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Firearm & Toolmark Identification. Introduction. The following resource is provided by the Scientific Working Group for Firearms & Toolmarks (SWGGUN) to assist forensic experts in describing the scientific basis of their discipline in preparation for evidence admissibility hearings.

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Firearm & Toolmark Identification


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    1. Firearm & Toolmark Identification

    2. Introduction The following resource is provided by the Scientific Working Group for Firearms & Toolmarks (SWGGUN) to assist forensic experts in describing the scientific basis of their discipline in preparation for evidence admissibility hearings. The material posted here is for you to prepare yourself when educating the criminal justice system. The information contained within this presentation was not designed to be all-inclusive and can be adapted to meet your specific needs.

    3. Outline • Basic Overview of Science & Forensic Science • Fundamentals of Firearm & Toolmark Identification • The Five Prongs of Daubert • Summary

    4. Basic Overview of Science & Forensic Science • What is Science? • Scientific Method • To be Scientific… • What is Forensic Science?

    5. Basic Overview What is Science? • A systematic gathering of knowledge. • The observation, identification, description, experimental investigation and the theoretical explanation of phenomena.

    6. Basic Overview Scientific Method Procedures for the systematic gathering of knowledge. These procedures generally involve: • Stating a problem • Developing a hypothesis • Testing a hypothesis • Forming a theory • Using theories to predict events

    7. Basic Overview To be Scientific… • The theory must be testable. • The theory must be validated through the testing of the fundamental propositions upon which the science is based.

    8. Basic Overview What is Forensic Science? The application of scienceto law.

    9. Fundamentals of Firearm & Toolmark Identification • Definitions • Fundamental Propositions (1 & 2) • Examination Method • Range of Conclusions

    10. Definition: Firearm & Toolmark Identification Fundamentals of Firearm & Toolmark Identification An empirical comparative analysis that can determine if a striated or impressed mark was produced by a particular tool.

    11. Definition: Tool The harder of two objects that comes into forceful contact with one another, resulting in the softer object being marked. Fundamentals of Firearm & Toolmark Identification

    12. Definition: Toolmark Fundamentals of Firearm & Toolmark Identification Features imparted on an object by the contact and force exerted from a tool. • Two Types – • Impressed Toolmarks • Striated Toolmarks

    13. Definition: Impressed Toolmark Fundamentals of Firearm & Toolmark Identification Features produced when a tool contacts an object with enough compressive force that it leaves an impression.

    14. Definition: Striated Toolmark Fundamentals of Firearm & Toolmark Identification Features produced when a tool contacts an object with lateral force and motion.

    15. Fundamentals of Firearm & Toolmark Identification The Science of Firearm & Toolmark Identification is based on two fundamental propositions:

    16. Proposition #1 Fundamentals of Firearm & Toolmark Identification Toolmarks imparted to objects by different tools will rarely if ever display agreement sufficient to lead a qualified examiner to conclude the objects were marked by the same tool. That is, a qualified examiner will rarely if ever commit a false positive error (misidentification).

    17. Proposition #2 Fundamentals of Firearm & Toolmark Identification Most manufacturing processes involve the transfer of rapidly changing or random marks onto work pieces such as barrel bores, breechfaces, firing pins, screwdriver blades, and the working surfaces of other common tools. This is caused principally by the phenomena of tool wear and chip formation, or by electrical/chemical erosion. Microscopic marks on tools may then continue to change from further wear, corrosion, or abuse.

    18. Definition: Class Characteristics Fundamentals of Firearm & Toolmark Identification General and/or measurable features of a specimen which indicate a restricted group source. They result from design factors, and are therefore determined prior to manufacture.

    19. Fundamentals of Firearm & Toolmark Identification Examples of Class Characteristics Questioned Item: Bullet Known Source: Rifling

    20. Examples of Class Characteristics Fundamentals of Firearm & Toolmark Identification Corresponding Blade Dimensions

    21. Definition: Subclass Characteristics Fundamentals of Firearm & Toolmark Identification Features that may be produced during manufacture that are consistent among some items fabricated by the same tool. These are not determined prior to manufacture and are more restrictive than class characteristics.

    22. Example of Subclass Fundamentals of Firearm & Toolmark Identification

    23. Definition: Individual Characteristics Fundamentals of Firearm & Toolmark Identification Marks or features produced by the random imperfections or irregularities of tool surfaces. These characteristics can be used to individually associate a tool to a toolmark.

    24. How are individual characteristics produced? Fundamentals of Firearm & Toolmark Identification These random imperfections or irregularities can be produced by: • Manufacture • Wear from Use • Wear from Abuse

    25. Example of Individual Characteristics from Manufacture Fundamentals of Firearm & Toolmark Identification

    26. Example of Individual Characteristics from Wear Fundamentals of Firearm & Toolmark Identification UseAbuse

    27. Examination Process Fundamentals of Firearm & Toolmark Identification Level 1 analysis - Class Characteristics • Elimination, but not individualization, can occur here

    28. Examination Process Fundamentals of Firearm & Toolmark Identification Level 2 analysis - Comparison Microscopy • Individualization occurs only here

    29. Range of Conclusions Fundamentals of Firearm & Toolmark Identification • Identification • Inconclusive • Elimination

    30. Range of Conclusions - Identification Fundamentals of Firearm & Toolmark Identification If the quality and character of the toolmark have sufficient detail, an identification can be concluded based on the correspondence of individual characteristics.

    31. Examples of an Identification Fundamentals of Firearm & Toolmark Identification

    32. Range of Conclusions - Inconclusive Fundamentals of Firearm & Toolmark Identification If the quality and character of the toolmark are lacking, an examiner may not be able to make an identification or elimination. In this case an inconclusive result would be the appropriate response.

    33. Examples of an Inconclusive Fundamentals of Firearm & Toolmark Identification

    34. Examples of an Inconclusive Fundamentals of Firearm & Toolmark Identification

    35. Range of Conclusions - Elimination Fundamentals of Firearm & Toolmark Identification • If significant disagreement in class characteristics exists, an elimination conclusion would be the appropriate response. • If disagreement in individual characteristics of an exceptional nature exists, an elimination conclusion may be the appropriate response.

    36. Examples of an Elimination Fundamentals of Firearm & Toolmark Identification

    37. Examples of an Elimination Fundamentals of Firearm & Toolmark Identification

    38. Basis for Firearm & Toolmark Identification • Standards of Identification • Objective vs. Subjective Examinations • What makes an Identification possible? • Significance of Conclusions

    39. Identification Standard - I • Basis for Firearm & Toolmark Identification “The Theory of Identification as it pertains to the comparison of toolmarks enables opinions of common origin to be made when unique surface contours of two toolmarks are in ‘sufficient agreement.’” Objectively stated AFTE Identification Standard (1992)

    40. Identification Standard - II • Basis for Firearm & Toolmark Identification “Agreement is significant when it exceeds the best agreement demonstrated between toolmarks known to have been produced by different tools and is consistent with the agreement demonstrated by toolmarks known to have been produced by the same tool.” Objectively stated AFTE Identification Standard (1992)

    41. Identification Standard Summary • Basis for Firearm & Toolmark Identification In the application of the objective AFTE Theory of Identification Standard, a subjective determination must be made by a qualified examiner as to the amount of agreement necessary for an identification to exist.

    42. Basis for Firearm & Toolmark Identification Definition: Objective Examination An objective examination is one that can be repeated by different scientists and if using the same type of equipment and following the same procedures, will result in essentially the same conclusions every time.

    43. The results of a subjective examination are based on an individual’s opinion. This does not mean that this type of examination is unreliable or unscientific. There is subjectivity in every science and in every test, whether it being a doctor diagnosing a head cold or a chemist determining where to set the base line on a scientific instrument. • Basis for Firearm & Toolmark Identification Definition: Subjective Examination

    44. What makes an identification possible? • Basis for Firearm & Toolmark Identification • Proposition #2 • A sound examination method • By employing the precepts of empirical research or study in the comparison of two toolmarks. • Specialized training to develop cognitive skills • An examiner undergoes standardized technical training that develops cognitive skills to recognize, differentiate and understand the patterns of marks and their uniqueness.

    45. Significance of Conclusions • Basis for Firearm & Toolmark Identification • Based on Propositions #1 and #2, an individual association or identification conclusion can be effected. These individual associations result from the “practical certainty” of the validated theory and not from “absolute certainty”.

    46. Five Prongs of Daubert • Testability • General Acceptance • Peer Review • Known or Potential Error Rate • Maintenance of Standards & Controls

    47. Five Prongs of Daubert- Testability Definition: Testability A critical evaluation process that supports or refutes a hypothesis.

    48. Five Prongs of Daubert- Testability What evidence exists to support the science of Firearm & Toolmark Identification? Numerous empirical and validation studies of consecutively manufactured tools have been published over the past 50 years.

    49. Five Prongs of Daubert- Testability Consecutive Manufacture Studies: Gun Barrels (Cut Rifling) • Lutz (1970) • Skolrood (1975) • Brown & Bryant (1995) • Brundage (1998) • Miller (2000)

    50. Consecutive Manufacture Studies: Gun Barrels (Forged Rifling) Murdock (1981) Hall (1983) Matty (1985) Electrochemical Rifling DeFrance (2003) Five Prongs of Daubert- Testability