Friction Ridge Examination Notes

Friction Ridge Examination Introduction

Friction ridges are found on palms, soles, fingers, and toes. Friction ridge examination focuses on fingerprints, commonly found at crime scenes. Fingerprints are a leading identification marker in forensic science (Houck and Siegel, 2006) and are frequently used to identify, prosecute, and convict suspects. DPP v John Cash is a key case demonstrating the fingerprint identification process.

Historical Development of Fingerprinting Techniques

Fingerprinting is a cost-effective crime-solving mechanism. Police forces began using fingerprint identification around 110 years ago. The first US criminal conviction using fingerprint evidence was in Chicago in 1911 (Thomas Jennings case). In Ireland, the conviction of Patrick Pett and Michael Maher in 1914 relied on fingerprint expert Mr. Henry's crucial evidence.

Statutory Powers to Take Fingerprints

Section 6 of the Criminal Justice Act 1984 (as amended) and Section 100 of the Criminal Justice (Forensic Science and DNA Database) Act 2014 grant Gardai the power to take fingerprints and palm prints from arrested individuals for questioning or charging. This requires authorization from a Garda Sergeant (or higher rank, S.100) or a Garda Inspector (or higher rank, S.6). Obstructing Gardai in taking prints is an offense punishable by a fine or imprisonment (up to 12 months).

PRINTRAX Biometric Information System

Fingerprints taken by Gardai are scanned and uploaded to the PRINTRAX system. The system also contains questioned prints from crime scenes and elimination prints from forensic and police personnel. PRINTRAX replaced the older AFIS system, which had compatibility issues with other jurisdictions. Computerized systems have expedited fingerprint comparison, but a fingerprint expert must validate suspected matches and provide expert testimony in court.

Friction Ridge Prints

Friction ridge patterns are found on palms, soles, fingers, and toes of primates. These ridges evolved to enhance gripping. They begin forming during the 9th-10th week of fetal development in the dermal layer. Sweat glands and ducts form around week 14, and secondary friction ridges appear around week 16, fully developing by week 24. The friction ridge template is located between the dermal and epidermal layers. Friction ridges are permanently fixed during fetal gestation and only change due to scarring or trauma (Carlson, 2003).

Types of Friction Ridge Prints

Friction ridge prints can be patent (visible to the unaided eye) or latent (requiring assistance to be seen). Patent prints occur due to transferable material like blood or paint, or impressions on soft surfaces. Latent prints require visualization techniques to reveal sweat and oils (Houck and Siegel, 2006). Latent prints can last for years in the right environment.

Visualizing Latent Prints

Common visualization techniques include fingerprint powders (colored, fluorescent, or magnetic) brushed over suspected areas to create contrast. Fluorescent powders require specific wavelengths of light and special films. Glue fuming (using heated ‘superglue’ and water) binds to proteins in the fingerprint, which can then be dusted. Both patent and latent prints should be photographed before lifting. Fingerprint photographers need expertise in lighting, exposure, filters, and enhancement (Houck and Siegel, 2006).

Fingerprints at Crime Scenes

In burglaries, patent and latent prints are often found at entry points or on touched surfaces. After visualization and photography, prints are usually 'lifted' with clear tape and mounted on contrasting cards. In serious crimes, items with prints (e.g., doorknobs) may be removed for laboratory analysis to preserve the print (Houck and Siegel, 2006).

Classification of Fingerprints

Fingerprints are divided into loops, whorls, and arches (Houck and Siegel, 2006). Loops are most common (approximately 70%), followed by whorls (25%) and arches (5%) (Langford et al, 2019).

  • Loops: Have one or more ridges entering and exiting on the same side. Subdivided into ulnar loops (entering/exiting towards the little finger) and radial loops (entering/exiting towards the thumb). Loops have two diverging ridges called type lines and a delta (Houck and Siegel, 2006).

  • Whorls: Subdivided into plain whorl, central pocket loop, double loop, and accidental. All whorls have type lines and at least two deltas. Central pocket loops and plain whorls have a minimum of one continuous ridge (may be a circle, oval, ellipse, or spiral). Plain whorls are located between the two deltas, while central pocket loops are not. A double loop consists of two loops swirling around each other. An accidental whorl combines multiple patterns or doesn't fit other categories (Houck and Siegel, 2006).

  • Arches: The rarest pattern. Plain arches have ridges entering one side, rising to a rounded peak, and exiting the other side. Tented arches have a sharp peak. Arches lack type lines, cores, or deltas (Houck and Siegel, 2006).

Friction Ridge Analysis and Identification

Francis Galton pioneered the scientific study of fingerprints for identification, enabling their use in criminal cases. Fingerprint identification must be precise to convince a judge or jury. Galton estimated the probability of two people having identical fingerprints and established a classification system still in use (Houck and Siegel, 2006). Fingerprints possess unique characteristics called minutiae. Uniqueness is determined by the presence, kind, number, and arrangement of these characteristics.

Matching Fingerprints

When comparing a questioned print (crime scene) and a known print (suspect), a match is declared if there are enough significant minutiae in the known print that are also present in the questioned print, with no relevant differences. Comparing prints can be challenging when questioned prints are incomplete or smudged. The final identification decision relies on sufficient quality and quantity of Level 1, 2, and 3 friction ridge details (Houck and Siegel, 2008).

  • Level 1 Detail: Can exclude an individual but is not detailed enough for individualization.

  • Level 2 Detail: Sufficient for individualization due to unique print features.

  • Level 3 Detail: Includes all attributes of a friction ridge pattern, leading to individualization.

Points of Comparison vs. Holistic Approach

Each fingerprint feature is a 'point of comparison.' Some jurisdictions require a specific number of points for confirmation ('counting points'). Others favor a holistic approach, considering the entire friction ridge pattern. The International Association for Identification (1973) opposes a minimum number of characteristics. Critics of the holistic approach argue that it lacks objectivity. Doubts about the objectivity of fingerprint examination exist (U.S. v Llera Plaza, 2002).

Case Study: DPP v John Cash [2010] IESC 1

John Cash was charged with burglary. The case centered on three sets of fingerprints. Detective Garda Barry Walsh found finger marks (“Prints 2”) on glass at the burgled house. These matched “Prints 1,” an earlier set on record belonging to the accused. Garda Walsh arrested Cash based on this match. Cash’s fingerprints (“Prints 3”) were taken, and a fingerprint expert (Detective Garda Gannon) confirmed that Prints 2 and 3 were made by the same person.