Lecture: Physical Evidence - Classification and Identification

Characteristics of evidence Class characteristics Individual characteristics  features that place the item into a specific category  features that distinguish one item from another of the same type

Types of physical evidence BODY FLUIDS ÙConventional serology: òpresence of blood in stains òspecies identification and ABO grouping  is not adequately informative to positive identify a person ÙDNA analysis can associate victim and/or suspect with each other or with the crime scene BLOODSTAIN PATTERNS òadditional information SEM: erythrocytes & lymphocytes

Types of physical evidence BODY TISSUES  organ samples collected at autopsy, including blood, urine and stomach contents DRUGS & CONTROLLED SUBSTANCES  plant materials, powders, tablets, capsules òtoxicological analysis òvolatile compounds (ethanol, methanol, isopropanol) òheavy metals (arsenic) ònonvolatile organic compounds (drugs of abuse, pharmaceuticals)  miscellaneous (strychnine, cyanide) òtrace drug presence, identity, and quantity òBlack tar heroine wrapped in cellophane

Types of physical evidence DOCUMENTS Ùexamination òtyped, handwritten and printed materials for evidence of forgery  indented writings, obliterated or altered writings, used carbon paper, burned or charred paper Ùpaper and ink analysis Ùhandwriting comparison to determine authenticity Obliterated writing examination

Types of physical evidence HAIRS Ùhairs analysis can determine Ùmorphological features ÙDNA analysis  toxicological examination  FIBERS òhuman/animal òrace òbody area òcosmetic treatments òmethod of removal (crushed, cut, burned, forcibly removed, fallen out naturally) òcan associate a hair to a person òpositive identification  presence of drugs and poisons òtype òcolor, composition construction

Types of physical evidence Two matching hairs identified with the comparison microscope Flax fibers viewed with polarized light

Types of physical evidence FINGERPRINTS òthe strongest possible evidence of a person’s identity FIRE DEBRIS & EXPLOSIVES RESIDUE EXAMINATIONS òidentification of accelerants and explosive residues Fingerprint Matching Unburned accelerator liquid on a soot covered carpet

Types of physical evidence FIREARMS & AMMUNITION Ùindividual microscopic marks òidentification, source, operability of firearms. Ùdetection and characterization of gunpowder residues Ùmuzzle-to-garments distance estimation GLASS FRAGMENTS òCause of breakage òDirection of breakage force òPhysical fitting òGlass fragment comparisons Photomicrograph: test bullet - questioned bullet Glass fracture produced by a high-speed projectile

Types of physical evidence PAINT & PAINT PRODUCTS Ùanalysis and comparison of paint transferred from the surface of an object to another during the commission of a crime: òSuspect vehicle impacting a victim vehicle; a pedestrian or a stationary object òTool impacting stationary object ÙPaint databases can help identify the year, make and/or color of a motor vehicle from a chip of paint left at the scene. Paint Layers on Wood Surface

Types of physical evidence TOOLMARK IDENTIFICATION òmicroscopic side-by-side comparison òattempts to link a particular tool with a particular mark to the exclusion of any other tool ROPE & CORDAGE  composition, construction, color and diameter Spacing between teeth in gripping -major role in toolmark examinations òmanufacturer

Types of physical evidence SOILS & MINERALS òcomparison between two or more soils to determine if they share a common origin òcolor, texture, composition comparison WOOD òplace the suspect at the crime scene  side or end matching, fracture matching and species identification. Cross-section - Xylem Layers of soil exposed at a grave site. Each layer must be sampled

Types of physical evidence OILS/GREASE & COSMETIC PRODUCTS SHOEPRINTS & TIRE TREAD IMPRESSIONS òhave value for forensic comparisons. òcan provide positive identification of the suspect’s shoes or tires from the suspect’s vehicle. òpossess unique composition for comparison Shoeprint collected using a gelatin lifter.

Processing physical evidence discovering, recognizing and examining it; collecting, recording and identifying it; packaging, conveying and storing it; exhibiting it in court; disposing of it when the case is closed.