Fundamental Principles ofFingerprintingSince, Galtons time, and as a result of hisefforts, fingerprints have become anintegral part of policing and forensicscience. The principal reason for this is thatfingerprints constitute a unique andunchanging means of personal identification.Fingerprint analysts have formulated threebasic principles of fingerprints thatencompass these notions of the uniquenessand stability of fingerprint identification.
Principle #1The Fingerprint is anIndividual Characteristic;No Two Fingers Have YetBeen Found to PossessIdentical RidgeCharacteristics
Principle #1The acceptance of fingerprint evidence by thecourts has always been predicated on theassumption that no two individuals haveidentical fingerprints.The probability for the existence of twoidentical fingerprint patterns in the worldspopulation is extremely small.
Principle #1Not only is this principle supported bytheoretical calculations, but just as important,it is verified by the millions of individuals whohave had their prints classified during the past110 years - no two have ever been found to beidentical. The FBI has nearly 50 millionfingerprint records in its computer databaseand has yet to find an identical imagebelonging to two different people.
Principle #1The individuality of a fingerprint is notdetermined by its general shape or patternbut by a careful study of its ridgecharacteristics (also known as minutiae).The identity, number, and relative location ofcharacteristics impart individuality to afingerprint.
Principle #1If prints are to match, theymust reveal characteristicsthat not only are identical,but have the same relativelocation to one another in aprint. In a judicialproceeding, a point-by-pointcomparison must bedemonstrated by the expert,using charts.
Principle #1An expert can easily comparethe characteristics of thecomplete fingerprint; theaverage fingerprint has asmany as 150 individualridge characteristics. Mostprints recovered at crimescenes, however, are onlypartial prints, showing onlya segment of the entireprint.
Principle #1Experts have debated for years about howmany ridge comparisons are necessary toidentify two fingerprints as the same.It has been suggested that between 8 and 16are sufficient to meet the criteria forindividuality.
Principle #1In 1973, the International Association forIdentification, after a three-year study ofthis question, concluded that "no valid basisexists for requiring a predeterminedminimum number of friction ridgecharacteristics which must be present in twoimpressions in order to establish positiveidentification." Hence, the finaldetermination must be based on theexperience and knowledge of the expert.
Principle #2A Fingerprint RemainsUnchanged During anIndividuals Lifetime
Principle #2Fingerprints are a reproduction of friction skinridges found on the palm side of the fingersand thumbs. Similar friction skin can alsobe found on the surface of the palms andsoles of the feet. Apparently, these skinsurfaces have been designed by nature toprovide our bodies with a firmer grasp and aresistance to slippage.
Principle #2A visual inspection offriction skin revealsa series of linescorresponding tohills (ridges) andvalleys (grooves).The shape and formof the skin ridges arewhat one sees as theblack lines of aninked fingerprintimpression.
Principle #2Skin is composed of layers ofcells. Those nearest thesurface make up the outerportion of the skin known asthe epidermis, and the innerskin is known as the dermis.A cross section of skin revealsa boundary of cellsseparating the epidermis anddermis. The shape of thisboundary, made up of dermalpapillae, determines theform and pattern of theridges on the surface of the
Principle #2Each skin ridge is populated by asingle row of pores that arethe openings for ducts leadingfrom the sweat glands.Through these pores,perspiration is discharged anddeposited on the surface ofthe skin. Onced the fingertouches a surface,perspiration, along with oilsthat may have been picked upby touching the hairy portionsof the body, is transferredonto that surface, therebyleaving an impression of thefingers ridge pattern.Prints deposited in thismanner are invisible to theeye and are commonlyreferred to as latentfingerprints.
Principle #2Although it is impossible to change onesfingerprints, come criminals have tried toobscure them. If an injury reaches deeplyenough into the skin and damages thedermal papillae, a permanent scar forms.However, for this to happen, suck a wouldnwould have to penetrate 1 to 2 millimetersbeneath the skins surface. Indeed, effortsat intentionally scarring the skin can only beself defeating.
Principle #2Perhaps the most publicizedattempt at obliteration wasthat of the notoriousgangster John Dillinger, whotried to destroy his ownfingerprints by applying acorrosive acid to them.Prints taken at the morgueafter he was shot to deathcompared with fingerprintsrecorded at the time of aprevious arrest, proved hisefforts had been fruitless.
Principle #3Fingerprints HaveGeneral RidgePatterns That PermitThem to BeSystematically
Principle #3All fingerprints are divided into three classeson the basis of their general pattern: loops,whorls, and arches. Sixty to 65 percent ofthe population have loops, 30 to 35 percenthave whorls, and about 5 percent havearches. These three classed form the basisfor all ten-finger classification systemspresently in use.
Principle #3: LoopsA loop must have one ormore ridges enteringfrom one side of theprint, recurving andexiting from the sameside. If the loop openstoward the little finger,it is called an ulnar loop;if it opens toward thethumb, it is a radialloop.
Principle #3: LoopsThe pattern area of theloop is surrounded bytwo diverging ridgesknown as type lines.The ridge point at ornearest the type-linedivergence andlocated at or directlyin front of the point ofdivergence is known asthe delta.
Principle #3: LoopsTo many, a fingerprint deltaresembles the siltformation that builds upas a river flows in theentrance of a lake - hencethe analogy to thegeological formationknown as a delta. Allloops must have onedelta. The core, as thename suggests, is theapproximate center of thepattern.
Principle #3: WhorlsWhorls are divided into four distict groups.Plain whorls, central pocket loop, doubleloop, and accidental.All whorl patternsmust have type linesand at least twodeltas.
Principle #3: WhorlsA plain whorl and a central pocket loop haveat least one ridge that makes a completecircuit. This ridge may be in the form of aspiral, oval, or any variant of a circle. If animaginary line drawn between the twodeltas contained within these two patternstouches any one of the spiral ridges, thepattern is a plain whorl. If no such ridge istouched, the pattern is a central pocketloop.
Principle #3: WhorlsImaginary line drawn between two deltas
Principle #3: WhorlsAs the name implies, the double loop is madeup of two loops combined into onefingerprint. Any whorl classified as anaccidental either contains two or morepatterns (not including the plain arch)or is apattern not covered by other categories.Hence, an accidental may consist of acombination loop and plain whorl or loopand tented arch.
Principle #3: ArchesArches, the least common of the three generalpatterns, are subdivided into two distinctgroups: plain arches and tented arches.
Principle #3: ArchesThe plain arch is the simplest of all fingerprintpatterns. It is formed by ridges entering fromone side of the print and exiting on theopposite side. Generally, these ridges tend torise in the center of the pattern, forming awavelike pattern.The tented arch is similar to the plain archexcept that instead of rising smoothly at thecenter, there is a sharp upthrust or spike, orthe ridges meet at an angle that is less than 90degrees. Arches do not have type lines,deltas, or cores.
Fingerprint Review to this Point!1. Fingerprints are a reproduction of friction skinridges found on the palm side of the fingers andthumbs.2. The basic principles underlying the use offingerprints in criminal investigation are:a.) A fingerprint is an individual characteristicbecause no two fingers have yet been found topossess identical ridge characteristicsb.) a fingerprint remains unchanged during anindividuals lifetimec.) fingerprints have general ridge patterns thatpermit them to be systematically classified
Fingerprint Review to this Point!3. All fingerprints are divided into threeclasses on the basis of their general pattern:Loops, Whorls, and Arches.4. The individuality of a fingerprint isdetermined not by its general shape orpattern, but by a careful study of its ridgecharacteristics. The expert mustdemonstrate a point-by-point comparison inorder to prove the identity of an individual.
Classification of FingerprintsThe original Henry system, as adopted byScotland Yard in 1901, converted ridgepatterns of all ten fingers into a series ofletters and numbers arranged in the form ofa fraction. However, the system as it wasoriginally designed could accommodate filesof only up to 100,000 sets of prints. Thus,as collections grew in size, it becamenecessary to expand the capacity of theclassification system.
Classification of FingerprintsIn the United States, the FBI, faced with theproblem of filing ever-increasing numbers ofprints, expanded its classification capacityby modifying and extending the originalHenry system. These modifications arecollectively known as the FBI system and areused by most agencies in the United Statestoday. Although we will not discuss all ofthe different divisions of the FBI system, adescription of just one part, the primaryclassification, will provide interesting insightinto the process of fingerprint classification.
Classification of FingerprintsThe primary classification is part of theoriginal Henry system and provides the firstclassification step in the FBI system. Usingthis classification alone, all of thefingerprint cards in the world could bedivided amount 1,024 groups. The first stepin obtaining the primary classification is topair up fingers, placing one finger in thenumerator and one finger in thedenominator of a fraction.
Primary Classification Using FBISystemThe fingers are paired in the following sequence:R. Index R.Ring L. Thumb L. Middle L. Little________ ________ ________ ________ _______R. Thumb R. Middle R. Little L. Index L. RingThe presence or absence of the whorl pattern is the basisfor determination of the primary classification.
Primary Classification Using FBISystemIf a whorl pattern is found on any finger of the firstpair, it is assigned a value of 16;on the second pair, a value of 8;on the third pair, a value of 4;on the fourth pair, a value of 2;on the last pair, a value of 1.Any finger with an arch or loop pattern is assigned avalue of 0. Approximately 25% of the populationfalls into the 1/1 category; that is, all theirfingers have either loops or arches.
Primary Classification Using FBISystemAfter values for all ten fingers are obtained inthis manner, they are totaled, and 1 isadded to both the numerator anddenominator. The fraction thus obtained isthe primary classification. For example, ifthe right index finger and right middlefingers are whorls, and all the others areloops, the primary classification is16 + 0 + 0 + 0 + 0 + 1 = 170 + 8 + 0 + 0 + 0 + 1 9
Primary Classification Using FBISystemA fingerprint classification system itself cannotunequivocally identify an individual; it merelyprovides the fingerprint examiner with a numberof candidates, all of whom have anindistinguishable set of prints in the systems file.The identification must always be made by a finalvisual comparison of the suspect prints and fileprints ridge characteristics; only these featurescan impart individuality to a fingerprint.Although ridge patterns impart classcharacteristics to the print, the type and positionof ridge characteristics give it its individual
Automated FingerprintIdentification SystemsThe Henry system and its subclassifications haveproven to be a cumbersome system for storing,retrieving, and searching for fingerprints,particularly as fingerprint collections grow insize. Nevertheless, until the emergence offingerprint computer technology, this manualapproach was the only viable method formaintaining fingerprint collections. Since 1970,technological advances have made possible theclassification and retrieval of fingerprints bycomputers.
Automated FingerprintIdentification SystemsIn 1999, the FBI initiated full operation of theIntegrated Automated FingerprintIdentification System (IAFIS), the largestAFIS in the United States, which links stateAFIS computers with the FBI database. Thisdatabase contains nearly 50 millionfingerprint records.
Automated FingerprintIdentification SystemsHow AFIS WorksThe heart of AFIS technology is the ability of a computerto scan and digitally encode fingerprints so that theycan be subject to high-speed computer processing.The AFIS uses automatic scanning devices that convertthe image of a fingerprint into digital minutiae thatcontain data showing ridges at their points oftermination (ridge endings) and the branching ofridges into two ridges (bifurcations). The relativeposition and orientation of the minutiae are alsodetermined, allowing the computer to store eachfingerprint in the form of a digitally recordedgeometric pattern.
Automated FingerprintIdentification SystemsThe computers search algorithm determinesthe degree of correlation between thelocation and relationship of the minutiae forboth the search and file prints. In thismanner, a computer can make thousands offingerprints comparisons in a second. Forexample, a set of ten fingerprints can besearched against a file of 500,000 ten-printsin 8/10s of a second.
Automated FingerprintIdentification SystemsThe stereotypical image of a booking officer rollinginked fingers onto a standard ten-print card forultimate transmission to a database has, for the mostpart, been replaced with digital-capture devices(livescan) that eliminate ink and paper. The livescancaptures the image on each finger and the palms asthey are lightly pressed against a glass platen. Theselivescan images can then be sent to the AFISdatabase electronically, so that within minutes thebooking agency can enter the fingerprint record intothe AFIS database and search the database forprevious entries of the same individual.
Considerations with AFISAFIS has fundamentally changed the way criminalinvestigators operate, allowing them to spendless time developing suspect lists and more timeinvestigating the suspects generated by thecomputer. However, investigators must becautioned against overreliance on a computer.Sometimes a latent print does not make a hitbecause of the poor quality of the file print. Toavoid these problems, investigators must stillprint all known suspects in a case and manuallysearch these prints against the crime sceneprints.
Methods of Detecting FingerprintsThere are three kinds of crime-scene prints:Visible prints: make by fingers touching asurface after the ridges have been incontact with a colored material such asblood, paint, grease or inkPlastic prints: ridge impressions left on asoft material such as putty, wax, soap, ordustLatent prints: impressions caused by thetransfer of body perspiration and/or oilspresent on finger ridges to the surface of anobject.
Locating FingerprintsLocating visible prints is easy since they arevisible. Locating latent prints is a littlemore tricky and requires the use oftechniques to make the print visible.Although the investigator can choose fromseveral methods for visualizing a latentprint, the choice depends on the type ofsurface being examined.
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