Fingerprints Minutiae Patterns

What Are Fingerprints? Raised ridges of skin on the hairless surfaces of hands and feet (Dermal Ridges) Primates and other animals have them Provide traction and every ridge contains a gland

When Do Fingerprints Form? Begin to develop in the 10th week of gestation and are complete by the 24th week Chance, environment, and heredity all play a role in the development of an individuals fingerprints

Three Principals of Fingerprints A fingerprint is an individual characteristic No two fingers have the same fingerprint Identical twins are similar but not identical Fingerprints remain unchanged during a lifetime Fingerprints have general ridge patterns that permit them to be classified

Three Types of Fingerprints Plastic Impressions. Made in soft material like butter, soap, etc. Visible Prints. Prints made when fingers have been covered in blood, dirt, oil, paint, etc. Latent Prints. Prints not visible to the human eye, hidden, unseen until treated.

Methods for Making Latent Prints Visible. Chemical Methods Iodine fuming Ninhydrin Silver Nitrate Super Glue Fuming Powder Methods Black Powder for light surfaces White powder for dark surfaces

Dusting for Fingerprints

Minutiae Minutiae patterns (Ridge Characteristics)- Ridge endings, bifurcations, enclosures and other ridge details, which must match in two fingerprints in order for their common origin to be established.

Bifurcation- when the pattern splits from one line into two Enclosures- an enclosed loop pattern Short Ridge- short line pattern Island- a small dot with no lines touching it

Ridge Crossing- When two lines cross, forming an X formation Ridge Ending- A long line that stops in the pattern

Examples of Minutiae

Identification of Minutiae You must find 12 points of minutiae to match a print from a scene of a crime to a person’s print Label each with a number and a line to show its location Make a key at the bottom of the two prints

Identification of Minutiae Bifurcation 4. Ridge Ending 7. Bifurcation Bifurcation 5. Enclosure 8. Bifurcation Bifurcation 6. Bifurcation 9. Ridge Ending

Classification of Fingerprints Loop- A class of fingerprints characterized by ridge lines that enter from one side of the pattern and curve around to exit from the same side of the pattern. About 60-65% of the population have Loop patterns.

Whorl- A class of fingerprints that includes ridge patterns that are generally rounded or circular in shape and have two deltas. About 30-35% of the population have whorl patterns.

Four Types of Whorls Plain Whorl Double Loop Central Pocket Whorl Accidental

Arch- A class of fingerprints characterized by ridge lines that enter the print from one side and flow out the other side. About 5% of the population have Arch patterns

Primary Classification The primary classification of fingerprints, takes the ridge patterns of all ten fingers of a person and turns them into a fraction. The first step is to pair up fingers, placing one in the numerator and one in the denominator.

The presence or absence of the whorl pattern is the basis for the determination of the primary classification. If a whorl pattern is found on any finger of the first pair it is assigned a value of 16, on the second pair a value of 8, third pair 4 fourth pair 2, last pair 1. Any finger with an arch or loop is assigned a 0.

R Index + R Ring + L Thumb + L Middle + L Little + 1 R Thumb + R Middle + R Little + L Index + L Ring +1

In other words: Pair Whorl pattern number 1: RI/RT 16 2: RR/RM 8 3: LT/RL 4 4: LM/LI 2 5: LL/LR 1

Determine your Primary classification Ms. Persico’s Primary Classification: 0 + 8 + 0 + 2 + 0 + 1= 11 0 + 0 + 4 + 0 + 1 + 1 6

About 25% of the population falls into the 1/1 category: that is, all their fingers have either loops or arches, and no whorls. Ridge patterns help impart class characteristics to the print, it is the type and position of ridge characteristics that give it it’s individual character.

Automated Fingerprint Identification Systems Before 1970, the process of storing and searching for fingerprints was a cumbersome process. In about 1970, computer technology allowed law enforcement agencies to store and recover fingerprints from a database. These systems are called AFIS- Automated Fingerprint Identification Systems.

The basis of AFIS is the ability of a computer to scan and digitally encode fingerprints so that they can be subject to high-speed computer processing.

The AFIS uses automatic scanning devices that convert the image of a fingerprint into digital minutiae that contain data showing ridges at their points of termination (ridge endings ) and the branching of ridges into tow ridges (bifurcation).

The AFIS is able to search for a set of 10 fingerprints against a file of 500,000 10-finger prints in about 8/10 of a second. The AFIS will show a correlation between the known and unknown print, but the final decision is made by a professional examiner.

EXAMPLE of the AFIS in action: In Los Angeles, minutes after the AFIS received it’s first assignment, it found a match to an individual who had committed 15 murders and was terrorizing the city. It would have taken a single technician, searching the 1.7 million prints, 67 years to come up with the perpetrator.