Transcript Document
Fingerprint Processing and Photography Professor Mike Wiehe Goals Students will receive a brief background about latent prints Traditional latent print recovery techniques will be discussed Students will learn about new chemical processes utilized today 2 A fingerprint is the impression made by the papillary ridges on the ends of the fingers and thumbs. Fingerprints afford an infallible means of personal identification, because the ridge arrangement on every finger of every human being is unique and does not alter with growth or age. 3 Ridges Each ridge of the epidermis (outer skin) is dotted with sweat pores for its entire length and is anchored to the dermis (inner skin) by a double row of peglike protuberances, or papillae. Injuries such as superficial burns, abrasions, or cuts do not affect the ridge structure or alter the dermal papillae, and the original pattern is duplicated in any new skin that grows. An injury that destroys the dermal papillae, however, will permanently obliterate the ridges. 4 Latent Fingerprinting Involves locating, preserving, and identifying impressions left by a culprit in the course of committing a crime. In latent fingerprints, the ridge structure is reproduced not in ink on a card but on an object in sweat, oily secretions, or other substances naturally present on the offender's fingers. Most latent prints are colorless and must therefore be "developed," or made visible, before they can be preserved and compared. 5 Latent Fingerprinting This is done by brushing them with various powders containing chalk or lampblack combined with other agents. The latent impressions are preserved as evidence either by photography or by lifting powdered prints on the adhesive surfaces of tape. 6 Three Kinds of Crime Scene Prints LATENT PRINT (hidden print) is a misnomer but often used inclusively. There are actually three kinds of crime scene prints. These are: 1. VISIBLE PRINTS which are prints made by fingers touching a surface after the ridges have been in contact with a colored material such as blood, paint, grease, or ink. 2. PLASTIC PRINTS which are ridge impressions left on a soft material such as putty, wax, soap, or dust. 3. True LATENT PRINTS which are invisible print impressions caused by the perspiration on the ridges of one’s skin coming in contact with a surface and making an invisible impression on it. Perspiration contains water, salt, amino acids, or oils and easily allows impressions to be made. 7 Conditions Affecting The Quality Of Latent Prints The surface on which the print is deposited The nature of the material contaminating the fingerprint Any physical or occupational defects of the person making the print How the object on which the prints appear was handled The amount of the contamination 8 Methods Of Developing Latent Prints Traditional powders Fluorescent Powders Chemicals Cyanoacrylate of superglue fuming Visualization under: Laser Alternative light Ultraviolet illumination 9 Most Effective Techniques for the Detection of Fingerprints Surfaces • Visual Examination All • Powders Smooth • Ninhydrin Paper, Cardboard, Wood etc • Sticky-Side Powders Adhesive Tapes • Physical Developer Wet paper • Fluorescence Various • Superglue + Fluorescence Polythene, Plastic molding, etc • Amido Black Fingerprints in Blood • Acid Yellow Fingerprints in Blood 10 Typical Exhibits from Crime Scenes For each surface there is usually one most productive technique which can be used on less important cases to save time 11 Typical Exhibits from Crime Scenes Superglue + Basic Yellow 40 Sudan Black Gentian Violet Small Particle Reagent Amido Black Ninhydrin For each surface there is usually one most productive technique which can be used on less important cases to save time 12 Powders - Can be effective on some surfaces but must use best powders Synthetic fibre, animal hair and glass fibre brushes in use Hundreds of types of powder available 13 Home Office Test Programme Assessment of the effectiveness of different powders and brushes on typical surface Using 20 to 30 donors and investigating performance on different types of surface over varying periods of time 14 Ninhydrin It was not until the mid 1950's that it was discovered that ninhydrin could be used to develop latent prints on porous surfaces. When ninhydrin comes into contact withamino acids in fingerprint residue, the reaction yields a red to purple print. Effective on virtually any porous surface, ninhyrdin is most appropriate for paper. 15 Ninhydrin 16 Ninhydrin Used On Bloody Shoe Print BEFORE AFTER 17 Use of Amino Acid Reagents at Crime Scenes on Wallpaper 18 Amido Black Aqueous Amido Black is a protein dye solution sensitive to the protiens in blood and other substances. It will not react with the typical proteins found in latent prints. Applied to non-porous materials such as plastic, glass or metal. It is a corrosive chemical, recommended to do presumptive blood test and DNA collection prior to application Photographs easily on light surfaces, utilize a forensic light source if located on a dark surface. 19 Amido Black 20 Acid Yellow 7 Acid Yellow 7 stain is one of the newer and more effective fluorescent stains used to enhance bloody footwear and fingerprint impressions on nonporous surfaces. Staining reveals a yellowish colored print which fluoresces under blue-green light (400-490 nm). When lifted with a white gelatin lifter the impression will often reveal enhanced fluorescence. 21 Fingerprints in Blood Acid Yellow 7 Bloody Fingerprint on Glass Bottle 22 Superglue Chamber for Fingerprints on Plastics Enhanced with fluorescent dyes Treatment Chamber The fingerprint deposit initiates the growth of fibrous deposit from ethyl cyanoacrylate vapor under conditions of high humidity; this is visible as a white deposit which may be enhanced with fluorescent dyes Developed Fingerprint 23 Making Fingerprints Fluoresce Chemically developed prints can sometimes be difficult to see and photograph A number of fluorescent reagents have been developed for the visualisation of fingerprints Some dyes may be used to enhance chemically developed fingerprints 24 High Intensity Light Sources Crimescopes and Lumalites use very similar or identical arc lamps to locate latent prints 25 A Solid State 532 nm Laser in Use 26 Alternate Light Source Accessories 27 Iodine Fuming Iodine crystals give off vapors that adsorb physically to the oil and fat substances of a fingerprint Use on porous and non-porous surfaces with fresh prints Developed prints are not fixed and need to be documented 28 Physical Developer Physical developer is a reagent that reacts with the lipids, fats, and oils, which are present in fingerprint residues Typically used after Ninhyrdrin and the forensic light source Photograph after each step 29 Specific Reaction - Catalysis/Initiation Fingerprint Deposits Developed with ‘Physical Developer’ Latent fingerprint on paper initiates deposition of silver from a surfactant stabilised silver nitrate solution Will even detect fingerprints on paper soaked in water for weeks 30 Physical Developer Processing 31 Small Particle Reagent It is a physical development technique where small black particles adhere to the fatty substances left in fingerprint residue Most well known for its ability to develop latent prints on wet surfaces, such as vehicles wet with rain Can spray it on a surface or dip an object in it Photograph any latent prints then dried prints can be lifted using traditional methods 32 Small Particle Reagent 33 Sequential Processing • There is a large variation in the chemical constituents of fingerprints from different people • There is also a large variation in the amount of latent fingerprint deposit between different people The deposit from the same person also varies from day to day and hour to hour • • • • Using one technique after another can therefore produce additional fingerprints The processes must be used in the correct sequence Different surfaces require different sequences of process 34 Sequential Processing • • Different types of surface require different treatment sequences Use of one process after another can double numbers of developed fingerprints 35 Typical Police Fingerprint Laboratory 36