Summary
Highlights
The session begins with an introduction to forensic science, defined as the application of various sciences, particularly physical science, to aid in legal investigations. The etymology of 'forensic' is traced back to 'forum,' signifying public discussion or legal matters. Criminalistics is introduced as an alternative term, emphasizing the use of science to achieve justice and understand incidents. The discussion highlights the importance of identification in criminal investigation, referencing the 'Law of Multiplicity of Evidence' and illustrating it with the Alice Guo fingerprint case, emphasizing that more similarities in evidence strengthen conclusions.
The lecture transitions to fingerprints, defining them as impressions of fingertips made visible by various substances. Three core principles of fingerprints are explained: Individuality (unique patterns for each individual, with a 1 in 64 billion chance of similarity as per Francis Dalton), Infallibility (reliable and cannot be forged or cheated), and Constancy (permanent from birth to death). Various terminologies related to fingerprint study are introduced, such as dactyoscopy (study of fingers), dactylography (study for personal identification), dactylomancy (personality interpretation), and dermatoglyphics (study of skin patterns).
The anatomy of the finger is discussed, including terms like phalanges (basal, middle, terminal). Common finger conditions like polydactyly (extra fingers), macrodactyly (large fingers), brachydactyly (small fingers), and ectrodactyly (missing fingers) are explained. The speaker also clarifies the structure of friction skin, differentiating between ridges (elevated parts) and furrows (depressed canals), and explaining sweat pores, ducts, and glands.
The discussion moves to fingerprint patterns, specifically the Galton-Henry System with FBI modification and extension. This system includes two arches (plain and tented), two loops (radial and ulnar), and four whirls (plain, central pocket loop, double loop, and accidental). Each pattern is described with its defining characteristics. Arches are the rarest (5%), loops are the most common (60%), and whirls are average (35%). The identification of radial and ulnar loops emphasizes the importance of knowing which hand the print originated from.
This segment details common ridge characteristics, including dots or islands (short ridge formation), bifurcation (one ridge splitting into two), convergence (two ridges combining into one), diverging ridges (two parallel ridges separating), enclosure/eylet (a ridge splitting and then reuniting), ending ridge, typeline (outermost boundary of a pattern), pattern area (where the essential pattern is found), recurving/looping ridge, sufficient recurve (a complete loop with two shoulders), appendage (a short ridge at the summit of a recurve), rod/bar (a short ridge inside a recurve), obstruction (a ridge blocking a recurve), and bridge/crossover (a ridge connecting two parallel ridges).
The critical components of a fingerprint, the core and delta, are explained. The delta is the outer terminus (triangular point), and the core is the inner terminus (center or heart of the pattern). Their importance lies in ridge counting, tracing, and pattern identification. The distinction between 'plain impression' and 'rolled impression' for capturing fingerprints is made, with rolled impressions being crucial for obtaining both core and delta. Rules for selecting the delta (prioritizing bifurcation opening towards the core) and core (innermost recurve, prioritizing rods/bars or shoulders) are meticulously detailed.
Ridge counting, primarily used for loop patterns, involves drawing an imaginary line between the core and delta and counting the ridges that intersect this line, excluding the core and delta themselves. Ridge tracing, applied to world patterns, involves following a 'tracing ridge' from the left delta and determining the number of intervening ridges between the traced line and the right delta. These techniques are foundational for subsequent classification steps.
The discussion introduces the Fingerprint Classification Formula (FPC), which includes preliminary steps like checking (verifying impressions), blocking (identifying patterns using symbols), and classification. The standard size of a fingerprint card (8x8 inches) and the arrangement of finger impressions (right hand 1-5, left hand 6-10, with additional plain impressions for verification) are outlined. The primary division calculation is introduced, where only world patterns are assigned numerical values (16, 8, 4, 2, 1 points based on finger number), and all other patterns count as zero. The sum of points from even-numbered fingers (numerator) and odd-numbered fingers (denominator) is added to a constant +1/+1 to complete the division. Examples are provided to illustrate the calculation.