Introduction to Forensic Science

Fingerprints and Biometrics

Alphonse Bertillon

• (April 23, 1853—February 13, 1914) was a French law enforcement officer and biometrics researcher who created anthropometry, an identification system based on physical measurements.

• Anthropometry was the first scientific system police used to identify criminals. Until this time, criminals could only be identified based on eyewitness accounts, which are known to be unreliable.

Bertillon and the Mug Shot

• After the invention of photography, police began to keep "rogues' galleries," disorganized photographic collections of suspects and convicts. They needed a way to retrieve images and information quickly.

• In 1879, Alphonse Bertillon invented a method that combined detailed measurement and classification of unique features with frontal and profile photographs of suspects—and which recorded the information on standardized cards in orderly files.

Bertillon's system was based on five primary measurements• head length• head breadth• length of the middle

finger• the length of the left

foot• the length of the

"cubit" (the forearm from the elbow to the extremity of the middle finger).

Bertillon Card

Bertillon created an early database

• Bertillon’s system combined photography and measurement to create a record of unique identifiers that could be used to track suspects, inmates, and repeat offenders.

• Unique characteristics like tattoos and scars were also recorded.

• His system depended on a complicated filing method that cross-referenced a standardized set of identifying characteristics, making the information retrievable.

• The identification process was entirely independent of names and the final identification was confirmed by the photographs included on the individual's card.

Bertillon Files

The Case of Will West

Will West's Bertillon Measurements 178.5; 187.0; 91.2; 19.7; 15.8; 14.8; 6.6; 28.2; 12.3; 9.7

William West's Bertillon Measurements 177.5; 188.0; 91.3; 19.8; 15.9; 14.8; 6.5; 27.5; 12.2; 9.6; 50.3

Fingerprint History• 1880: Dr Henry Faulds published his first paper on

the subject in the scientific journal Nature in 1880. Returning to the UK in 1886, he offered the concept to the Metropolitan Police in London but it was dismissed.

• 1892: Sir Francis Galton published a detailed statistical model of fingerprint analysis and identification and encouraged its use in forensic science in his book Finger Prints.

• 1892: Juan Vucetich, an Argentine police officer who had been studying Galton pattern types for a year, made the first criminal fingerprint identification. He successfully proved Francisca Rojas guilty of murder after showing that the bloody fingerprint found at the crime scene was hers, and could only be hers.

Juan Vucetich’s Early Fingerprints

What Are Fingerprints?

• Friction ridges are found on skin of – palms of hands– palmar aspect of fingers – soles of feet– solar aspect of toes

• Designed by nature for firmer grip and resistance to slippage

Skin Structure

• Outer, surface layer of skin is epidermis

• The inner layer of skin is the dermis• Between these two are the dermal

papillae• Papillary pattern determines the

form and pattern of the friction ridges on skin surface

Perspiration and oils are secreted through glands in the

skin

Uses of Fingerprints

• Fingerprints collected at a crime scene, or on items of evidence from a crime, can be used to identify suspects, victims and other persons who touched a surface.

• Fingerprints can be used to identify a corpse

• Fingerprints can be used to identify people who might use aliases to disguise their illegal intent.

First Principal: Fingerprints are Unique

• Millions of prints taken over 90 years

• No two fingers have yet been found to have identical ridge characteristics (minutiae)

• Identical (monozygous) twins

– have same DNA

– have different fingerprints

Second Principal: Fingerprints are Unchanged through Life

• Friction ridge pattern of skin develops in utero (before birth)

• Pattern remains unchanged throughout life

Do fingerprints remain unchanged?

• Impossible to do, but there has never been a lack of trying– John Dillinger-corrosive acid

• To change the pattern requires obliteration of the dermal papillae (1- 2 mm deep)

• Attempts to destroy pattern causes disruption, irreversibly adding more detail!

Left middle fingerprint Left middle fingerprint

This permanent scar irreversibly changes the fingerprint. It starts near the core of the loop and passes to the right of the screen.

Third Principal: General Patterns allow systematic

classification• The 3 basic fingerprint patterns

– loops (60-65% of population of fingers)

– whorls (30-35% of fingers)– arches (5% of fingers)

•Once fingerprints are recorded, a system is required to describe and place them in logical order

•Different classification systems

•English-speaking countries use system created by Sir Edward Richard Henry.

•This system has been modified by the FBI in the USA.

ClassificationClassification

Fingers arranged in pairs:R Index R Ring L Thumb L Middle L Little & & & & &

R Thumb R Middle R Little L Index L Ring

Whorl pattern on either finger of pair, scored as 16 8 4 2 1

Expressed as fraction. 1 added to numerator & denominator

e.g. Whorls on R Index & R Middle fingers

16 + 0 + 0 + 0 + 0 + 1 = 17

0 + 8 + 0 + 0 + 0 + 1 9

25% population are 1/1

(no whorls)

Henry System of Classification

Three Categories of Fingerprints

• Plastic prints – Created when the fingers touch against some

material such as putty

• Patent or visible prints – Formed when the fingers are contaminated

with such things as ink or blood and touch a clean surface

• Latent/invisible prints – Left on a surface from the small amounts of

body oil and perspiration that are normally found on friction ridges

– Require enhancements to become visible

Fingerprints as Class Evidence

Biometrics

• The study of methods for uniquely recognizing humans based upon one or more intrinsic physical or behavioral traits.

http://en.wikipedia.org/wiki/Image:Biometrics_traits_classification.png

Evaluating Biometrics Characteristics

• Universality each person should have the characteristic

• Uniqueness is how well the biometric separates individually from another.

• Permanence measures how well a biometric resists aging.

• Collectability ease of acquisition for measurement.

• Performance accuracy, speed, and robustness of technology used.

• Acceptability degree of approval of a technology.

• Circumvention ease of use of a substitute.

http://en.wikipedia.org/wiki/Biometrics#Common_human_biometric_characteristics

Classification of minutiae

• Minutiae are basically ends and bifurcations of the ridge lines that comprise a fingerprint pattern.

• Valleys are the preferred choice to trace in algorithms.

Minutiae

Marked Minutiae

Fingerprint Matching Process

Biometric system operations

• Capture: a physical or behavioral sample is captured by the system during enrollment.

• Extraction: unique data is extracted from the sample and a mathematical template is created.

• Comparison: the mathematical code is then compared with a new sample.

• Match/Non-match: the system then decides if the features extracted from the new sample are a match or a non-match.

Matching the fingerprint

• Most automatic systems for fingerprint comparison are based on minutiae matching.

• The loop is the most common.

• The loop is easy to classify based on ridge counting and it constitutes 65% of all patterns.

Traditional Fingerprint Identification and Comparison

• In the past fingerprints taken from crime scenes were classified, filed and searched according to the Henry System

• Searching crime scene fingerprints against a Henry System file was labor-intensive

• Technological advancement since the 1970s have allowed the creation of an automated fingerprint identification process

Automated Fingerprint Identification System (AFIS)

• In the early 1970s, the FBI and the National Bureau of Standards conducted feasibility research for establishing an automated fingerprint identification process

• AFIS allows law enforcement agencies to conduct comparisons of applicant and suspect fingerprints with literally thousands or millions of file prints in a matter of minutes

Automated Fingerprint Identification System (AFIS)

• AFIS has two major duties– First is performing the functions of

classifying searching and matching prints– Second is the storage and retrieval of

fingerprints data• In July 1999, law enforcement agencies

began to have access to the FBI’S Integrated Automated Fingerprint Identification System (IAFIA), a national on-line fingerprint and criminal history database with identification and response capabilities

AFIS Fingerprint Comparison

• Latent prints can be searched against a file of 500,000 prints in one half hour

• The system produces a list of possibles called a candidate list

• Checked by a qualified fingerprint examiner

Automated Fingerprint Identification System (AFIS)

• The local police agency must have a live-scan fingerprint terminal. The agency may then:– Scan an arrestee's prints and mug shots– Electronically transmit the prints, mug

shots and personal information to their state's network for fingerprint checks

• The state agency then transmits the same information to the FBI fingerprint repository for matches

Fingerprints are not infallible

• Shirley McKie, a former policewoman was acquitted of perjury. She was accused of lying about a fingerprint at a murder trial. The case stemmed from what was allegedly Ms McKie’s thumb print, found at the scene of a murder. She had denied that the thumb print was hers, or that she had even been in the room where it was found.

• Expert witnesses backed the plea of innocence and she was acquitted by a jury.

• The Chief Inspector of Constabulary, Mr William Taylor, exonerated Ms McKie and concluded that the Scottish Criminal Records Office (SCRO) Fingerprint Bureau was “not fully effective and efficient”.

• Taylor concluded that there should be a move away from the current analysis system, which seeks to match 16 points of similarity between prints from a crime scene and a suspect. Also highlighted the need for improvements in training and backed a centralised fingerprint service in Scotland.

Brandon Mayfield and Madrid bombing

• Brandon Mayfield is an American lawyer identified as a participant in the Madrid bombing based on a fingerprint match.

• The FBI Latent Print Unit ran the print collected in Madrid and reported a match against one of 20 fingerprint candidates returned in a search response from their IAFIS—Integrated Automated Fingerprint Identification System.

• The FBI initially called the match "100 percent positive" and an "absolutely incontrovertible match".

Brandon Mayfield and Madrid bombing

• The Spanish National Police examiners concluded the prints did not match Mayfield, and after two weeks identified another man who matched.

• The FBI acknowledged the error, and a judge released Mayfield after two weeks in May 2004.

• In January of 2006, a U.S. Justice Department report was released which faulted the FBI for sloppy work but exonerated them of more serious allegations.

• The report found that misidentification was due to misapplication of methodology by the examiners involved: Mayfield is an American-born convert to Islam and his wife is an Egyptian immigrant, not factors that affect fingerprint search technology.

Validity of fingerprinting as an identification method

• Fingerprint examination is an applied science based upon the foundation of biological uniqueness, permanence, and empirical validation through observation.

• Reliability of fingerprint examination is supported by the theories of biological uniqueness and permanence, probability modeling, and empirical data gained through over one hundred years of operational experience.

SWGFAST• The mission of the Scientific Working Group on Friction

Ridge Analysis, Study and Technology (SWGFAST) is to establish consensus guidelines and standards for the forensic examination of fingerprints, palm prints and foot prints.

• SWGFAST, established in 1995, is one of several Scientific Working Groups (SWG).

• The Scientific Working Groups improve forensic science practices and build consensus amongst federal, state, and local forensic laboratories and practitioners.

• The SWGs are a focal point for discussion on key issues in various forensic science disciplines and develop guidelines and standards through consensus and general acceptance. These guidelines and standards are then published and are widely recognized by the forensic community, the courts, and the forensic laboratory accrediting bodies.

Collecting Fingerprint Data

• Fingerprint Data is much more common than DNA data and is used to solve more crimes.

• Fingerprint data can even be found years later on evidence and used to solve cold cases.

Conditions Affection Latent Print Quality

• 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 transfer

Fingerprinting Technology

• Powder Techniques– Used on non-absorbent surfaces– Tipped or softly brushed on

• Various types– Black powder (carbon)– Grey powder (Aluminium dust)– Magnetic-Sensitive Powder (Magnabrush)– Fluorescent Powder (seen in UV light)

• Powder is brushed on carefully• Excess is removed• Print lifted with broad adhesive

tape/pad• Transferred by sticking tape onto

card

Chemical Methods

• Iodine Fuming • Ninhydrin• DFO• Silver Nitrate• Physical developer• Super Glue Fuming

Iodine

• Oldest technique for latent prints• Iodine crystal sublimes in Fuming

Cabinet• Iodine reacts with fatty oils or

perspiration• Print fades rapidly• Fixed by spraying with starch

solution (blue)

Ninhydrin

• Ninhydrin (triketohydrindene hydrate)• For latent prints on paper & porous

surfaces• Easy to use & sensitive• Sprayed on• Prints appear 1-2 h • weak prints up to 48 h, hastened by

heat

Silver Nitrate

• For Porous surfaces• paper, wood, cloth, brass• Article sprayed, brushed or dipped• AgNO3 + NaCl --> AgCl + NaNO3• AgCl is photosensitive, turns dark

brown in daylight or UV• Blurs with time, recorded by

photography

• Silver nitrate-based liquid reagent• Useful on paper & porous surfaces• may work when other methods have

failed– useful on previously wetted paper

Superglue Fuming

• Cyanoacrylate ester (Super Glue)• Fuming by heat or NaOH in cabinet • Fuming wand for use at scene (inside

a car)• Non-porous surfaces• metal, tape, leather, plastic• White prints appear in a few hours

Fluorescence Techniques

• Argon-ion Lasers• Alternate Light Sources• Colored filters & goggles required• Natural fluorescence by components of

perspiration and blood• Fluorescent powders• Fluorescent dyes

– ninhydrin + ZnCl– Superglue + Rhodamine

Fluorescence can really work!

Before After

Alternate Light Source

Latent Print Development Methods

• Traditional powders• Fluorescent Powders• Chemicals• Cyanoacrylate of superglue fuming• Visualization under:

– Laser– Alternative light– Ultraviolet illumination

3-11

Locating Prints

• Crime Scene Technician

This technician is using powder to develop latent prints– Technicians often

wear protective equipment

– Several points can be seen (Courtesy Nassau County, New York, Police Department)

Superglue Fuming Chamber

• is used to process the inside and the outside of the car.

• is more efficient for processing larger objects.

(Courtesy Sirchie)

Biometrics

– Measurement– Comparison– Authentication

http://www.itl.nist.gov/div893/biometrics/

ID Proofing –Three Questions

• Is Joe Blow real person? Does a person named Joe Blow with the claimed attributes exist?—As a practical matter, if somebody lives for a

while under a name, that person exists

• Is the applicant that Joe Blow?• Can Joe Blow later repudiate his

registration?– Can Joe later say, “Look, you may have

registered somebody as Joe Blow, but it wasn’t me.”

Patriot Act Mandates

• Develop and certify technology standard to verify identity of foreign nationals applying for a visa– visa application at embassies and consulates– background check against FBI criminal

database and DHS databases and “watch lists”– ensure person has not received visa under a

different name• Verify identity of persons seeking to enter

the U.S.– verify that the person holding the travel

document is the same person to whom the document was issued

– airports, land border crossings, sea entry points

NIST Study Results

• The most accurate face systems: – 0.72 true accept rate @ 10-4 false accept rate – 0.90 true accept rate @ 10-2 false accept rate.

• The most accurate fingerprint system, using operational quality single fingerprints:– 0.994 true accept rate @ 10-4 false accept rate – 0.999 true accept rate @ 10-2 false accept rate

• More fingerprints (1 vs 2-10) are more accurate

• Image Quality is critical

Face Recognition

Every face has numerous, distinguishable landmarks, the different peaks and valleys that make up facial features.

These landmarks are defined as nodal points. Each human face has approximately 80 nodal points. Some of these are:

Distance between the eyes Width of the nose Depth of the eye sockets The shape of the cheekbones The length of the jaw line

These nodal points are measured creating a numerical code, called a faceprint, representing the face in the database.

Tattoo Statistics

• Rising popularity (Harris Poll, July 2003):• 16% of the adults in the US have at least one tattoo• The highest incidence was found among Americans

age 25 to 29 years (36%) and 30 to 39 years (28%)• People living in the West (20%) are more likely to

have tattoos• Democrats are more likely to have tattoos (18%) than

Republicans (14%) and Independents (12%)• Approximately equal percentages of males (16%) and

females (15%) have tattoos• Tattoos are getting bigger, more colorful and visible

Creating a Database

• Eight major tattoo classes: Human, Animal, Plant, Flag, Object, Abstract, Symbol, Other; 80 subcategories

• Scientists are developing automatic image based matching and retrieval of tattoo images

Tattoos and Identification