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1 Forensic Fingerprints CHE 113 Forensic Science Copyright 2004, James T. Spencer.

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Presentation on theme: "1 Forensic Fingerprints CHE 113 Forensic Science Copyright 2004, James T. Spencer."— Presentation transcript:

1 1 Forensic Fingerprints CHE 113 Forensic Science Copyright 2004, James T. Spencer

2 2 Forensic Fingerprints 1000 BCE; archaeological evidence of ancient Chinese and Babylonian civilizations using fingerprints to sign legal documents. Early 1880's - William Herschel, Chief Administrative Officer of Bengal used thumb impressions to identify workers Dr Henry Faulds, an English physician working in Tokyo, published a letter in the journal Nature suggesting the use of fingerprints for identification purposes.

3 After some years of research the English scientist Sir Francis Galton published a book entitled Finger Prints in which was laid out a method of classification of fingerprints Indian Police officer Sir Edward Henry proposed a modified classification system which was adopted by Scotland Yard in 1901 and is still the basis of the systems used in most English speaking countries First official use of fingerprints in the USA by the New York City Civil Service Commission National fingerprint file set up in America by the FBI. 3

4 4 Fingerprints Fingerprints form by contact of friction ridges on hands, feet, or lips with an object (called 'friction' ridges because of their biological function to assist in our ability to grasp and hold onto objects - approximately 2,700 ridge "units" per square inch of friction skin). Pore openings present on surface of the friction ridges. Fingerprints are formed underneath the skin in the dermal papilae. As long as that layer of papilae is there, fingerprints will always come back, even after scarring or burning. Prints are left because a body is constantly secreting water, oils, etc. through pores.

5 5 Forensic Fingerprints Your fingerprint patterns are hereditary. They are formed before a person is born. They are unique and they never change. Gloves don't necessarily stop fingerprints. Prints can be left through surgical gloves. Gloves can also be turned inside out to yield fingerprints from the inside surfaces. Leather gloves leave prints that is unique to that glove and no other - leather comes from cow skin, sim.to human skin). Even cloth gloves, such as mittens, can leave a distinctive print that can be traced back to the mitten that made it. Latent Leather Glove Print Ref. Leather Glove Print

6 6 Fingerprint Basics A fingerprint is an individual characteristic. –Not the shape of the print that is individual, but rather the number, location and shape of specific ridge characteristics (also known as minutiae). –Most courts require matched minutiae for a positive match. A fingerprint will remain unchanged during an individual's lifetime. Fingerprints have general ridge patterns that permit them to be systematically classified.

7 7 Forensic Fingerprints Three basic fingerprint patterns: Loops, Arches and Whorls. Arches; 5 % population Loops; % Loops; % Whorls; % Whorls; % People of African ancestry tend to have frequent arches. People of European background have frequent loops. People of Asians/Oriental ancestry tend to have a fairly high frequency of whorls.

8 8 Fingerprints Within these patterns are minutia points - about thirty different types of minutiae points, and no two people have the same types of minutiae in the same number in the same places on their fingertips.

9 9 Loops 1 or more ridges entering from the side of the print, recurving and exiting from the same side. Opens toward little finger its ulnar and toward thumb it’s radial. Pattern area surrounding the loop is a type line. Delta surrounded by type lines. All loops have at least 1 delta.

10 10 Types of Arches and Whorls Arches Whorls

11 11 Forensic Fingerprints

12 12 Classification Primary Classification: –Henry (FBI) System - all prints fall into one of 1024 groups Pair up fingers on hands Determine whorls (list numerically) 10 finger system Automated Fingerprint Ident. Systems –Uses automated scanning devices.

13 13 Similar Types Lip Prints (glasses, cigarettes, napkins, etc.). Ear Prints (windows, doors and walls).

14 14 Types of Prints Latent Prints - invisible to the naked eye and must be developed to see. Visible Prints Plastic Prints - impressions of fingerprints in soft media (soap, wax, etc.) Fingerprint in putty common in burglaries.

15 15 Visualizing Fingerprints Most important method of detecting latent prints is to dust using a fine powder that adheres to the traces of oil and sweat. –Aluminum dust, which is grey and highly visible on dark and mirrored surfaces. –Carbon black for white surfaces. –Luminescent powders which fluoresce under ultraviolet light. –Magnetic Powders. –Other Colors are available. Dusting is suitable for hard and/or non-absorbent surfaces, for porous surfaces like paper or cloth another approach is needed.

16 16 Dusting Carbon, Metal, Magnetic Powders On Styrofoam

17 17 Luminescence Excitation of a molecule can happen in several ways including absorption of light or as a result of a chemical reaction. An excited molecule will lose energy with the electron falling back down the energy staircase to the ground state. For some molecules the excess energy is lost in the form of light, it is this process that is known as luminescence.

18 18 Luminescence A common application of luminescence is washing powder that contains optical brightener. The optical brightener is a fluorescent dye that shows a blue luminescence when excited by the ultraviolet radiation present in sunlight. Luminescence is used forensically to detect fingerprints, it also found application in de-bunking the fake Hitler diaries.

19 19 Luminescence Some components of sweat are luminescent and fluoresce when illuminated with lasers. Also, fluorescent dyes can be employed that do not require laser excitation.

20 20 Visualizing Fingerprints Dusting is suitable for hard and/or non-absorbent surfaces but for porous surfaces like paper or cloth chemical treatments are employed. –iodine fuming –ninhydrin –superglue fuming

21 21 Visualizing Prints Iodine - Iodine sublimes at room temperature. If an object is placed in a chamber with crystals of iodine placed in it, any fingerprints on the object will appear as brownish prints. The iodine is believed to dissolve in the skin oils that make up the print (temporary and will fade). Superglue - Cyanoacrylate ester. When vapors come into contact with fingerprints the molecules of the cyanoacrylate attach to the print and polymerize. The visible prints produced are white, but are often treated with a fluorescent dye to improve visibility.

22 22 Ninhydrin Method Colorless compound reacts with amino acids in sweat to form a colored compound. NinhydrinRuhemann’s Purple

23 23 Preserving Prints Photography (analog and digital imaging) Lifting with tape (or similar)

24 24 AFIS Law enforcement agencies, such as the FBI and the Scotland Yard, have built up vast collections of fingerprints. A fingerprint is first classified and compared with filed prints to try and establish a match, and therefore to identify a possible suspect. This process has been automated using automated fingerprint identification systems (AFIS).


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