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Trace Evidence

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  1. Trace Evidence Pleasant Valley High School Forensic Science

  2. The Crime Scene • Processing the Crime Scene • Physical Evidence- any and all objects that can establish that a crime has been committed or can provide a link between a crime and its victim or a crime and its perpetrator • Forensics begins at the crime scene • If the investigator can not recognize, collect, and preserve physical evidence, then there is not any sophisticated technology, lab examination, or technical expertise can salvage the crime scene

  3. The Crime Scene • Not all crimes require the collection of physical evidence • In all reality, most law enforcement agencies do not send out units to any crime other than those deemed major or of a very serious nature • Once the commitment is made to process a crime scene, a moral obligation requires the completion of that process

  4. The Crime Scene • Secure and Isolate the CS • The first officer to respond is responsible for securing and isolating the crime scene • Sometimes the exclusion of unauthorized personnel is difficult • Crimes of a violent nature require more than one officer on most occasions • First Steps: Lead Investigator • Determine boundaries • Establish perpetrator’s entry and exit • Document and photograph obvious evidence • Walkthrough • Develop strategy for completing the investigation

  5. The Crime Scene • Record the Crime Scene • Photographs, sketches, notes

  6. The Crime Scene • Photography • Crime scene must be unaltered • Unless injured parties involved, nothing can be moved • If evidence has been moved, it should be noted in the CS report, but not placed into the CS for photographs • Every photograph must be taken from several angles • If a dead body is in the CS, it must be photographed as well as its position in the room or location • Once body is removed, underneath the body should be photographed • Photograph all pieces of physical evidence from several angles • When size of an item is significant, a ruler should be inserted into the picture

  7. The Crime Scene • Sketches • Rough Sketch- an accurate depiction of scene dimensions and location of all items of interest • Final Sketch- drawn with care and is aesthetic • Prepared with the aid of templates • Must Include: • Location • Time • Date • Incident • Sketched By • Measurement Scale • Key • All Entry and Exit opportunities • North Arrow

  8. The Crime Scene

  9. The Crime Scene • Notes • Constant activity throughout the investigation • Mention every piece of physical evidence collected and rationale for collection • This may be the only source of memory recall after the crime scene • Tape-recording the notes is a good idea • Narrating a video as the scene is investigated is an even better idea • Video or audio must still be transcribed into a written document

  10. The Crime Scene • What to Collect: • Anything from a massive object to a microscopic trace • Some objects are obvious • Other objects take careful testing in the Crime Lab to locate • Example: tiny blood stains on a dark shirt may only be seen through microscopic analysis and chemical testing

  11. The Crime Scene • Deceased Victims: • Pathologist will collect: • Clothing • Fingernail scrapings • Head and pubic hairs • Blood (for DNA typing) • Vaginal, Anal, and Oral Swabs (Sex Crimes) • Recovered bullets from body • Hand swabs from shooting victims (GSR) • After burial, collection of evidence from the body is difficult if not impossible

  12. The Crime Scene • Mobile Crime Laboratory • A major misconception • This is simply a vehicle carrying the required components to secure the scene, preserve evidence, and collect latent prints

  13. The Crime Scene • Collect and Preserve Evidence • Each item must be placed in a separate bag/container • Druggist Fold: Fold into thirds, then into thirds again, tuck and label • DO NOT store bloodstained material in airtight containers • Moisture can cause bacterial or fungal growth and ruin the evidence • Clothing should be air dried and then placed in a paper container • ALWAYS seal burnt/charred debris in an airtight container • Avoid re-entry of moisture into sample

  14. The Crime Scene • Standard/Reference Sample- physical evidence whose origin is known, such as blood or hair that can be compared to crime scene evidence • Reference is important…think back to fingerprints without a reference…they have no value at all

  15. The Crime Scene • Legal Consideration: • Amendment 4 must be followed: • The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizure, shall not be violated, and no warrants shall issue, but upon probable cause, supported by oath or affirmation, and particularly describing the place to be searched, and the persons or things seized.

  16. The Crime Scene • Michigan v. Tyler • Supreme Court upheld that: • We hold that an entry to fight a fire requires no warrant, and that once in the building, officials may remain there for a reasonable time to investigate the cause of the blaze. Thereafter, additional entries to investigate the cause of the fire must be made pursuant to the warrant procedures.


  18. Common Types of Physical Evidence Blood Semen Saliva Documents Drugs Explosives Fibers Fingerprints Ammunition Glass Hair Impressions Physiological fluids Paint Petroleum products Plastic bags Powder residues Serial numbers Soil and minerals Tool marks Vehicle lights Wood and other vegetative matter Physical Evidence

  19. Physical Evidence • Identification • The determining of a substance’s physical or chemical identity • Anniston Crime Lab- primarily used as a drug identification lab • Testing procedures differs with each substance to be tested • For example, you would not test for a white powder to be a base by adding another base to it, you would need to add and acid to see a reaction proving the pH of the unknown • Conclusive results will have to be beyond any reasonable doubt for it to hold up in court

  20. Physical Evidence • Comparison • Put a suspect specimen and a reference specimen through the same test to try to plot a common origin • Example: matching a hair found at a crime scene to that of a suspect who claims to have not been at that location • 2 steps • Combination of select properties to that of the reference specimen and observing • Locate the source of the suspect specimen

  21. Physical Evidence • Individual Evidence- • Properties lead to a source with a high degree of certainty • Examples: • Striations on a bullet, irregular patterns on the bottom of a shoe, fitting together of a piece of shattered glass, matching the box of plastic storage bags to an individual bag through the striations on the bag • It is almost impossible to make a mathematical prediction of how certain the link is, but it is assumed to be more than can be imagined mathematically • French Scientist, Victor Balthazard determined the probability of two people having the same fingerprint to be 1 x 1060 or 1 followed by 60 zeros

  22. Physical Evidence • Class Evidence- • Common to a group of objects or person • Simply knowing the color of a car does not have near the probability of being as accurate as comparing two paint chips and finding an identical match • Product Rule- multiplying together the frequencies of independently occurring genetic markers to obtain an overall frequency of occurrence in a genetic profile

  23. Which is Class and which is Individual?

  24. Physical Evidence • Case: O.J. Simpson Murder Trial • A bloodstain located at the scene of Nicole Brown’s murder was found to include a number of blood factors that matched some blood factors of O.J. Simpson’s blood • The blood factors did not match Nicole Brown or Ron Goldman, the two victims • This eliminated the two victims as the source of that particular bloodstain • One would assume that it would place O.J. Simpson at the scene of the crime…but O.J. is innocent • …and Pigs Fly…

  25. Physical Evidence • The value of class evidence is only a factor when it can be combined with other evidence that is free of human bias • What are some problems with Class Evidence?

  26. Physical Evidence • Crime Scene Reconstruction • The method used to support a likely sequence of events by the observation and evaluation of physical evidence, as well as statements made by those involved with the incident • Protecting the scene plays a role in this step of investigation as well • Using physical evidence and evaluation of witnesses, the investigator must arrange what occurred, when it occurred, and how it occurred • By careful documentation, one can unravel all of the secrets and hidden portions of a crime scene

  27. Physical Evidence • Often times, reconstruction requires the presence of a medical examiner in order to determine natural placement of a body…if the body is in an unnatural position • Medical examiner can determine if body has been moved due to detection of livor (not liver) distribution (enzymes that result in rigor mortis) • It can also be determined if the body was clothed prior to death due to placement of livor distribution. If clothes were on the body, livor will not build up around clothing restricted areas

  28. A criminalist may also be used • A criminalist may be used to implement a laser system to track the path of a bullet in order to determine the position of a shooter • May be used for blood spatter analysis • Determine direction of projections and shapes of broken glass • GSR on clothing

  29. Physical Evidence

  30. Physical Evidence Case Study • The Wayne Williams Trial and the Atlanta Child Murders

  31. The Wayne Williams Trial • In April and May of 1981, Nathaniel Carter and Jimmy Payne were murdered • During an 8 week trial, The physical evidence linking Williams to the two murders and 10 others were presented • The Georgia State Crime Laboratory collected a number of yellowish green fibers and some violet acetate fibers from the bodies and clothing of the victims found from 1979 to1981 • The fibers were very similar and were suspected to be linked to a single source

  32. Williams Trial • The fibers provided hope that the murderer could be found • The yellowish green fibers were lobed and thought to have originated from a rug or carpet • A forensic chemist linked the fiber to a carpet, but was unable to immediately identify the manufacturer of the rare fiber • The Atlanta newspaper printed the identification of the fiber type when two murdered children were found in a river • The two children were clothed only in undergarments in an attempt to prevent further fiber identification

  33. Williams Trial • When the bodies were dumped, police nearby were alerted by a splashing noise and apprehended a man driving away from the scene, Wayne Williams • Two days later, Nathaniel Carter’s nude body was lifted from the water of the Chattahoochee River • A yellowish green fiber was lifted from his hair • The fiber was the linked to the home of Williams • The carpet was then determined to be produced by the Wellman Corporation • It was confirmed through the Wellman Corporation that the fibers did in fact belong in a carpet made by them

  34. Williams Trial • It was also determined that fibers with the specific cross sectional pattern of the collected fibers were produced only between the years of 1967 and 1974 • It was then determined that West Point Pepperell Corporation of Dalton, GA produced a carpet line called “Luxaire” and one of the colors was “English Olive” • Probability Reading on Pg. 79-80 in Criminalistics Book

  35. Williams Trial • Over 40 charts and 350 Photos educated the jury on the probability that the fibers were belonging to Williams • A jury handed down a unanimous guilty verdict on all charges after all evidence was presented against Williams

  36. Glass and Soil • The process of identification only ends when a piece of evidence has been individualized to ONE correct source • Physical Properties: weight, color, boiling point, melting point, smell, taste • Chemical Properties: reactivity, formation of a new substance • For example: in the crime lab, heroin produces a color change when combines with Marquis reagent, positively identifying heroin • Which properties to be observed depends on the substance. Logic requires that if a piece of evidence can be assigned a numerical value, then it must be assigned using the metric system.

  37. Glass and Soil • The Metric System: • Stair Step • Kathy Has Dirty Underwear don’t check mine mister • System based on the base unit of 10 • Some Useful Conversions: • 1 inch = 2.54 cm • 1 m = 39.37 inches • 1 pound = 453.6 g • 1 L = 1.06 quarts • 1 Kg = 2.2 pounds

  38. Glass and Soil • Temperature: • Melting and boiling points are lead indicators of the identity of unknown substances • Fahrenheit – standard units • Celsius – metric units • Key Words: Melting Point, Freezing Point, Boiling Point, Absolute Zero • Weight and Mass: • Weight- the force of gravity acting on a mass • Mass- the amount of matter that an object contains • Mass is independent on the location and or force of gravity • For Example: if you went into outer space, you would not have weight, but you would have mass

  39. Glass and Soil • Density: • Look at the formula above the door • Intensive property- the same regardless of the size of the substance • Refractive Index: • Light can travel in a wave pattern at a speed of 300 million meters per second • The bending of a light wave due to a change in velocity is called refraction • The ratio of the velocity of light to that of any medium is refractive index • Refractive Index = velocity of light in vacuum / velocity of light in medium

  40. Common Densities

  41. Refractive Index

  42. Glass and Soil • Refractive Index: • Crystalline Solids – will have two refractive indices depending on the direction in which light enters the substance • Can produce a double image • Cubic solids produce a phenomenon known as double refraction • Amorphous Solids – no distinctive pattern or number of refractive indices • Using a glass prism, the colors of light can be spread out into the ultraviolet spectrum • This is known as dispersion

  43. Glass and Soil • Glass that is shattered can be used to link a suspect to a crime scene • For example, if a suspect has shattered glass lodged into his/her shoes, and the glass fits into the reconstructed piece of glass from the CS, then the suspect was at one time at the CS • Or…headlight glass found at the scene of an automobile accident can be used to link a driver to the hit and run accident • Glass is a hard, brittle, amorphous solid made by combining silicon oxides and metal oxides and heated to melting and not allowed to crystallize

  44. Glass and Soil • Common Glass Types: • Window and Bottle Glass: • Sand is added to Sodium Carbonate and melted, then Calcium Oxide is added to eliminate solubility and allowed to cool until is forms into glass • Pyrex: automobile headlight and heat resistant glass • Add Boron oxide to bottle glass prior to melting and it will result in borosilicate glass…or in other words: baking dishes or laboratory glassware

  45. Glass and Soil • Tempered Glass • This glass is made by continuous heating, cooling, and heating until the glass is stronger • Tempered glass will not shatter when broken, but will fragment or “dice” into small squares without splintering • Tempered glass is used in automobiles (side and rear windows) • Laminated Glass • This glass is used in the windshields of all cars in the United States • Created by sandwiching a piece of plastic film between two panels of glass

  46. Problems with Glass • Most glass fragments that are presented to a criminalist are too small or fragmentary that they can not be identified

  47. Becke Line • The apparent halo around a particle in liquid of a different refractive index • How is this important? • Certain types of glass give off specific Becke Lines • The halo disappears when the particle and the fluid have similar refractive indices

  48. Glass Fractures • The penetration of ordinary window glass by a projectile, it produces a fracture pattern that cracks and radiates outward and encircle the hole • The radiating lines are called radial fractures • The concentric circles are called concentric fractures • When a high speed projectile penetrates glass, an almost identical pattern flows around the entry point with a wider hole at the exit side • This is key to determining the direction of a shot

  49. Existing Fractures • If two shots were fired, then the second fracture will stop when it comes in contact with the previous fracture

  50. Soil • For forensic purposes, soil is any disintegrated surface material that is on or near the earth’s surface • Low power microscopic examination of soil will reveal the presence of plant and animals materials as well as artificial debris • Soil identification requires the aid of a person specialized in forensic geology or general geology