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Chapter 19: Friction Ridge System
19.1: Friction Ridges
Friction ridges appear on the palms, soles, and ends of the fingers and toes.
Primary Friction Ridges – develop deep in the dermal layer of the skin.
At about 14 weeks of gestation, sweat glands and sweat ducts begin to form. They infiltrate into the dermis and develop into mature ducts and glands.
The PFR continues to proliferate until the 15th week or 17th week of gestation.
Secondary Friction Ridges – develop from week 17 and mature by week 24.
Friction ridges develop in utero and remain the same throughout life, barring some sort of scarring or trauma to the epidermal dermal margin of a friction ridge area.
What is a Friction Ridge Print made of?
Friction ridge print – a representation of a friction ridge pattern in some medium. It can be classified as either patent, if they are visible with the unaided eye, or latent if they require some sort of assistance to make them visible.
Patent Prints – can appear because of some transferable material on the ridge pattern or because the ridge pattern was transferred to a soft substrate that had “memory” and retained the impression.
Latent Prints – composed of the sweat and oils of the body that is transferred from the ridge pattern to some substrate.
Fingerprint powder: Most familiar visualizing technique; is colored, fluorescent, or magnetic materials that are very finely ground, which is brushed lightly over a suspected print to produce contrast between the background and the now visible print.
19.2: Collecting Prints at Crime Scenes
Visualization Method | Use | Limitations |
|---|---|---|
Amino Black | Protein dye is sensitive to blood, turning a blue-black color in its presence. Treatment with a physical developer may be done after amido black to improve the developed print. | It will not stain the normal constituents in a latent print. Amido black should not be used as a presumptive test for blood because it reacts to more than only blood. |
Aqueous amido black | The protein dye solution is sensitive to blood, turning a blue-black color in its presence. Treatment with a physical developer may be done after amido black to improve the developed print. Can be washed over any nonporous surface; the item may also be submerged in the solution. | It will not stain the normal constituents in a latent print. Amido black should not be used as a presumptive test for blood because it reacts to more than only blood. May permanently stain some surfaces. Presumptive blood tests should be done before using aqueous amido black. It is corrosive and will damage metal surfaces if not washed off quickly. |
Aqueous leucocrystal violet | Enhances and develops latent prints stained with blood on porous or nonporous surfaces. Best applied by washing or submersion. | It will not stain the normal constituents in a latent print. May permanently stain some surfaces. |
Gentian crystal violet | A protein-dye that stains the fatty portions of sebaceous sweat a deep purple color; it also works on bloody prints. GCV will visualize latent prints on the adhesive side of all tapes. Fluoresces at 525, 530, and 570nm (use red goggles); also at 485 and 450nm (use orange goggles). | May permanently stain some surfaces. |
DFO (1,8-Diazafluoren9-one) | A ninhydrin analog that reacts to the amino acids present in body proteins; is especially good for paper evidence. | Not recommended for spraying. Special conditions apply to photography. |
Glue fuming | Fumes from cyanoacrylate ester adhesives will develop latent prints by binding the proteins in the prints. The cyanoacrylate ester adhesive is heated in the presence of water to create the fumes. | The fumes from cyanoacrylate ester adhesives are irritating but nontoxic. |
Iodine | Fumes from iodine crystals develop latent prints on surfaces that are impractical for traditional dusting or have residues such as grease. The FBI has developed a method for spraying iodine solutions on large surfaces, such as walls. | Latent prints developed with iodine are visible for only a few hours. |
Ninhydrin | Develops latent prints on porous surfaces like paper by reacting with amino acids in latent print residue. In a fume hood, the specimens are submerged in the ninhydrin solution and then air-dried. | Avoid contact with the powder and solution form of ninhydrin. Any source of heat or spark should be avoided. |
Physical developer | A silver-based liquid reagent that reacts to lipids, fats, oils, and waxes present in the print residue. It is good for porous objects but should be the last process in the chemical sequence. | Numerous safety precautions are required for physical developers. Paper with a pH above 7 (like thermal fax paper) is not suitable for processing with a physical developer |
Small particle reagent (Molybdenum disulfide, MoS2) | A physical development technique in which small black particles adhere to the fatty substances left in print residue and is useful on many different surfaces. | Numerous safety precautions are required for small particle reagents. Developed prints should be photographed before lifting is attempted. |
Sudan black | Working best on glass, metal, or plastic materials that are greasy or sticky, Sudan black is a dye that stains the fatty components of sebaceous secretions. Sudan black also works well on the inside of latex gloves. | Stains many surfaces. Should not be used on porous or absorbent surfaces. |
Vacuum metal deposition | This is reported to be the most effective technique for most smooth, nonporous surfaces. The process evaporates gold or zinc in a vacuum chamber that coats the specimen surface with a microscopic layer of metal. | The equipment is expensive. |
Three Main Types of Lasers are used to detect fingerprints:
Argon Laser
Copper Vapor Laser
Neodymium-yttrium/arsenide/gallium (Nd:YAG) Laser
Three Classes of Fingerprints
Loops – have one or more ridges entering from one side of the print, curving back on themselves, and exiting the fingertip on the same side.
Ulnar Loop – the loop enters and exits on the side of the finger toward the little finger.
Radial Loop – the loop enters and exits on the side toward the thumb.
Type Lines – two diverging ridges that surround the loops.
Delta – point of divergence.
Core – central portion of the loop.
Arches – the rarest; these are either plain arch— with ridges entering one side of the finger, gradually rising to a rounded peak, and exiting the other side, or tented arch— which are arches with a pronounced, sharp peak.
Arches do not have type lines, cores, or deltas.
Whorls – subdivided into plain whorl, central pocket loop, double loops, and accidental.
Classification
The modern system of fingerprint classification is based on Henry’s original design, which could process a maximum of 100,000 sets of prints, with modifications by the FBI to allow for the huge number of entries that have accumulated over the years.
Values for Fingers in the Henry Classification System
Right thumb, right index | 16 |
|---|---|
Right middle, right ring | 8 |
Right little, left thumb | 4 |
Left index, left middle | 2 |
Left ring, left little | 1 |
All arches are considered “nonnumerical” patterns and are given a value of zero. Whorls are given values depending on which finger they appear.
How long do friction ridge prints last?
Plastic prints will last as long as the impressed material remains structurally intact.
Prints left in some medium, such as blood or dust, are quite fragile and do not last very long.
Latent prints, however, if in the proper environments, can last for years.
Elimination Prints
Obtaining known samples for elimination purposes can be of great assistance to forensic scientists.
These samples may not only eliminate individuals from an investigation’s focus but also demonstrate a proper scientific mindset through a comprehensive series of comparisons.
If these elimination knowns are incorporated into a trial presentation, they can create confidence in the mind of the trier-of-fact that not only do the defendant’s known prints match but also the other potential subjects’ prints do not match.
19.3: Automated Fingerprint Identification Systems
Automated Fingerprint Identification Systems (AFIS) – computerized databases of digitized fingerprints that are searchable through software—essentially, a computer and a scanner hooked to a network-type server computer.
Integrated Automated Fingerprint Identification Systems (IAFIS) – newer automated fingerprint system.
It can digitally capture latent print and 10-print images and then:
enhance an image to improve its quality;
compare crime scene fingerprints against known 10-print records retrieved from the database;
search crime scene fingerprints against known fingerprints when no suspects have been developed; and
automatically search the prints of an arrestee against a database of unsolved cases.
The Universal Latent Workstation – the first in a new generation of interoperable fingerprint workstations.
The Workstation is part of that program and it assists agencies and manufacturers understand and develop the concept of “encode once and search anywhere.”
19.4: Identification
Level 1 detail
Includes the general ridge flow and pattern configuration. It is not sufficient for individualization but can exclude an individual.
It may include information enabling orientation, core and delta location, and distinction of finger versus palm.
Level 2 detail
Includes formations, defined as ridge endings, bifurcations, dots, or combinations of these features.
It enables individualization.
Level 3 detail
Includes all attributes of a ridge, such as a ridge path deviation, width, shape, pores, edge contour, incipient ridges, breaks, creases, scars, and other permanent minutiae.
It obviously can lead to individualization as well and, it has been argued, when fingerprint examiners look at a print, they automatically take Level 3 detail into account.