Fingerprinting Part II

Primary classification: The Henry This classification method was developed in 1899 as a way to classify 10 card fingerprint records. Allows for quick exclusion of candidates for a crime. The system assigns each finger a number based on where it is located (1 for thumb, 5 for pinky) AND assigns a point value to each finger. If a finger has a whorl, then it gets those points, if not, then it gets 0 points. These numbers are then plugged into an equation which gives the 10 card a fraction value between 1/1 to 32/32. This method has been influential in the development of AFIS.

The Henry Each finger is given a point value Using a 10 card print, examine each of the prints as to whether they are loops, arches, or whorls. If there is a whorl present, then those points are given for that finger.

Primary classification The presence of a whorl, earns the value for that finger. Insert the number point for each finger that has a whorl and substitute into this equation: The sum of the even finger values are calculated and placed in the numerator of the fraction. The sum of the odd finger values are placed in the denominator. This number is your primary classification number right right left left left index + ring + thumb + middle + little + 1 right right right left left thumb + middle + little + index + ring +1

Your turn:

Secondary classification Fingerprint minutiae are examined. Generally courts will accept 8-12 points of similarity on one print. This is considered an individual classification. This is what AFIS (Automated Fingerprint Identification Systems) does – it matches minutiae points. The latest technology creates a mathematical polygon based on X number of minutiae identified. This supposedly is less vulnerable to distortion than a typical examination for minutiae.

Types of Fingerprints There are 3 types of prints that investigators look for at crime scenes: Patent fingerprints—visible prints transferred onto smooth surfaces by blood or other liquids Plastic fingerprints—indentations left in soft materials such as clay or wax Latent fingerprints—made visible by dusting with powders or the use of chemicals 1 2 3

Developing Latent Prints Developing a latent print requires substances that interact with skin secretions that cause the print to stand out against its background. It may be necessary to attempt more than one technique, done in a particular order so as not to destroy the print. Powders—adhere to water and fatty deposits (from sweat and oil). Choose a color to contrast the background. Iodine—fumes react with oils and fats to produce a temporary yellow brown reaction.

Developing Latent Prints Ninhydrin—reacts with amino acids to produce a purple color. Silver nitrate—reacts with chloride to form silver chloride, a material which turns gray when exposed to light. Cyanoacrylate—“super glue” fumes react with water and other fingerprint constituents to form a hard, whitish deposit. In most labs lasers and alternative light sources can be used to view latent fingerprints. https://www.youtube.com/watch?v=v6D9JS972_4

Iodine fuming

Ninhydrin Fingerprint

Cyanoacrylate (superglue) **View movie clip from BHC 2 https://www.youtube.com/watch?v=R0e8WXkFA64

Other Prints Ears—shape, length and width Voice—electronic pulses measured on a spectrograph

Other Prints Lips—display several common patterns Short vertical lines Short horizontal lines Crosshatching Branching grooves

Other Prints Bite marks are unique and can be used to identify suspects. We will investigate this more in unit 10.

Other Prints The blood vessel patterns in the eye may be unique to individuals. They are used today for various security purposes.

Fingerprint Forensic FAQs Can fingerprints be erased? Only temporarily; they will grow back if removed with chemicals John Dillinger attempted to remove his fingerprints with acid, but they grew back as the skin healed/regenerated. Is fingerprint identification reliable? Yes, but analysts can make mistakes In 1995 as part of an experimental test, 156 fingerprint examiners were given several sets of prints to analyze. 1 in 5 made at least one false positive. Can computers perform matches in seconds? No, but the FBI’s Integrated Automated Fingerprint Identification System (IAFIS or AFIS) can provide a match in 2 hours. However prints are generally not compared out of state lines unless there is reason to believe that is necessary. (this can take longer).

Any questions?

Activity: Prepare a 10 card on your partner. https://www.youtube.com/watch?v=d7N-4UNAzsw