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Physical Evidence

Physical Evidence

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Physical Evidence

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  1. Physical Evidence Forensics K. Davis Let the evidence speak for itself!

  2. The value of trace (or contact) forensic evidence was first recognized by Edmund Locard in 1910. He was the director of the very first crime laboratory in existence, located in Lyon, France. Remember: Locard’s Exchange Principle "Every Contact Leaves a Trace" The Locard’s Exchange Principle states that "with contact between two items, there will be an exchange." For example, burglars will leave traces of their presence behind and will also take traces with them. They may leave hairs from their body or fibers from their clothing behind and they may take carpet fibers away with them. Source:

  3. Say Something • What is physical evidence? • Why is it important?

  4. Common Types • Blood, semen, and saliva • Documents • Drugs • Explosives • Fibers • Fingerprints • Firearms & ammunitions • Glass • Hair • Impressions • Organs and physiological fluids • Paint • Petroleum products • Plastic bags • Plastic, rubber, and other polymers • Powder residues • Serial numbers • Soil and minerals • Tool marks • Vehicle lights • Wood & other vegetative matter

  5. Significance of Physical Evidence • The examination of physical evidence by a forensic scientist is usually undertaken for identification and comparison. • Identification: The analysis and ultimate identification of a specific physical or chemical substance to the exclusion of all other possible substances or with as near absolute certainty as existing analytical techniques will permit

  6. Identification requires: • Adoption of testing procedures that give characteristic results for specific standard materials • The number and type of tests needed to identify a substance be sufficient to exclude all other substances

  7. The forensic scientist determines what constitutes a thorough and foolproof analytical scheme on an individual basis because simple rules cannot be devised. These conclusions will have to be substantiated beyond any reasonable doubt in a court of law. • Normally used to ID: • Drugs -Explosives • Petroleum products -Blood • Semen -Hair • Species origin (e.g., human blood, rabbit hair)

  8. Comparison • The process of ascertaining whether two or more objects have a common origin. Subjects a suspect specimen and a standard/reference specimen to the same tests and examination to determine if they have the same origin

  9. Comparison (cont.) • Combinations of select properties are chosen from the suspect and the standard/reference specimen for comparison. • Once the examinations are complete, the forensic scientist must render a conclusion with respect to the origins of the specimens. • Probability, or the frequency of occurrence of an event, is the best way to present these results.

  10. Individual Characteristics • Properties of evidence that can be attributed to a common source with an extremely high degree of certainty • Examples • Matching ridge characteristics of 2 fingerprints • Comparisons of handwriting characteristics

  11. Evidence can be categorized as having either individual or class characteristics.

  12. Individual Characteristics • Properties of evidence that can be attributed to a common source with an extremely high degree of probability • Matching ridge characteristics of 2 fingerprints • Comparisons of random striation markings on bullets or tool marks • Comparisons of irregular and random wear patterns in tire or footwear impressions • Comparisons of handwriting characteristics • Fracture matching of broken objects (fitting together like a jigsaw puzzle) • Matching sequentially made plastic bags by striation marks running across the bags

  13. Individual Characteristics • Not possible to have 100% certainty, but rely on probabilities; in these cases, the probability is as high as to defy mathematical calculations or human comprehension. • Example: Probability of 2 individuals having the same fingerprint is one out of 1 x 1060or 1 followed by 60 zeros. Supported by the fact that although millions have been examined over years, there have been no two found alike.

  14. Class Characteristics • Properties of evidence that can only be associated with a group and never with a single source • Comparisons of single layer paint chips • Determining the species of a blood sample • Blood typing • Comparing head light glass • Matching a clothing fiber to various suspect clothes

  15. Class Characteristics • Probability again is a determining factor Ex: Blood types

  16. MIX & MATCH Identification: Comparison: Individual Characteristics: Class Characteristics: • Properties of evidence that can only be associated with a group and never with a single source • The analysis and ultimate identification of a specific physical or chemical substance to the exclusion of all other possible substances • Properties of evidence that can be attributed to a common source with an extremely high degree of probability • Using a standard/reference sample to ascertain whether two or more objects have a common origin.

  17. Product Rule • For blood, we use the product rule to calculate the overall frequency of occurrence of sample in a population. • Product Rule: Multiplying together the frequencies of independently occurring genetic markers to obtain an overall frequency of occurrence for a genetic profile.

  18. Ex. The blood found at the Nicole Brown-Simpson crime scene had a probable occurrence in population of 1 in 200, or 0.44% based on blood typing traits alone. The sample did not match Nicole or Ron Goldman (the victims), thus eliminating them as possible sources of the blood. It did however have many traits in common with OJ Simpson. Ultimately, the scientist narrowed the stain probability down to 1 in 57 billion after DNA testing. In other words, on blood evidence alone, there is only a 1 in 57 billion chance that the sample was not OJ Simpson’s blood.

  19. Current weakness of forensic science is the inability of the examiner to assign exact or even approximate probability values to the comparison of most class physical evidence. • Mainly due to the lack of statistical databases for evaluating the evidence due to mass production of products • How common is a black fiber used in the carpet of the interior of a vehicle used in many makes and models? • The creation of computerized databases for fingerprints, criminal histories, DNA profiles, markings on bullets and cartridges, automotive paints, and shoe marks has helped to strengthen the role of forensic science in criminal investigation.

  20. PROBABILITY AND THE PRODUCT RULE • Physical evidence often lacks individual characteristics that can tie a suspect conclusively to a crime scene. In such cases, prosecutors must rely on evidence with class characteristics to link the suspect to the crime. The likelihood that the suspect and victim are related depends on the number of pieces of evidence linking them and the uniqueness of the evidence.

  21. Which case most strongly suggests the suspect is guilty? • Case 1 Blond hair (32%) Type O blood (43%) Arch fingerprints (5%) • Case 2 Red hair (11%) Type B blood (12%) Loop fingerprints (65%) • Case 3 Brown hair (51%) Type AB blood (3%) Whorl fingerprints (33%) 0.69% 0.86% 0.5%

  22. Most items of physical evidence cannot be linked definitively to a single person or object • Value of class evidence is its ability to provide corroboration of events with data • Only those objects that exhibit a significant amount of diversity in our environment are deemed appropriate for classification as physical evidence. (Ex. A fiber from khaki pants would not be helpful in a case at a school where everyone wore the same type of khaki, uniform pants.)

  23. As the number of different objects linking an individual to crime increases, so does the likelihood of that individuals involvement in that crime • Ex. Wayne Williams: 28 different fibers linked Williams to the murder victims

  24. Physical evidence can serve to exonerate or exclude a person from suspicion, if evidence collected at crime scene differs from controls collected from suspects. • Ex. The standard/reference sample is type A blood, but you have type O blood. This evidence would rule you out as a suspect.

  25. Concerns about physical evidence • Distinguishing between class and individual characteristics • It is difficult to determine the line between class and individual characteristics. (Ex. How many striations need to match on a bullet before it is considered individual?)

  26. Concerns about physical evidence • Distinguishing between evidential variations and natural variations • Testing procedures are so sensitive now that it is difficult to define the limits of natural variation that exists among materials. (Ex. The latest techniques can distinguish glass originating from a single pane of glass.) • This is not always easy. Learning how to use the equipment is not nearly as complicated as gaining the proficiency needed to interpret the observations and data.

  27. Concerns about physical evidence • Determining the weight or significance of physical evidence • The weight or significance of physical evidence is ultimately determined by the jury. • It is important to caution the jury not to approve and admit all “scientific” testimony without first considering its relevancy in a case. • Failure to take proper safeguards may unfairly prejudice a case against the accused.

  28. 3:2:1 • List 3 examples of physical evidence. • Blood, Semen, and Saliva • Fingerprints & Documents • Drugs • Glass, Hairs, & Fibers • Explosives, Firearms, & Ammunitions • List 2 concerns about physical evidence. • Distinguishing between natural variations and evidentual variations. • Determining the weight or significance of physical evidence. • List 1 “rule” we use to determine probabilities. • The Product Rule (multiplying frequencies of individual traits to get an overall frequency)

  29. Types of Analysis • Visual: Evidence that can be utilized or compared through unaided observation (ex. Fingerprints, tool marks) • Microscopic: Evidence that must be observed with the use of some type of microscope (ex. Hairs, fibers) • Chemical: Evidence that must be subjected to any type of chemical procedure to be best utilized (ex. DNA typing, drug screening)

  30. Fracture Matches • • Broken, torn, or cut edges, called fracture lines, that are compared by the naked eye or with microscopes to see if they fit together. • Ex. Tape, glass fragments, paint chips, pieces of a car from an accident, paper bag, etc. • Analysis by Physical Matching • Visible • Microscopic Duct Tape Evidence Images:

  31. Glass • • Glass panes, particles, or fragments that are found or transferred to a person or object involved in a crime that could link a person or object to a particular location. • Ex. glass from breaking and entering, hit and run, vandalism, or murder  CSI Glass Analysis Magnified image of glass fragments Images:,

  32. The pattern of cracks in a windshield fracture can reveal information about speed, occupant position, and angle of impact. Analysis of Glass • Color • Surface Characteristics • Tint • Thickness • Density • Chemical Composition • Refractive Index (RI) • Cause of Breakage • Direction of Penetration (path of projectile) • Order of Penetration (sequence of bullet holes) • Physical Matching (ex. glass from a crime scene to a headlight to a suspect’s car)

  33. Tiny Pieces of Evidence Paint • Any paint, liquid or dried, that may have been transferred from the surface of one object to another during the commission of a crime. • Ex. Transfer of paint from one vehicle to another during an automobile accident, hit-and-runs • Analysis • Microscopic Physical Matching • Paint Layers • Fracture Lines • Chemical Composition • Class Determination: House, Automobile, Nail, etc. • Database: • Make and Model of Vehicle • Brand of Tool • Distributor of Paint Did you know? Most paint evidence submitted to a lab will come from hit-and-run cases involving automobiles.   Did you know? Most paint evidence submitted to a lab comes from hit-&-run cases involving automobiles. Physical Match of Paint Chip Edges Paint Layers Paint Transfer on a Car Images:

  34. Soil, Minerals, Wood, & Other Vegetative Matter • • Any items containing soil, minerals, wood, or other vegetative matter that are found or transferred to a person or object involved in a crime that could link a person or object to a particular location. • Ex. Soil imbedded in shoes or tires, vault insulation found on garments, & rare minerals in soil deposited in the cuff of pants • Analysis • Chemical Composition • Pollen • Plant material • Other Organic Matter Microscopic Image of Sand Images:

  35. Hairs • • Any hairs that are found or transferred to a person or object involved in a crime that could link a person or object to a particular location. • Ex. human or animal hairs (hairs on furniture or clothing) • Analysis • - Microscopic Comparison and Identification • Origin (human or animal) • Stage of Growth (could possibly indicate if the hair was forcefully removed or not) • Match to control hair • - DNA Analysis (if root is present) Microscopic Image of Hairs & Fibers

  36. Fibers • •Any fibers that are found or transferred to a person or object involved in a crime that could link a person or object to a particular location. • Ex. fibers from clothing, carpet, furniture, beds, blankets, etc (carpet fibers on shoes, trunk carpet fibers on body) • Analysis • Microscopic Comparison and Identification • Origin (Synthetic: man-made or Natural: from plants or animals) • Match to control fiber • - Chemical Composition Microscopic Image of Hairs & Fibers

  37. Drugs • Any substance seized in violation of laws regulating the sale, manufacture, distribution, and use of drugs or chemicals • Ex. Cocaine, crack, meth, marijuana, and prescription drugs, etc. • Analysis • - Chemical Composition/ Identification • - Concentration • -  Identifying Components

  38. Human Remains • A body or body parts found at a crime scene. • Ex. A dead body, body parts, wounds on an incapacitated victim • Analysis • Wounds • Physical Matching (weapon type, size, shape, and individual characteristics) • Wound Analysis - to determine extent of injury, characteristics of the suspect (left-handed, right-handed, height, etc.), and positions of the victim and suspect at the time of the incident. Image:

  39. Human Remains Analysis (cont.) • Skeletal Remains • Age, Sex, Race, & Stature (height/build). • DNA Analysis • Bone Fractures and Trauma (clue’s to a person’s past, recent injuries, or the cause of death) • Post Mortem Interval (PMI) and Time of Death • Weather Conditions • Location and condition of body • Insect Life Cycles Source: http://www.crime-scene Images:

  40. Body Fluids & Organs • All suspected blood, organs, and body fluids, human or animal, present in a form to suggest a relations to the offense or persons involved in a crime. • Ex. Blood, semen, saliva, sweat, urine, vomit, body organs, and other physiological fluids and tissues

  41. Body Fluids & Organs Analysis • Detection (Presumptive Testing) • Chemical • Ultraviolet Light • Blood Spatter Analysis • Toxicology (blood, organs, vomit, & urine) • Biochemical Analysis (for identity & origin) • Serological Analysis (for identity & origin) • Blood Typing (blood, sometimes other body fluids if secretors) • Species Determination (human or animal) • DNA Analysis (blood, sperm from semen) • FBI Database: Combined DNA Index System (CODIS) • Became operational in 1998

  42. Firearms, Ammunitions, & Powder Residues • Physical Matching • Rifling: (grooves) in a gun barrel that causes distinctive grooves, indentations, & scratches upon fired bullets, which can be matched to the weapon that fired them • Chemical Analysis • GSR (indicating how close a person was to a fired gun) • National Databases: • Intergrated Ballistics Identification System (IBIS) – ATF Database • Drugfire – FBI Database • National Intergrated Ballistics Network (NIBIN) – facilities exchange of data between IBIS and Drugfire

  43. CSI & Explosives Explosives & Petroleum Products • Any device containing an explosive charge, as well as all objects removed from the scene of an explosion that are suspected to contain the residues of an explosive, including petroleum products removed from a suspect or recovered from a crime scene. • Ex. Explosives: bombs, bombs parts, and residue or traces of explosives found on a suspect’s clothing, skin, hair, or other objects; Petroleum products: gasoline residues, grease and oil stains • Analysis • Chemical Composition (to help ID the type of explosive used and its origin) • Database for fire debris analysis Image:

  44. Latent (prints left at the scene that are not visible to the naked eye) and visible prints that are found or transferred to a person or object involved in a crime that could link a person or object to a particular location. • Ex. Prints could be left on any object: windows, tables, dishes, furniture, etc. • Analysis • Lifting • Matching: type and ridge characteristics • National Database: Integrated Automated Fingerprint Identification System (IAFIS) • Launched in 1999 Fingerprints Images:

  45. Impressions & Tool Marks • Impression evidence is created when two objects come in contact with enough force to cause an "impression." Typically impression evidence is either two-dimensional — such as a fingerprint — or three-dimensional — such as the marks on a bullet caused by the barrel of a firearm. Tool marks are any objects suspected of containing an impression of another object that served as a tool in a crime. • Ex. Impressions: Tire markings, shoe prints, depressions in soft soils, all other forms of tracks, glove and fabric impressions, bite marks; Tool marks: scratches and dents on a locker that was pried open, indentations from a hammer Images:,, &

  46. Impressions & Tool Marks Analysis PhotographedLifted with tape (shoes and tires – 2 dimensional)Cast with plaster (shoes and tires – 3 dimensional)Physical Matching- Indentation Markings (tools)- Wear Patterns (shoes, tires, and bite marks)- Damage (tools, shoes, tires, and bite marks)- Impressions (teeth) matched to dental recordsTraces of blood, fingerprints (tools)Databases- Continuing effort to compile large databases of different types of impressions- Shoes- Tires

  47. Questioned Documents • Examiners Any document, hand- or typewritten, will be submitted so that authenticity and source can be determined. Ex. ransom notes, suicide notes, death threats, and forgeries • Analysis • Paper Type- Ink Composition • Indentations - Obliterations • Watermark Comparison • Charred or Burned Documents • Matching • Typewritten documents - match machine to its productions. • Inkjets and Laser Printers - matching is nearly impossible. • Handwritten documents – it is original, but no one reproduces writings in the same way twice; rarely provides 100% match FBI Questioned DocumentsUNIT

  48. Other Common Types of Physical Evidence • Plastic Bags – • A polyethylene disposable bag such as a garbage bag may be evidential in a homicide or drug case. • Examinations are conducted to associate a bag with a similar bag in the possession of a suspect. • Plastic, Rubber, and Other Polymers • Remnants of these man-made materials recovered at crime scenes may be linked to objects recovered in the possession of a suspect perpetrator. • Serial numbers • All stolen property submitted to the laboratory for the restoration of erased identification numbers