FingerprintsFingerprints

OutlineOutline

Individuality of FingerprintsIndividuality of Fingerprints What are fingerprints?What are fingerprints? Classification of fingerprint patternsClassification of fingerprint patterns AFISAFIS Methods of detecting latent fingerprintsMethods of detecting latent fingerprints

Individuality of FingerprintsIndividuality of Fingerprints

Started collecting fingerprints around 1910 Started collecting fingerprints around 1910 (Civil Service)(Civil Service)

Millions of fingerprints have been classified Millions of fingerprints have been classified over past 95 years.over past 95 years.– No two are identical!No two are identical!– Estimated statistical probability of 1 in 64 billion Estimated statistical probability of 1 in 64 billion

that two people have identical fingerprintsthat two people have identical fingerprints

What are fingerprints?What are fingerprints? Combination of oils, salts, Combination of oils, salts,

proteins, perspiration left behind proteins, perspiration left behind by the friction ridges on by the friction ridges on fingertipsfingertips

Friction RidgeFriction Ridge– EpidermisEpidermis– DermisDermis– Dermal papillaeDermal papillae

Formed in the uterus Formed in the uterus Determines pattern of friction ridge Determines pattern of friction ridge Same shape for lifeSame shape for life

– Only grow in sizeOnly grow in size

ClassificationClassification LoopLoop

– Ulnar – opens toward pinkieUlnar – opens toward pinkie– Radial – opens toward thumbRadial – opens toward thumb

ArchArch– Plain Plain – TentedTented

WhorlWhorl– PlainPlain– Central pocket loopCentral pocket loop– Double loopDouble loop– AccidentalAccidental

Tented ArchTented Arch

Central Pocket Loop WhorlCentral Pocket Loop Whorl

Double Loop WhorlDouble Loop Whorl

Accidental WhorlAccidental Whorl

AFISAFIS

Automated Fingerprint Identification SystemAutomated Fingerprint Identification System– Converts a fingerprint image into digital minutiaeConverts a fingerprint image into digital minutiae

Relative locations of ridge endingsRelative locations of ridge endings And bifurcationsAnd bifurcations

– Thousands to millions of comparisons per secondThousands to millions of comparisons per second– Comparison must be verified by an expertComparison must be verified by an expert

How does AFIS compare prints?How does AFIS compare prints?

X

Y

Live Scan TechnologyLive Scan Technology

Fingers (and thumbs) rolled on a small Fingers (and thumbs) rolled on a small section of glasssection of glass

Pressure from ridges fed directly to computerPressure from ridges fed directly to computer Fingerprint appears on screen as finger is Fingerprint appears on screen as finger is

rolledrolled Keeps track of which finger is being rolled Keeps track of which finger is being rolled

based on combinationbased on combination No need to roll in ink then scan with scannerNo need to roll in ink then scan with scanner Coupled directly to AFISCoupled directly to AFIS

Types of Prints Types of Prints left at a Crime Sceneleft at a Crime Scene

VisibleVisible– Fingerprints left from fingers that have been in contact Fingerprints left from fingers that have been in contact

with colored material with colored material Blood, paint, grease, inkBlood, paint, grease, ink

PlasticPlastic– Ridge impressions left in soft materialRidge impressions left in soft material

Wax, putty, soap, dustWax, putty, soap, dust

LatentLatent– Invisible prints caused by the transfer of body Invisible prints caused by the transfer of body

perspiration or oilsperspiration or oils

Methods for detectingMethods for detectinglatent printslatent prints

PowdersPowders– Black, gray, fluorescent, etc.Black, gray, fluorescent, etc.– MagneticMagnetic

Chemical TreatmentChemical Treatment– NinhydrinNinhydrin– Silver NitrateSilver Nitrate– Super-GlueSuper-Glue

Combined with dyesCombined with dyes

Chemical TreatmentChemical Treatmentof Latent Printsof Latent Prints

NinhydrinNinhydrin– This chemical reacts with amino-acids on This chemical reacts with amino-acids on

proteinsproteins Turns dark blueTurns dark blue

– Quite useful on porous surfaces where dusting Quite useful on porous surfaces where dusting failsfails

– Can take up to 24 hours for latent print to Can take up to 24 hours for latent print to developdevelop Heat speeds this upHeat speeds this up

Chemical TreatmentChemical Treatmentof Latent Printsof Latent Prints

Silver NitrateSilver Nitrate– Perspiration contains salt (NaCl)Perspiration contains salt (NaCl)– Silver nitrate reacts with chloride to form silver chlorideSilver nitrate reacts with chloride to form silver chloride– Silver chloride can be converted to silver metal with UV Silver chloride can be converted to silver metal with UV

lamplamp

AgAg++ + Cl + Cl-- AgCl + UV AgCl + UV Ag (metal) Ag (metal)

Good for porous surfaces like paperGood for porous surfaces like paper

Chemical Treatment Chemical Treatment of Latent Printsof Latent Prints

Fuming Super GlueFuming Super Glue– Hang object in a sealed containerHang object in a sealed container

Covered fish tankCovered fish tank

– Heat a small amount of super glue in a dish on a Heat a small amount of super glue in a dish on a hot platehot plate Cyanoacrylate fumes react with components of latent Cyanoacrylate fumes react with components of latent

prints in 10-15 minutesprints in 10-15 minutes A white color is formed by this reactionA white color is formed by this reaction

– Good for large areasGood for large areas Like the inside of a carLike the inside of a car Difficult to remove prints once developed with this methodDifficult to remove prints once developed with this method Can treat super-glue print with fluorescent dyeCan treat super-glue print with fluorescent dye

Fuming ChamberFuming Chamber

Powders for latent printsPowders for latent prints

What color powder does one choose?What color powder does one choose?– Black, Gray, Red, etc.Black, Gray, Red, etc.

Powder color is chosen to contrast the color of the Powder color is chosen to contrast the color of the surfacesurface– Black surface, choose a gray powderBlack surface, choose a gray powder– Light surface, choose a black powderLight surface, choose a black powder– Multi-colored surface, fluorescent powderMulti-colored surface, fluorescent powder

How to apply powderHow to apply powderto visualize a latent printto visualize a latent print

Never touch the bristles of a fingerprint brushNever touch the bristles of a fingerprint brush Twirl or tap to remove powder from previous applicationTwirl or tap to remove powder from previous application Use a different brush for each powderUse a different brush for each powder Dusting powder in a shallow dishDusting powder in a shallow dish Dip tip of bristles in powderDip tip of bristles in powder

– Do not allow powder up in the center of bristlesDo not allow powder up in the center of bristles

Just graze the surface with a circular or sweeping motionJust graze the surface with a circular or sweeping motion

Once a print becomes visibleOnce a print becomes visible– Be careful not to dust with too much powderBe careful not to dust with too much powder– Continue as before until the direction of the ridges are Continue as before until the direction of the ridges are

visiblevisible– Follow the ridge direction with the brush motionFollow the ridge direction with the brush motion– If necessary, remove excess powder with clean brushIf necessary, remove excess powder with clean brush

How to apply powderHow to apply powderto visualize a latent printto visualize a latent print

How to Lift a PrintHow to Lift a Print

Peel off 6-7 cm of transparent bookbinding tapePeel off 6-7 cm of transparent bookbinding tape– Do not cutDo not cut

Cover the print by smoothing the tape over the print Cover the print by smoothing the tape over the print beginning at free end and working slowly over the print beginning at free end and working slowly over the print applying pressure with your fingerapplying pressure with your finger– Do not simply lay tape over printDo not simply lay tape over print

Air bubbles will destroy itAir bubbles will destroy it

Once tape covers printOnce tape covers print– Use roll as handle to peel tape from surface in one continuous Use roll as handle to peel tape from surface in one continuous

motionmotion Prevents distortion of printPrevents distortion of print

Smooth tape onto card of contrasting color as powderSmooth tape onto card of contrasting color as powder– Cut tapeCut tape