Criminal Investigations Suspect identification
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Dactyloscopy: the study of fingerprints for ID purposes
Stages of the fingerprint process
Developing Latent prints:1) photograph the item2) photograph the fingerprint itself
different types of fingerprint patterns. (the frequency that they occur in the population)
1) loop - ridges enter one side, re-curve and exit. most common, 60%
2) whorl - ridges encircle a central circular pattern. 35%
3) arch - ridges enter one side, rise in center and flow out the other side (5%)
admissibility of fingerprints (common origins requirements)
Latent fingerprints are compared by experts with the suspects.
since most recovered prints are partial prints, experts compare patterns, and then a point by point comparison.
no specific number of points must be made, but most courts require 10-15 ridges that are identical in both appearance and location to justify a common orgin
Various methods of latent fingerprint development (chemical and non-chemical)
- Latent (invisible) Fingerprint: ridge impressions from sweat pores leave oily residues on surfaces.
- Invisible until something make them visible
- For non-porous materials
- Dusting (most common)
- alternative light sources
- superglue fuming
- small particle reagent
- Porous material
- chemical methods - iodine fuming, ninhydrin
- may produce prints only temporarily, and require immediate photoprahpy
Sound spectrograph is used to convert the sound of the voice recorded on magnetic tape to the visual form.
- Voiceprints: also known as spectrograph, is the only legally admissible voice identification system. it compares acoustical patterns for visual similarities
- no two people have identical vocal chords, nasal cavities, and other body parts responsible for speech
Live-Scan fingerprinting: computerized fingerprint processing and identification. process allows police to place a suspect's fingers on a glass plate for recording (no ink)
Automated fingerprint identification system (AFIS)
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