(two loops that create an S-like pattern), and accidental loop (irregular shaped). Whorls account for approximately 35 percent of all pattern types ( see Figure 3 6 ) . Analysts use the general pattern type (loop, whorl or arch) to make initial comparisons and include or exclude a known fingerprint from further analysis. To compare a fingerprint, the analyst uses minutiae , or ridge characteristics , to identify specific points on a suspect fingerprint with the same information in a known fingerprint ( see Figure 4) . For example, an analyst comparing a crime scene fingerprint to a fingerprint on file would first gather known fingerprints with the same general pattern type, then compare the fingerprints side-by-side to identify specific minutiae that are consistent between the known and unknown print. If enough details correlate, the fingerprints are determined to be from the same person. Figure 4: Minutiae Patterns. There are three types of fingerprints found by investigators at a crime scene. Patent fingerprints, or visible fingerprints, are left on a smooth surface when blood, ink, or some other liquid comes in contact with the hands and is then transferred to that surface. Plastic fingerprints are indentations left in some soft material such as clay, putty, or wax. Latent Figure 3: Whorl Patterns.
SCI 114 – Scientific Principles of Forensic Science Laboratory Exercise: Fingerprint Analysis Page 3 of 7 fingerprints , or invisible fingerprints, are formed when the body’s natural oils and sweat on the skin are deposited onto another surface. Latent fingerprints can be found on a variety of surfaces; however, they are not readily visible. Their detection often requires the use of various methods to develop the fingerprint in order to become visible. For example, they can be visualized by dusting with powders or applying specific reagents. Latent Fingerprint Development Techniques Dusting: One of the most common methods for visualizing and collecting latent fingerprints is by dusting a smooth or nonporous surface with fingerprint powder. Powder brushed lightly over a latent-bearing surface will cling to grease or moisture in the ridges of a latent fingerprint, making it visible against the background. A powder that will contrast with the color of the surface must be used. If any fingerprints appear, they are to be photographed and then lifted with clear adhesive tape. The lifting tape is then placed on a latent lift card to preserve the fingerprint. i Cyanoacrylate: Another common latent fingerprint development technique is cyanoacrylate (superglue) fuming of a surface, which is used prior to applying powders or dye stains. This process is typically performed on non-porous surfaces and involves exposing the object to cyanoacrylate vapors. The vapors will adhere to fingerprint impressions present on the object, creating a white impression. Several post-cyanoacrylate dye stains or powders may be applied to improve the visualization of the developed detail .
You've reached the end of your free preview.
Want to read all 7 pages?
- Spring '14