Fingerprinting

Bertillon Method of ID

• A French police expert, Alphonse Bertillon, relied on a description of the subject, with precise body measurements.

• Skeletons were thought to be so diverse that no two people would have the same measurements.

• This system of ID became known as the Bertillon system and was practiced for over 20 years.

History of Fingerprinting

• Evidence exists that the Chinese used the fingerprint to sign legal documents as far back as three thousand years ago!

• However, it is not known whether the practice was for ceremonial purposes or for personal identification.

History of Fingerprinting

• It wasn’t until 1880 that Henry Fauld suggested that ridge patterns may be used for important identification of criminals.

• He noted that a thief left fingerprints at the crime scene on a white-washed wall. When compared with the suspect’s fingerprints, there were obvious differences.

• Finding the person who had fingerprints that matched resulted in the person confessing to the crime.

History of Fingerprinting

• Francis Galton was the first person to print a textbook on the subject of fingerprinting. (Finger Prints, 1892)

• He was the person who proposed three basic patterns of fingerprints:

• 1) loops

• 2) whorls

• 3) arches

History of Fingerprinting

• In the US, the first systematic and official use of fingerprints for personal identification was used by the New York City Civil Service Commission in 1901.

• In 1924, the fingerprint databases of the FBI and Leavenworth prison were merged to form the nucleus of the FBI records.

• The FBI currently has the largest database of fingerprint records in the world.

AFIS• The FBI database has over 50 million

fingerprint records. State AFIS records were linked to the FBI in 1999.

• Smaller, independent AFIS systems, like those of local police, often are not compatible with the FBI database due to software issues!

• AFIS searches for several minutiae characteristics. Correlation between the location and minutiae present are considered.

AFIS

• AFIS is not a replacement for an actual person…

• CSI myth- the computer does not narrow it down to 1 match. An actual person must search through possible matches to choose the best choice.

Principles of Fingerprints

• First principle: A fingerprint is an individual characteristic; No two fingers have yet been found to possess identical ridge characteristics.

• This principle is supported by theoretical calculations.

• The individuality is determined by a fingerprint’s ridge characteristics. The identity number and the location are what are unique.

Identification Criteria

• A given fingerprint may have as many as 150 individual ridge characteristics.

• However, there are usually only partial prints found at crime scenes.

• There has been much debate about how many ridges are necessary to declare an individual match.

• The consensus is that there is no minimum number because there has not been a comprehensive statistical study done to prove how many ridges are necessary to be considered a match.

Principles of Fingerprinting

• Second principle: A finger print will remain unchanged during an individual’s lifetime.

• Fingerprints are a reproduction of friction skin ridges found on palms to provide us with a firmer grasp and resistance to slippage.

• They resemble a series of lines that correspond to hills (ridges) with valleys (grooves) in between them.

Layers of the Skin

• The outer portion of skin is called the epidermis.

• The inner portion of the skin is called the dermis.

• The layer in between is made up of dermal papillae, which determine the ridge characteristics.

Dermal Papillae

• Once the dermal papillae develop in the fetus, the ridge patterns will remain unchanged throughout life except to become larger due to growth.

Latent Prints

• Prints that are invisible to the eye are commonly referred to as latent prints.

• These prints are formed by perspiration and oils that is discharged and deposited on the surface of the skin.

• Once the finger touches a surface, the ridge patterns are transferred to that surface, leaving behind a fingerprint.

Is it possible to destroy fingerprints?• Many criminals have tried… • If an injury penetrates the skin deeply

enough (1-2 mm), a permanent scar may form.

• By intentionally scarring fingerprints, the result would be to leave further identifying evidence. Now the scars make the prints even more unique!!!

• It is impossible to obliterate all ridge characteristics!!!

Principles of Fingerprinting

• Third principle: Fingerprints have general ridge patterns that permit them to be systematically classified.

• 60-65% of the population have loops

• 30-35% have whorls

• 5% have arches

Ridge Characteristics

Loops• Defined: one or more ridges entering

from one side of the print and exiting the same side

• Ulnar loop- the loop enters and exits towards the little finger

• Radial loop- the loop enters and exits towards the thumb

• All loops must have at least 1 delta. A delta is an area of divergence, like the term for a delta in the water sense.

Loop Characteristics

Whorls• All whorls have type lines and at

least 2 deltas.• 4 distinct groups:• 1 and 2) plain and central

pocket loop- at least 1 ridge makes a complete circuit (any form of a circle)

• If an imaginary line drawn between the two deltas touches any one of the spiral ridges, it is a plain whorl. If not, it is a central pocket loop.

Whorls

• 3) Double loop- two loop combine into 1 fingerprint

• 4) Accidental whorl- either contains 2 or more patterns (not including the plain arch) or Is a pattern not covered by other categories

Arches

• The least common of the three groups!

• 2 types:• 1) Plain- Ridges

entering one side and exiting the other side, usually with a rise in the center

• 2) Tented- similar to a plain arch, except instead of gradually rising, it rises sharply in the center

• Arches DO NOT have deltas, type lines or cores!

Plain vs Tented Arch

Types of Prints• 1) Visible prints- prints

that show ridges and patterns after coming in contact with a colored material, like blood, ink, etc.

• No specialty equipment is necessary to detect the print. They are often photographed.

• 2) Plastic Prints- ridge impressions are left in a soft material like putty, butter, wax, etc.

• These prints are photographed, not lifted.

Types of prints

• 3) Latent prints- invisible prints, cannot be seen with the naked eye

• Must be developed by 1 or more methods to be visible.

Locating Latent Prints

• Recent advances in fingerprint technology led to the development of a devise called RUVIS.

• This reflected ultraviolet imaging system can illuminate prints without the use of chemicals and powders.

• It works by reflecting UV light back to the viewer from the print so it is differentiated from its background.

• This works because certain components of perspiration fluoresce.

Detecting Latent Prints

• Chemical methods-• Certain chemicals or

chemical combinations can induce fluorescence that is visible when exposed to a laser.

• Iodine fuming- iodine sublimates from solid to a purple gas. The iodine is heated in the presence of the evidence.

• The iodine fumes “stick” to the constituents of the print making it visible.

Iodine Fuming

• Fuming with iodine is an older method- because the prints fade quickly after fuming is stopped.

• It can be “fixed” by spraying with a starch solution to turn the print blue/purple.

Ninhydrin

• This chemical developer reacts with amino acids present in trace amounts in perspiration to create a blue/purple color.

• Prints develop within an hour to 2 hours.

• Weaker prints may take 24-48 hours to develop.

• The ninhydrin solution is prepared by mixing the powder with acetone or ether to dissolve and spraying on the surface.

Physical Developer

• Physical developers are a chemical mixture using silver nitrate to visualize latent prints.

• This method works when other methods fail…like the ninhydrin or iodine method.

• Chemical treatments like those previously described were the most popular method for detecting latent prints on porous surfaces like paper and cardboard, but now a new method is being used.

Cyanoacrylate Fuming

• Superglue can be heated to produce fumes.

• This is done inside a chamber to produce a white coating on a latent print.

• The process usually takes several hours.

• Now, superglue fuming wands are available to use at the scene.

• Rhodamine dye can be added to create a fluorescence effect.