ABSTRACT
A. The Relationship of Evidence to Source ............................................. 114 1. Principle, Process, or Objective .................................................... 115 2. The Question of Source................................................................ 116
B. Classification — Categorization with Like Items............................... 116 1. Class Characteristics...................................................................... 117
a. Class Characteristics Result from a Controlled Generation Process................................................................. 118
b. Items with the Same Class Characteristics May Have Different Origins .................................................................... 119
c. When Is Evidence Class Evidence? ....................................... 121 C. Identification ......................................................................................... 122 D. Individualization................................................................................... 122
1. A Conclusion of Common Source............................................... 123 2. Individuality and Uniqueness....................................................... 123
a. Existent Objects Are Unique ................................................. 123 b. The Generation of Individual Characteristics ..................... 124
i. Generation by Nature ................................................... 124 ii. Generation by Man....................................................... 125
iii. Entropy and Disorder................................................... 125 c. The Scale of Detection Is Determined by the Scale of
Manufacture ........................................................................... 127 i. Signal vs. Noise ............................................................. 128
3. Individualizing Characteristics ..................................................... 129 4. Physical Evidence with Individualizing Potential ....................... 129 5. The Conceptual Process of Individualization ............................. 130
a. Analysis of Evidence for Class and Individualizing Characteristics ........................................................................ 131
i. Collection and Preservation......................................... 131 ii. Examination .................................................................. 131
E. Inferring a Common or Different Source........................................... 137 1. Conclusion, Inference, or Opinion of Common Source............ 137 2. Three Inferences ............................................................................ 138
a. The Items Originate from Different Sources ....................... 138 b. The Items May Be Classified, but Cannot Be
Individualized Due to a Limitation of the Evidence or the Test .................................................................................... 139
c. The Items Share a Unique Common Origin ....................... 139 d. The Conclusion ...................................................................... 140
F. Mathematical Approaches to Expressing the Strength of the Inference ................................................................................................ 140 1. The Necessity of Providing an Assessment of the Strength
of the Inference.............................................................................. 140 2. Tools for Estimating the Strength of the Inference .................... 141
a. Frequency Estimates............................................................... 142 b. Likelihood Ratios ................................................................... 142
i. Likelihood Ratios in Bayes’ Theorem.......................... 144 3. Classification.................................................................................. 145
a. Hypothesis Testing vs. Bayes’ Theorem — Which One?..... 147 4. Individualization ........................................................................... 147
a. Individualization and Opinion — A Special Case .............. 148 G. Summary ............................................................................................... 150 References ...................................................................................................... 151
In
Crime Investigation
(1953), Kirk suggests that the central task of the criminal investigator is to establish personal identity. He continues to say that supplementary to this task is the identification of physical objects that may, in turn, contribute to the desired personal identification. Kirk outlines the issues and difficulties inherent in the endeavor to establish personal identity through clues provided by physical evidence. In this chapter, we continue that discussion.
