DEVELOPMENT OF LATENT PRINTS

COMPOSITION OF FINGERPRINTS Sweat

99.0-99.5 % water 0.5-1.0% solids

50% organic solids (mostly amino acids) 50% inorganic solids (NaCl and KCl)

Contaminants Bodily fluids (blood, saliva, nasal

secretions, semen, etc.) Oils and fats (sebum)

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THREE TYPES OF FINGERPRINT IMPRESSIONS Patent fingerprints – visible prints left on a

smooth surface when blood, ink, or some other liquid comes into contact with the hands and is then transferred to the surface

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THREE TYPES OF FINGERPRINT IMPRESSIONS(CONTINUED)

Plastic fingerprints – actual indentations left in some soft materials such as clay, putty, wax, or dust.

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THREE TYPES OF FINGERPRINT IMPRESSIONS(CONTINUED)

Latent fingerprints – fingerprints that are invisible to the naked eye and caused by the transfer of oils and other bodily secretions onto a surface. They can be made visible by various different methods

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FINGERPRINT POWDERS Applied lightly to a

nonabsorbent surface with a soft brush.

They readily adhere to sweat residues and/or deposits of body oils left on the surface.

Investigators need to prevent damaging the print when trying to develop it

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Did you know? Camel hair is the most common animal hair used to make fingerprint brushes. Now many brushes (like the one above) are made out of fiberglass.

FINGERPRINT POWDERS (CONTINUED)

Gray and black powders – the most common, chosen to make the best contrast with the surface

Fluorescent powders – used to photograph latent prints on multi-colored surfaces. They fluoresce under ultraviolet light.

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Magnetic powder – magnetic powders are applied with a magnetic brush Allows for very

delicate application of powders, decreasing chances of scratching prints with bristles

FINGERPRINT POWDERS (CONTINUED)

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THINGS TO CONSIDER ABOUT FINGERPRINT POWDERS… Fineness

The powder must be fine enough to show the detail of the fingerprint. Finer powders would be theoretically capable of displaying greater detail than coarser powders.

Adhesion The powder must display the right level of adhesion, so that it will

adhere to the residue of the fingerprint (often oils) and not adhere to the rest of the surface where it would obscure the view of the print. When a powder coats a surface, this is known as 'painting'.

Sensitivity Sensitivity is related to adhesion, and is how well the powder

adheres to a surface. For example, aluminum flake is more sensitive than aluminum powder, but greater sensitivity is not always desirable. Color The fingerprint powder must be a suitable color for the surface in question.

Flow To a lesser extent, it is important that the powder can flow, and

does not 'cake' into a solid block, which would render it useless.9

FINGERPRINT CHEMICALS Ninhydrin – reacts with amino acids in

sweat to form purple-blue prints. A 0.6% solution (in ethanol) is sprayed onto porous surfaces such as paper.

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N

O

O

O

O

C

R

H

H2N COOO

O

OH

OH

Ninhydrin

amino acids in fingerprints

Ruhemann's Purple Complex

FINGERPRINT CHEMICALS (CONTINUED)

Physical Developer – silver nitrate-based liquid reagent used on porous surfaces. It is often used as the last resort because it destroys protein.

Cyanoacrylate (superglue) fuming – developed in 1982 by Japanese Police. It is used on a variety of materials not only to visualize latent prints, but also to semi-permanently affix them to the surface. Works best on nonporous surfaces. Can be developed further with powders or fluorescent dyes

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FINGERPRINT CHEMICALS (CONTINUED)

DFO (1,8-diazafluotrn-9-one) – newer replacement chemical for ninhydrin. It is 2.5 times more sensitive than ninhydrin.

Rhodamine 6G is a fluorescent dye that may be used after cyanoacrylate fuming to visualize latent prints under laser light.

Once fluorescent dyes are applied, fingerprints can then be visualized using an Alternate Light Source (ALS) in an effort to enhance ridges and minimize background interference

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FINGERPRINT CHEMICALS (CONTINUED)

Iodine fuming – one of the oldest latent print development methods. Solid iodine crystals sublimate and the vapor will react with fatty oils and some sweat residue. Iodine prints are not permanent and will begin to fade once the fuming process is stopped. Can be used on porous and nonporous surfaces

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FINGERPRINT CHEMICALS (CONTINUED)

Gentian violet (or crystal violet) – used for developing latent prints on the adhesive side of tape. An aqueous solution of crystal violet is sprayed directly onto the adhesive.

Wetwop is another solution developer that can be used on adhesive surfaces.

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Amido Black – protein dye stain that can develop faint bloody fingerprints on porous and nonporous surfaces. Blood must be swabbed prior to amido black application for any DNA analysis

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FINGERPRINT CHEMICALS (CONTINUED)

FINGERPRINT CHEMICALS (CONTINUED)

LCV (Leuco Crystal Violet) – a protein stain spray that can develop faint or invisible bloody fingerprints on non-porous surfaces

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LUMINOL A chemical that reacts with hemoglobin to

produce the phenomenon of chemiluminescence (same as fireflies!)

Can be sprayed where nothing is visible. Under UV light, blood or bodily fluids glow

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OTHER CHEMICAL DEVELOPERS… Sticky-side powder – paste made with powder

that is used after cyanoacrylate fuming and on the sticky side of tape

Basic Yellow 40 – another fluorescent technique for nonporous surfaces or post-cyanoacrylate fuming

DAB – Diaminobenzidine formula – another blood enhancement technique

Small particle reagent – useful on wet surfaces such as plastic bags or coated surfaces – adheres to the fatty deposits in fingerprints 19

PRESERVATION OF DEVELOPED LATENT PRINTS Photograph!! Covering the print to preserve it in its

entirety (if on a small object) Lifting the prints with adhesive tape and

placing the tape with prints on a card with labels

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FACTORS AFFECTING FINGERPRINTS Age – thinner epidermis, flattening of dermal

papillae, creases, etc. Fine ridge structure – less skin contact

leads to a spotty appearance. Stimuli – sweating can be due to warmth,

exertion, fever, drugs, anxiety, tension, pain, or spicy foods.

Occupational and medical condition – teaching, and other positions in which a person handles or shuffles papers, can cause fine ridge structure.

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FACTORS AFFECTING FINGERPRINTS (CONTINUED)

Transposal factors Receiving surface texture Contaminants on the hands Contaminants on the receiving

surface The manner of contact The amount of pressure

Environmental factors Temperature Humidity Handling

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TRENDS WITH FINGERPRINTS It is NOT possible to determine the age, sex or

race of an individual solely from their fingerprints. However:

Statistically in young adults, friction ridges of women are significantly finer than those of men.

Fine ridges may be found in the very young and the very old.

Manual labor tends to strengthen ridges. Women tend to perspire at a lower rate than

men. Sodium chloride (NaCl) is lower for women. Creases are more common in women's FPs. 23

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AFIS

Database of fingerprints taken from arrests and unknown fingerprints found at unsolved crime scenes

Investigators enter both known and unknown prints and identify the minutiae

When an unknown print is entered into AFIS, the minutiae are identified and the computer crosses them with known offenders

THE INVESTIGATOR MAKES THE LAST DECISION on a match

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RESOURCES UNT in partnership with TEA, Copyright ©. All rights

reserved Saferstein, Richard. Forensic Science: An Introduction.

New Jersey: Pearson Prentice Hall, 2008. Bertino, Anthony J. Forensic Science: Fundamentals

and Investigations. Mason, OH: South-Western Cengage Learning, 2009.

Fisher, Barry A.J. Techniques of Crime Scene Investigation. 7th ed. Boca Raton, FL: CRC Press, 2004.

Federal Bureau of Investigations http://www.fbi.gov/hq/lab/fsc/backissu/jan2001/lpu.pdf Investigation Discoveryhttp://investigation.discovery.com/videos/forensics-

videos/28

VIDEOS AFIShttp://www.youtube.com/watch?

v=ZKi1CKTRCQM&feature=related

SUPERGLUE FUMINGhttp://www.youtube.com/watch?v=FkcSkADVMIM

Gentian Violethttp://www.youtube.com/watch?v=vBYYrwo8I6s

Ninhydrinhttp://www.youtube.com/watch?v=fF_v-MymoOk 29