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Lecture 20 Microscenes: Trace Evidence - Hair and Fibers

Lecture 20 Microscenes: Trace Evidence - Hair and Fibers

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Lecture 20 Microscenes: Trace Evidence - Hair and Fibers

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  1. Lecture 20Microscenes: Trace Evidence - Hair and Fibers • The most common forms of trace evidence are bloodstains, hair, textile fibers, paint, and glass fragments. • Crime scene investigators • Aware that microscopic particles at scene comprise part of that environment • What is linked to the crime. • Collecting both is critical to the success of an investigation

  2. Theoretical Framework of Forensic Analysis • Over the last several decades, a theoretical framework of sorts has evolved. • Fundamental concepts provide a philosophical and rational framework for the application of scientific knowledge to the forensic arena. • Concepts that guide forensic analysis in a logical progression, • Start with understanding of the origin of evidence, • Culminates in a statement of the significance of an analytical result. • Unfortunately, these concepts have evolved in a fragmented manner and, in fact, • No published record of a comprehensive organized paradigm exists. • Forensic scientists understand that the major paradigm comprises five basic concepts • Transfer ….(Locard exchange principle) • Identification ….(placing objects in a class) • Individualization ….(narrowing the class to one) • Association …. (linking a person with a crime scene) • Reconstruction (understanding the sequence of past events) Forensic Science International 126 (2002) 11–16

  3. The Theoretical Framework Not basic scientific principles • Recognition • Analysis • Interpretation of physical evidence. • Identification • Individualization • Association • Reconstruction Relate Better

  4. Divisible matter—a fundamental principle in forensic science

  5. Classifying Evidence at Crime Scenes Relationship of Macro and Microscenes

  6. Locard Exchange Principle

  7. Microscene Elements • The Principle of Divisible Matter and The Locard Exchange Principle reflects. The relationship between the macroscene and microscene elements. • Hair and fiber evidence are examples of microscene elements at crime scenes. • Fibers represent a vast array of trace evidence • Differ chemically and structurally (except for wool and cotton which are natural fibers) from hair, • Not discussed individually because collecting hairs and fibers at the scene involve fundamentally the same procedures. • Many consider hairs and fibers as a class of “fibers,” and there is often the term, “hair fiber”. • The term makes little sense, but this lexicon has become ingrained. • Collected at the same time • from the same items of evidence, they are considered similarly and rightfully as classes of trace evidence.

  8. Associative Evidence • Hair and Fiber evidence is associative evidence • Tilts the scale toward or away from guilt rather than pointing a finger directly at an individual. • Normally, microscopic comparison of hairs does not identify a specific person, but like fiber evidence, It has intrinsic investigative value. • Demonstrate that there may have been an association between • A suspect and a crime scene • A suspect and a victim • Demonstrate that no evidence exists for an association between a suspect and a crime scene or a suspect and a victim. • Both statements illustrate the associative value of hair evidence • Microscopic hair comparisons have been discredited through testimony and follow-up exonerations by DNA analysis • Still important to help exculpate or inculpate.

  9. Hair and Fibers as Evidence • Seemingly ubiquitous, • Should be a focus of macroscene and microscene scene investigations. • From a search perspective, hair and fibers are visible or can be made visible using light sources. • Straddle the macroscene and microscene sphere. • Hair at the scene can come from animals or humans • Fibers come from plants or are manufactured synthetically • Can be a source of associative physical evidence. • The problem is that there is too much • Deciding where to find them and then which to collect can be daunting. • People and animals are continuously shedding hair. • The same is true for fibers with certain caveats. • Essentially, we leave a trail of fibers, too, but to a lesser extent.

  10. Hair Evidence • During a violent physical encounter, hair is lost quite easily though shedding and/or pulling, • Most people have hair on their bodies, even bald men: body, armpit (axillary), head hair, pubic hair, and beard hair. • Readily collected, identified, and compared. • The same is nearly true for fibers because the contact that occurs during a struggle creates an energy that fosters the transfer of fibers. • Compared: • Operative word for what happens in the laboratory and for the importance of hair and fiber evidence in the court during testimony. • The laboratory criminalist has the responsibility to compare scene-collected hair and/or fibers with exemplars collected from individuals, suspects, witnesses, victims and/or their clothing. • Historically, hair evidence has enjoyed an elevated stature in the courts and with juries because it has been presented as scientific evidence having an infallible ability to make matches. • Aftermath of the NAS report, • The forensic value of microscopic hair analysis has been tempered. • NAS report recommends using microscopic hair comparisons as a pre-screen for follow-on mitochondrial DNA typing.

  11. Importance of Microscopic Hair Evidence • Identify hair’s structural characteristics microscopically and using them as a basis of comparison, • Hair’s importance: It contains DNA. • Because cellular material forms its root, which becomes trapped in the hair shaft as it grows. • Fiber analysis is much simpler in concept because the analysis of fiber evidence can only identify the type of fiber, e.g., rayon, cotton, wool, etc, and the dyes used in its manufacture. • Other forensic information can identify other characteristics, which can help substantiate or repudiate witness statements or other soft, factual evidence • burned, • cut, • pulled, etc,. • Fiber analysis is much simpler in concept because the analysis of fiber evidence can only identify the type of fiber, • Rayon, cotton, wool, etc, and the dyes used in its manufacture • Fibers do not have the gold standard of evidence, DNA.

  12. DNA in Hair • The basic structure of hair, from a DNA perspective, is simple. • Understanding forensic value requires knowledge of describe its growth cycle. • From a scene investigative perspective, a quick look at the root end of a found hair can tell a lot about its potential forensic value. • This single observation can reveal a lot about what will happen to the hair in the forensic laboratory and how valuable it will be as evidence. • Diagnostic physical features easily observed with magnifying glass • Can help ascertain whether the diagnostic features are present and whether genomic DNA analysis will be successful. • Does not mean DNA analysis will not be successful • mtDNA analysis

  13. The Growth Cycle of Hair • Hair’s growth cycle has three phases: • Anagen, • Catagen • Telogen. • Each phase has important forensic consequences with respect subsequent DNA analysis,.

  14. Anagen or Growth Phase of Hair Hair Shaft Not So Much Genomic DNA • The anagen phase of hair growth is the longest, • Two and six years. • As hair grows, dead cells and keratin (protein) are pushed out through the scalp. • The sebaceous glands produce sebum, an oily substance that helps to condition and protect the hair. • At any one time, approximately 80-95% of the hairs on a human head are in the anagen phase • During a struggle, hair in the anagen growth phase can be yanked from the head. • A strong tug will forcibly remove hair that has a group of cells attached to the root end. • Typically an abundance of these root sheath cells, • Should be visible with & without a magnifying glass. • A follicular papilla might also be attached. • These cells have nuclei, and there will sufficient cellular material to perform genomic DNA testing, the DNA typically analyzed to identify someone. • Sometimes even brushing ones hair can pull out root sheath cells Root Sheath Cells Lots of Genomic DNA • Roots appear dark and fleshy and might have some pigmentation. • Adhering root sheath cells extremely fragile • Easily lost. • Examining through magnifying glass is acceptable. • Extreme care must be taken to preserve them.

  15. The Catagen or Transitional Phase of Hair Growth • Next hair enters catagen or transitional phase. • The sebaceous glands produce less oily sebum and the • Hair stops growing. • Root stops growing and starts forming a blunt, club-like appearance. • This “club hair” forms as part of the hair follicle that attaches to the hair shaft, • Prevents the hair from receiving nourishment from the blood supply. • After one to two weeks, the hair enters the telogen phase. • At any time, approximately 2% of head hairs are in the catagen phase. Hair Follicle Some Genomic DNA

  16. The Telogen or Inactive Phase of Hair Growth • Lasts for approximately three months. • The hair remains attached to the head but is not growing. • In essence, it is resting and inactive. • Hair follicle stops producing keratin and the club end goes to completion. • Club hair is fully formed, • Seen as a white, hard lump when the hair sheds. • Phase is complete when hair is shed. • At any one time, approximately 10-18% of head hairs are in the telogen phase • Approximately 100 head hairs are shed daily. Fully Formed Club End Almost no useable Genomic DNA

  17. DNA and the Structural Parts of the Hair • Hair contains two types of DNA: genomic and mitochondrial (mtDNA). • Genomic DNA • Preferentially analyzed to identify the source of scene-related biological evidence, e.g. blood, semen, saliva, etc … • Found in the cell nucleus • Comprised of equal contributions from the mother and the father. • Mitochondrial DNA is different structurally and genetically. • Inherited from the mother • Analyzing mtDNA can be important. Does not have the identifying power of genomic DNA. • Investigator would prefer to find biological samples having genomic DNA. mtDNA next best thing --- can provide strong inculpatory evidence and it can exculpate absolutely.

  18. Transfer and Persistence of Hair • Few studies have been done concerning either the persistence or the transfer of hairs. Several studies have been done concerning the persistence of fibers. • Transfer of Hair at the Scene • Locard believed that there would always be a transfer of trace evidence, whether hairs, dust, or fibers … not to imply evidence will always be found … could be too … might have been lost. • Most common evidence transfers primary, which occur during the commission of the crime. • Secondary transfers are also possible, but although not the object of the crime scene search, they can take place and can deposit non-crime-related evidence. • From the perpetrator to the scene – Primary transfer • To the perpetrator from the other participants, e.g., the victim(s) – Primary transfer • To the perpetrator from the scene - Primary transfer • From the other participants to the scene – Primary transfer

  19. Transfer of Hair at the Scene • Primary transfer is most important … showing that an arrested person was at the scene. • Probability of transferred hair evidence is fairly high. Knowing evidence should be there … formulate a search strategy to locate … then apply appropriate techniques to collect. • Areas where the probability of the transfer is the highest. • Locard: Area of struggle is where energy expended. • Logically, then, this is where highest likelihood of finding anagen hairs; those having with the highest potential for DNA analysis. • Logic dictates other areas where hair evidence might be, e.g., ski masks are a common type of evidence and the clothing of the victim is another source of hair evidence. • Rule of thumb: For Collecting Hair & Fiber Evidence • If possibility of losing evidence during transfer … • Collect at the scene. For example, if there are hairs on the clothing of the deceased in death investigation … collect the hairs at scene, after performing the appropriate archiving procedures.

  20. Persistence of Hair Greatest Loss in 1st 30 Minutes • The effects of artificial dyeing of hairs, the presence or absence of roots and different types of fabrics on the persistence of hair on a variety of garments were investigated. • The garments were made from cotton, polycotton, cotton/acrylic, polyester and wool. • The results indicated that neither artificial dyes nor the presence or absence of roots had statistically significant effects on the persistence of hair. • In contrast, the type of fabric had a major impact and it was found that, generally, hairs persist longer on rougher fabrics. • The rate of loss of hairs from non-woollen fabrics during normal wear was found to follow an exponential decay curve. • In contrast, the rate of loss from the woollen garments was quite linear, indicating a constant, even loss, and thus suggests that a different process is involved in the persistence of hairs on woollen garments from that on non-woollen garments. • The speed at which hair was lost from fabrics decreased in the order polyester, cotton/acrylic, polycotton, cotton, smooth wool, rough wool • Wool gives the best chance of recovering samples of hair. Animal Hairs on Wool – 82%/30 min Polyester – 25% 30 min Dachs J, McNaught IJ, Robertson J. Forensic Sci Int. 2003 Dec 17;138(1-3):27-36.

  21. Recovery of Hair Evidence Occurs in Two Locations • At the crime scene • In the laboratory. • The laboratory has the better facilities, as much hair recovery as possible should be conducted there. • If an item suspected of having adhering hairs is portable, • Best method of hair recovery at the scene is to seize and carefully package the entire item. • Each exhibit item should be packaged immediately in its own separate container. • Clean bags with no exposed inside seams are the best containers for clothing and other large items. • Clear plastic vials or metal ointment tins are recommended for small objects. • To prevent accidental contamination, exhibit items in an unpackaged state should not be handled by more than one investigator. By placing clear cellulose tape in contact with the area in question, hairs can be recovered from items which cannot practicably be brought to the laboratory.

  22. Collecting and Preserving Hair at the Scene • As crucial as finding the evidence in the first place. • Extreme care must be taken to guarantee that the evidence is not contaminated or lost. • Proper legal procedures must be taken into account so that the evidence is not lost to any legal proceeding. • The Scientific Working Group on Materials Analysis (SWGMAT) promulgated guidelines for the collection and preservation of trace evidence . • The document is divided into several sections that are summarized and paraphrased for on-scene considerations as follows.

  23. Archiving • Create a case file for the specific case. • The file must contain the case documentation for the length of time required by the prevailing laws and non-conflicting agency policy. • Record important case-specific information • Date and time, when appropriate, of the collection, • Name of person(s) collecting the evidence, • Description of items collected, • Assign a unique identifier for each item collected • Record location of each item (documented by notes, sketches, measurements, photographs or a combination).

  24. Trace Evidence Collection and Preservation Techniques • Always employ logic and scientific method • Applies to the finding, collecting and preserving trace evidence. • An aspect of this logical approach is the need to consider the scene from a holistic perspective … considering everything the scene has to offer: the particulars of the incident case and the conditions at the scene and/or the surrounding area. • Develop decision tree for collecting, packaging and preserving the evidence. • What is the best method for collecting the evidence? • Will collecting the evidence compromise the evidence’s integrity and thus the laboratory’s ability to analyze it? • How should it be packaged and preserved until it gets to the laboratory? • Record Keeping • Record the scene location of the evidence and the techniques used for detection, collection, and preservation on an appropriate form.

  25. Contamination and Loss • Use appropriate procedures to prevent contamination and loss. • Confer with other scene investigators to ensure that trace evidence is not lost as a result of testing or collection of other evidence. • General principles and practices to avoid evidence contamination and loss: • Restrict contact between items and personnel before the trace evidence has been secured • Wear appropriate protective apparel, e.g., laboratory coats and disposable gloves, to prevent contamination. • Change as necessary to avoid contamination or transfer between evidentiary items, locations, and personnel. • Handle trace evidence as little as possible to minimize loss and exposure to contaminants. • Collect, package, and seal items individually in appropriate packaging. • Keep items in a secure, sealed package until processed in a controlled environment. • Use clean equipment during collection and examination. • Use uncontaminated adhesive lifting materials. • Ensure that tape edges do not contact unclean surfaces. • Ensure there is adequate lighting for locating, packaging and preserving evidence. • If possible, package evidence in an area that has no excessive air currents, static electricity or excessive foot traffic. • Document in the case file instances where contamination or loss occurred or could have occurred.

  26. Collection Techniques • Use different types of illumination --- oblique lighting with flashlights and alternate light sources (UV, laser, high intensity); and assisted by magnification. • Protecting the evidence is critical, so recovering and collecting trace evidence should be as least intrusive as possible. • The usual collection techniques include picking (with tweezers), lifting (with tape), scraping, vacuum sweeping, combing, and clipping. • For on-scene work, most common is picking, tape lifting and vacuuming. • If a dead body is present, the ME determines whether trace evidence from fingernails will be collected @scene or @ autopsy. • If decision is to collect samples during the autopsy, the hands of the victim (deceased) should be bagged using paper bags. • If samples are collected at the scene, the hands should be bagged to protect what might have been missed. • Techniques performed in sequence, e.g., a cascade. • Picking or Hunt and Peck - Lifting surface evidence easily visualized by the naked eye or by a light source. • Tape lifting: picks up the more embedded evidence. • Vacuum sweeping is the last in the sequence because it picks up the tiny bits of material. It is also the least favorite type of evidence to examine in the laboratory.

  27. Picking (Hunt and Peck). Trace evidence can be separated from an item, e.g., clothing, using clean forceps or other implements. The collected samples should be immediately protected against loss or contamination. • Picking Microscene • Elements at the Scene • First: Naked eye with flashlight or the white setting on the ALS to locate hair or other trace evidence, e.g., fibers, dirt, debris, etc. • Second: ALS’s other wavelengths in the following order, depending of the specific ALS being used: • UV(300-400nm), • CSS (if using the MiniScope), • 415 nm and • 535 nm. • Each wavelength highlights trace evidence with spectral characteristics.

  28. Tape Lifting • Firmly pat or roll an adhesive-bearing tape over an item. • Tape picks up loosely adhering trace evidence. • Do not overload the tape. • Place tape & collected material on transparent backing, e.g., clear plastic sheeting, glass slides, and clear plastic or glass petri dishes. • Clear protective material protects against contamination and permits samples to be easily viewed and removed for further comparison in the laboratory.

  29. Trace Evidence Collection Techniques • Scraping • Clean spatula or similar tool - dislodge trace evidence from an item onto a collection surface, e.g., clean paper, etc. Package the collected debris immediately to avoid sample loss & mix up. Usually a laboratory method because it is in a controlled environment that reduces the risk of contamination or loss of evidence. • Vacuum Sweeping. • A vacuum cleaner equipped with a filter trap is used to recover trace evidence from an item or area. The filter and its contents should be immediately packaged to avoid sample loss. The appropriate vacuum components, the filter and trap must be changed and rigorously cleaned between each vacuuming to avoid contamination. Subsequent to other collection techniques. It is indiscriminate and can result in the collection of a large amount of extraneous material. • Combing. • Combing is used to recover trace evidence from the hair of witnesses, suspects, and victims. Use a clean comb or brush for each combing. Package the combings with the combing device in the same package. • Clipping. • Trace evidence can be recovered from fingernails by nail clipping, scraping, or both. Fingernails from the right and left hands are packaged separately, which does not preclude collecting each or any nail separately from all others, such as a nail with obvious damage. Clip fingernails with clean scissors or clippers and package them in clean paper.

  30. Scrapping Fingernails • Use clean implement to collect debris from under the fingernails. Package the collected debris and the scraping device together in clean paper and seal appropriately • Packaging Fingernail clipping or scrapings • Use packaging that prevents loss and contamination. • Seal packages properly so that edges do not have openings. Do not use saliva to seal adhesive on packaging. • Secure small or loose evidence in clean, unused primary containers such as paper packets, petri dishes or appropriate vials. • Seal the primary container in an envelope or paper bag, which is also sealed and labeled appropriately. • Secure large items, such as whole garments, individually and in clean, unused packaging • Air dry wet clothing before packaging in a location that is free from excessive air currents and foot traffic. • Place paper under the drying clothing to catch trace evidence that might fall off. • Document properly and package intact visible and firmly attached small or manageable items. • Document, collect and package visible but easily lost evidence. • Document and collect evidence from items that impractical to transport. • Always consider the possibility of physical matches when examining trace evidence. These matches should be documented and the item(s) collected and packaged properly.

  31. Evidence Security • Store in secure, controlled-access area. • Must have a documented and continuous chain of custody from the time it was collected at the scene until it is admitted into court or the case has been disposed and the evidence is no longer needed. • Even then, new evidence can warrant a re-investigation of the case, which means that someone might need to reanalyze the evidence. • ASTM Standard Practice E 1492-92 (Standard Practice for Receiving, Documenting, Storing, and Retrieving Evidence in a Forensic Science Laboratory has standards for evidence handling in a forensic laboratory. • These standards represent good forensic and laboratory practice, and they are fundamentally applicable to the crime scene and the laboratory.