnetic powder • Gel Lifted with White Gellifter • Alternative techniques • Powder Suspension (WetWop – Iron Oxide) • Iodine + benzophenone • Iodine/starch • Magnetic Powder

  26. Packaging 2D Impressions • Place lift side up in appropriate box • Tape to bottom • Cover electrostatic lift with silicone lift paper & • Leave gellifter lift uncovered • Place into high quality cardboard box • Think better quality pizza box • High quality cardboard box http://site.utah.gov/dps/impressions-fw-evidencecollection_000.htm

  27. Bloody Footwear Impressions OJ Simpson Murder Case - 1994 http://www.members.tripod.com/~VanessaWest/nsimpson2.jpg

  28. 3D Impressions

  29. 3-D Impressions Impressed Evidence • Typically found in exterior surfaces • Shoe deforms surface • Sand/soil/snow – other soft surfacesCharacteristics • Vary widely • Shallow or deep • Quality varies • Can have great detail or none

  30. 3-D ImpressionsValue of 3D Impressions • Impressions with sufficient detail can be associated with a specific item of footwear • Impressions in clay-based soil • Can retain great detail • Impressions in sand & small rocks • Little detail • Dry packed snow • Greater detail than wet, melting snow

  31. Collecting 3D Impression Evidence Sequence • Documentation • Sketching • Give lab knowledge where occurred @ scene • Lab can recreate as closely as possible to original • Differences in how recreated in lab v scene can affect making proper match • Field notes • Photography • Necessary for court presentation • Casting • Lifting

  32. Collecting 3D Impression Evidence Sequence • Most impression evidence has 3D characteristics … surface topography. • For forensic purposes, 3D impressions have depth in addition to length and width and commonly found outdoors in a soft or malleable receiving surface such as soil, sand or snow. • The quality (detail) varies with, • The receiving surface’s malleability, texture and composition. • The detail present in the source origin. • The mode by which the impression was transferred to the surface. • The affects of weather: temperature, rain and snow.

  33. Collecting 3D Impression Evidence Sequence • The scene investigator has no control over how the impression was generated or its clarity. • Responsibility: capture detail as completely and as clearly as possible. • Two activities: 1. Photography and 2. Casting. • Casting defined: • “the filling of a three-dimensional footwear impression with a material that will acquire and retain the characteristics that were left in that impression by the footwear.” • Each archiving technique complements the other • Photography and casting are not an either or decision. Both are critical and both must be done in order to properly archive the impressions.

  34. Lifting & Preserving 3D Footwear Impression Evidence

  35. What to Cast Indented (Impressed) Dry Impressions Wet, 2D Prints on Concrete Impressions in Snow Impressions Covered by Water

  36. Photography -v- Casting

  37. Casting Footwear ImpressionsCharacteristics of Forensic Quality Casting Material • Produce very fine detail • Flow easily into impression • Cleaned without loss of detail • Easily obtained with consistent quality & properties • Easily mixed – not require special equipment • Set in reasonable time • Unlimited shelf life

  38. Quality of Casts • Receiving surface malleability, • texture & composition • Sand • Clay • Loamy soil • Detail present in the impression • Mode by which impression transferred to the surface • Mechanics of making the impression • Effects of weather: • Temperature • Rain/snow • Wind

  39. Casting Gypsum manufacturing processes CaSO4-2H2O 110-130 Deg C Gypsum Calcium Sulfate Dihydrate (CaSO4)2-H2O 130-200 Deg C Plaster Calcium Sulfate Beta-hemihydrate CaSO4 200-1000 Deg C Stone Calcium Sulfate Alpha-hemihydrate Open Oven Autoclave Pressure Steam Plaster of Paris Requires more water Irregular Crystals & Porous Consistency > 50 Dental Stone Requires less water Uniform Crystals Dense Crystals Consistency < 50

  40. Choosing Dental Stone Several kinds of dental stone … always check the compression strength measured in psi (pounds per square inch).

  41. Casting Footwear ImpressionsGypsum Consistency vs Compressive Strength (psi) W:P – The quantity of water (by wt.) per quantity of powder (by wt.) A “30 Consistency” means – 30 parts of water/100 parts powder Higher the consistency – longer setting times – lower strength - softer

  42. Mixing Merlin's Magic • Merlin's Magic: Special type of casting material. • Made to pour into molds easily with very few air bubbles. • Mix differently than for regular plaster. Below are instructions to mix up enough plaster to fill one regular size mold. First you need to make a measuring cup that can be reused. http://www.hirstarts.com/casting/dental.html

  43. Procedure for Merlin’s Magic • Need two disposable plastic cups -nested. • Pour 2 ounces (60 ml) of water into the top cup and place a black mark on the outside of the bottom cup where the water line is. • Place an additional 2.5 ounces of water into the cup (for a total of 4.5 ounces or 135 ml). • Place another black mark on the outer cup at the water line. • Remove the inner cup and you have a reusable measuring cup. Here is how you mix the plaster

  44. Insert a new cup into your measuring cup. • Pour in water until it reaches the first line. • Carefully shake in the powder until the mixture reaches the second line. The powder must be absorbed into the water before you can determine if the second line is reached. • Remove the inner cup, mix up the plaster and pour it into your mold. • Mixing by weight, • Use table @ right. Need scale to measure the weight of the powder. • "ounces" shown here are a liquid measurement (not weight). • Mixing instructions on the package of Merlin's Magic will be different. • Their instructions are used for dental castings, which use a vibrator to shake thicker plaster into their dental molds, which can give mix that is too thick to pour into a mold.

  45. Casting Using Dental Stone

  46. Photographing the Impression Proper positioning of scales Positioning of Retainer

  47. Placing the casting frame in place Mixing water (3/4 cup/lb stone) and dental stone Pouring mixture onto impression

  48. Curing the cast Allow to sit 30-40 minutes before lifting Do not remove adhering soil • Final cast • Allow to cure up 24-48 hours • Carefully remove soil • Save Soil for comparisons

  49. CastingUnderwater Impressions • Drain or remove excess water – Good – BUT - Not Necessary • Pipette or syringe • Carefully Absorb with paper towel • Pour casting material as usual • If water can’t be removed? • Frame the impression • Sift dry casting powder gently into water above impression • Allow to fall to bottom • Sift until 1” of powder covers the area • Powder builds up & saturated with powder • Use additional dental stone slurry to fill the framed area • Will settle into the water later & into impression – cover entire impression • Allow to set for at least 1 hour