Presentation on theme: "Forensic Fingerprints"— Presentation transcript:
1Forensic Fingerprints CHE 113 Forensic ScienceCopyright 2004, James T. Spencer
2Forensic 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.
3After 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.
4FingerprintsFingerprints 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.
5Forensic Fingerprints Latent Leather Glove PrintForensic FingerprintsYour 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.Ref. Leather Glove Print
6Fingerprint 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.
7Forensic Fingerprints Three basic fingerprint patterns: Loops, Arches and Whorls.Arches; 5 % populationLoops; % 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.
8FingerprintsWithin 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.
9Loops1 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.
12Classification Primary Classification: Henry (FBI) System - all prints fall into one of 1024 groupsPair up fingers on handsDetermine whorls (list numerically)10 finger systemAutomated Fingerprint Ident. SystemsUses automated scanning devices.
13Similar Types Lip Prints (glasses, cigarettes, napkins, etc.). Ear Prints (windows, doors and walls).
14Types of PrintsLatent Prints - invisible to the naked eye and must be developed to see.Visible PrintsPlastic Prints - impressions of fingerprints in soft media (soap, wax, etc.)Fingerprint in putty common in burglaries.
15Visualizing 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.
16DustingCarbon, Metal, Magnetic PowdersOn Styrofoam
17LuminescenceExcitation 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.
18LuminescenceA 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.
19LuminescenceSome components of sweat are luminescent and fluoresce when illuminated with lasers. Also, fluorescent dyes can be employed that do not require laser excitation.
20Visualizing Fingerprints Dusting is suitable for hard and/or non-absorbent surfaces but for porous surfaces like paper or cloth chemical treatments are employed.iodine fumingninhydrinsuperglue fuming
21Visualizing PrintsIodine - 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.
22Ninhydrin MethodColorless compound reacts with amino acids in sweat to form a colored compound.Ninhydrin Ruhemann’s Purple
23Preserving Prints Photography (analog and digital imaging) Lifting with tape (or similar)
24AFISLaw 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).