Impression Analysis. Impressions can be individualized for forensic purposes. Types of impressions:...

download Impression Analysis. Impressions can be individualized for forensic purposes. Types of impressions: fabric prints, shoe impressions, tire impressions

of 38

  • date post

  • Category


  • view

  • download


Embed Size (px)

Transcript of Impression Analysis. Impressions can be individualized for forensic purposes. Types of impressions:...

  • Impression Analysis

  • Impression AnalysisImpressions can be individualized for forensic purposes.Types of impressions: fabric prints, shoe impressions, tire impressions & tool marksNo two things are precisely identical & that forensic comparison involves matching features of questioned & unidentified specimen with known standards

  • Impression Analysis Fabric PrintsFabric prints are sometimes encountered by the fingerprint expert in the form of glove impressions.With use, gloves become contaminated with substances such as dirt, grease, oils & even sweat that enable them to leave their imprints, either latent or visible. They may also leave plastic impressions in materials like putty

  • Impression Analysis Fabric PrintsCloth gloves may have snags, tears, or holes that make them distinctive along with imperfections in the weave pattern or other identifiable characteristics.Leather gloves may have wrinkle or crease formations where they do not fit properly or they may exhibit surface cracks, tears or other imperfections or characteristics to individualize them

  • Impression Analysis Fabric PrintsDeveloping glove prints requires special care because they are typically less strong than fingerprints & may be destroyed by use of too much powder.They should first be searched with the aid of a flashlight, laser or other light source & then developed with sparing use of powder.

  • Impression Analysis Fabric PrintsRather than lifting the print, the object on which it is found should, if possible, be taken to the lab for direct comparison with a suspects gloves.Comparison prints from the gloves of a suspect are best made on glass which is generally the most convenient even when the original prints are on furniture.

  • Impression Analysis Fabric PrintsClear prints may be difficult to make, but results may be improved by breathing slightly on the surface of the gloves finger.Other types of fabric impressions may be found at the scene of a crime under certain circumstances such as hit & run accident: fabric impressions from victim may be left in dust on assault vehicles bumper, grille, fender or other area.

  • Impression Analysis Fabric PrintsWhether latent, visible, or plastic, fabric prints should be treated in the manner recommended for glove prints.In photographing them, the camera should be at right angles to the surface to avoid distortionsLifting these prints may be accomplished with sheets of lifting material like that used for fingerprints.

  • Impression Analysis Fabric PrintsNew procedure: portable electrostatic device operating on principle similar to static charge on comb to lift paper; used in recovering faint prints on colored surfacesFabric impressions may show sufficient class characteristics to demonstrate a garment could have made the print or may exhibit individual characteristics from wear/damage so examiner can conclude the garment did leave impression

  • Impression Analysis Shoe & Tire ImpressionsShoe prints & tire prints are left in much the same way as fabric impressions & other types.The shoe or tire becomes contaminated with some substance such as blood, oil, or dust & a latent or visible print is left; alternatively, the print may be a plastic or 3-D one, pressed into mud for example

  • Impression Analysis Shoe & Tire ImpressionsLatent shoe prints are searched for & developed in much the same way as glove & other fabric prints.Whenever impression is made by dust or other powdered material, the procedure is first to photograph it (oblique lighting helpful) & then lift it in manner suggested for fabric prints by using sheets of lifting material or by electrostatic technique.

  • Impression Analysis Shoe & Tire ImpressionsComparison footprints may be made by coating the soles with water-based ink applied from a large ink pad; the shoes are then stepped onto an acetate sheet or a sheet of tracing paper.When the contaminating substance is blood, it may be developed by spraying it with luminol which results in a faintly glowing print observed in darkness

  • Impression Analysis Shoe & Tire ImpressionsWhen either a shoe or tire impression has been left in some moldable substance like clay or snow, its first photographed from directly above to avoid distortion & then cast with plaster of paris or dental stone.With snow imprints, a special Snow Print Wax is used instead. Before plaster or dental stone hardens, identifying information is scratched into the surface

  • Impression Analysis Shoe & Tire ImpressionsFBI maintains a vast file of both shoe (sole & heel) patterns & tire-tread designs for such identificationsExample: O.J. Simpsons size 12 Bruno Magli shoes designer footwear both expensive and rare left bloody shoe prints at crime scene that matched his shoes

  • Impression Analysis Shoe & Tire ImpressionsTire tread impressions are almost as useful as shoe prints. There are thousands of tread designs & every tire wears differently or picks up debris from the road making it unique & identifiable.Each tire on the vehicle can be unique as no two tires wear the same way

  • Impression Analysis Shoe & Tire ImpressionsDimensions may not exactly match due to stretching of imprint from motion, distortion due to pressure, shrinkage by drying of earth or clay or other factors.What is important is that there be discovered points of comparison (various nicks, scratches & other effects of wear) sufficient to effect a match.

  • Impression Analysis Shoe & Tire ImpressionsFor presentation of the evidence at trial, photographs of questioned & known prints are placed side by side with characteristic points marked & numbered rather like the minutiae of fingerprints.

  • Impression Analysis - Tool MarksTool mark examinations may have begun in Europe around turn of century. They became common in US in 1930s following successful use of comparison microscope for matching striations on bullets & firing-pin impression parks on shell casings.Methodology used for firearm examination is fundamentally the same for toolmark comparison

  • Impression Analysis - Tool MarksComparisons made by demonstrating tool mark produced by a given chisel distinct from marks produced by any other chisels.Basis of tool-mark comparisons is that implements used for cutting metal or prying apart objects develop nicks on edges with use & produce pattern of striations during cutting or prying process & is distinctive for a given tool.

  • Impression Analysis - Tool MarksComparison microscope technique similar to bullet comparison is used. Science involved is called comparative micrography.Cutting tools present a special problem since cutting blade is long in comparison to cut region of item involved. Examiner will want to avoid making numerous cuts in order to find the cutting region.

  • Impression Analysis - Tool MarksOne way to accomplish this is to use chemical spot tests to identify traces of cut material on tools blade.To make striation comparisons, tool mark area is placed under one barrel of comparison microscope & the cut or scraped area of test plate is placed under the other.

  • Impression Analysis - Tool MarksThere may be some differences due to bending of metal during cutting or application of uneven pressure or other factorsSome tools may leave an indentation or impression that is similar to a firing pin mark on a shell case. A hammer blow would represent this type of mark as would indentations caused by a pair of pliers

  • Impression Analysis - Tool MarksThe comparison microscope is sued to compare outer shape of impressions as well as surface scratches, nicks, pits or other defects.This is another procedure of comparative micrography. There may even be a combination of marks, both striations & indentations.

  • Impression Analysis - Tool MarksComparative micrography techniques may be employed in matching a piece of broken metal or other material and the piece it was broken from: auto accident.Comparison micrography may reveal tool impressions at a series of burglaries were caused by the same tool, thereby linking the crimes.

  • Impression Analysis - Tool MarksOnce tool marks are discovered, they must be protected until they can be photographed & their locations indicated on the crime-scene sketch.Two photos are required: one showing the mark in its context, the other a close-up photograph to reveal the minute details.

  • Impression Analysis - Tool MarksWhen warranted & practical, structure bearing tool mark is removed. Otherwise, a cast or mold may be made with plasticine or modeling clay.In no event should the investigator place a tool against a tool mark for size evaluations as it may lead to accidental destruction of evidence.

  • Impression Analysis - Tool MarksWhen submitting a tool to the crime lab for examination, actual tool should be used; making of test impression/cuts are functions of qualified technicians.Series of test marks should be made, applying suspected implement of varying angles & pressures to lead plate. It increases likelihood of duplicating details of original mark.

  • Impression Analysis - Tool MarksComparative micrography of tool marks was employed to trace the ladder used in the Lindbergh kidnapping case. This case gave prominence to the science of tool-mark comparisons in much the same way that the St. Valentines Day Massacre did for firearms identification.

  • Case Study: Lindbergh KidnappingNight of March 1, 1932: 9 pm, mother looked in on baby he was sleeping in crib. 50 minutes later, nurse discovered him missing.Co