Xã hội học - Physical evidence

If blood at the crime scene is fresh and relatively uncontaminated, identification is not difficult If the conditions at a crime scene are otherwise it is more difficult to identify One preliminary field test involves the use of Hemident Blood analyses is important because of the value of DNA typing

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THREEPhysical EvidenceLEARNING OBJECTIVESDistinguish between class and individual characteristics.Outline procedures for locating and handling soil and pollen evidence.Understand processes for preserving footwear and tire prints and impressions.Summarize techniques for collecting glass and paint evidence.Discuss methods of collecting and storing fibers, cloth fragments, and impressions.Understand how to locate, identify, and use tools to obtain fingerprints.Describe the importance of forensic dentistry.Discuss the identification and analysis of bloodstains.Identify the determinations that can be made from firearm evidence.Outline techniques for identifying questioned documents.3-1THE CRIME SCENEDefines the location at which an offense was committedSearch the crime scene for physical evidenceIncludes a wider area that contains the lines of approach and,Flight by the perpetratorThe crime scene includes setting of the crime and its general environs3-2CLASS AND INDIVIDUAL CHARACTERISTIC EVIDENCEClass: a group of objects or persons with characteristic physical evidence common to itExamples include soil and hairIndividual characteristics can be identified as having originated with a particular person or sourceEstablishes individualityExamples include fingerprints and footprints3-3LOCATING AND HANDLING SOIL EVIDENCE Soil evidence is important when the suspect drives/walks on unpaved areasIt is picked up by:tire treads shoe bottoms pants cuffs It may also be located in: subject's vehicle articles in a suspect's trunk3-4PRESERVING FOOTWEAR AND TIRE PRINTS AND IMPRESSIONSFootwear prints and impressions should be photographed: As part of the general sceneAlso photograph with a scaleDental Stone is used in casting impressions3-5FOOTWEAR IMPRESSIONSPhotographs of footwear impressions at a crime sceneIn the first photo only the impressions are shownIn a subsequent photo a ruler will be added to show sizesLater casts will be made of the impressions3-6(Courtesy Tampa, Florida, Police Department)COLLECTING GLASS AND PAINT EVIDENCEPaint may be collected from the suspect's tools or clothing.Paint can often be collected in dried chips.Glass is a common form of evidence at burglary scenes.Before any glass fragments are removed from a glass window it should be photographed.3-7COLLECTING AND STORING FIBERS, CLOTH FRAGMENTS, AND IMPRESSIONS Fibers are of greater value as evidence than are rootless hairs.Fibers may be located on the body of the victim and/or the suspect.Cloth fragments may be found at the scene of a violent crime.Cloth fragments may also be found at the suspect's point of approach or exit.3-8THREE BROAD CATEGORIES OF LATENT FINGERPRINTSPlastic prints Created when the fingers touch against some material such as puttyContaminated/visible prints Formed when the fingers are contaminated with such things as ink or blood and touch a clean surface Latent/invisible prints Left on a surface from the small amounts of body oil and perspiration that are normally found on friction ridges3-9(a)CONDITIONS AFFECTING THE QUALITY OF LATENT FINGERPRINTS The surface on which the print is depositedThe nature of the material contaminating the fingerprintAny physical or occupational defects of the person making the printHow the object on which the prints appear was handledThe amount of the contamination3-10METHODS OF DEVELOPING LATENT PRINTSTraditional powdersFluorescent PowdersChemicalsCyanoacrylate of superglue fumingVisualization under:LaserAlternative lightUltraviolet illumination3-11LOCATING PRINTSCrime Scene Technician3-12This technician is using powder to develop latent printsTechnicians often wear protective equipmentSeveral points can be seen(Courtesy Nassau County, New York, Police Department)PORTABLE SUPERGLUE FUMING CHAMBERis used to process the inside and the outside of the car.is more efficient for processing larger objects.3-13(Courtesy Sirchie)FORENSIC DENTISTRY Forensic dentistry is a specialty that relates dental evidence to investigationAnalyses of bit marks had played a major role in many casesTeeth marks may be left in food, pencils or other items left at crime scenesBite marks can help eliminate or identify suspects3-14DENTAL COMPARISONDental records are very useful in helping to identify unknown persons who have been the victim of fowl play or who have been reported simply missing.3-15(Courtesy Dr. Richard R. Souviron, D.D.S., ABFO, Chief Forensic Odontologist, Dade County Medical Examiner Department, Miami, Florida)IDENTIFYING AND ANALYZING BLOOD STAINSIf blood at the crime scene is fresh and relatively uncontaminated, identification is not difficultIf the conditions at a crime scene are otherwise it is more difficult to identifyOne preliminary field test involves the use of HemidentBlood analyses is important because of the value of DNA typing3-16SOURCES OF DNA EVIDENCEThese are common sources of blood and DNA evidence that investigators need to be aware of in conducting crime scene searches. 3-17EvidencePossible Location of DNA on the EvidenceSource of DNABaseball bat or similar weaponHat, bandana, or maskEyeglassesFacial tissue or cotton swabDirty laundryToothpickUsed cigaretteStamp or envelopeTape or ligatureBottle, can, or glassUsed condomBlanket, pillow, or sheet“Through and through” bulletBite markFingernail or partial fingernailHandle, endInsideNose or ear pieces, lensSurface areaSurface areaTipsCigarette buttLicked areaInside or outside surfaceSides, mouthpieceInside or outside surfaceSurface areaOutside surfacePerson’s skin or clothingScrapingsSweat, skin, blood, tissueSweat, hair, dandruffSweat, skinMucus, blood, sweat, semen, earwaxBlood, sweat, semen, vomitSalivaSalivaSalivaSkin, sweatSaliva, sweatSemen, vaginal or rectal cellsSweat, hair, semen, urine, saliva, dandruffBlood, tissueSalivaBlood, tissue, sweat(Source: “What Every Law Enforcement Office Should Know about DNA Evidence.” National Commission on the Future of DNA Evidence (Washington, D.C.: National Institute of Justice, 1999), pp.3-4.)3-18HEMIDENTThe use of Hemident in a presumptive or preliminary field test for blood. (Courtesy Lightning Powder Company, Salem, Oregon)DETERMINATION FROM FIREARMS EVIDENCE LAB EXAMINATIONS OF FIREARM EVIDENCE MAY ANSWER THE FOLLOWING QUESTIONSWas this bullet fired from this weapon?What else can be learned from the bullet?What determinations can be made from cartridge cases?What miscellaneous determinations can be made by examination of firearms evidence?3-19BULLET IDENTIFICATIONWhen a bullet passes through the barrel of a weapon distinctive scratches are causedThese scratches can be compared to bullets fired through firearms in questionIdentification is affected by the condition of the gun and of the bullets3-20COUNTERFEIT SOCIAL SECURITY CARDSSocial security numbers are an important source of identification in AmericaCriminals often try to produce social security cards in order to assume new identitiesIllegal aliens also often try to obtain fake social security cards3-21(Courtesy Immigration and Naturalization Service, Forensic Documents Laboratory.)TECHNIQUES FOR IDENTIFYING QUESTIONED DOCUMENTSHandwriting and handprinting examinationsThere are three types of forgery: Traced forgery Simulated forgery Freehand forgery3-22(a)TECHNIQUES FOR IDENTIFYING QUESTIONED DOCUMENTS (cont'd)Photocopier examinationPaper examinationAge of documentsBurned or charred paperAltered or obliterated writingWriting instrumentsmechanical-impression instrumentsTypewriting3-22(b)

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