Fingerprints and Ridge Characteristics

Fingerprint origin

• Between the 3rd and 4th month of fetal development the sweat glands form in the skin through small pores. Pores link together to form a series of ridges that are unique to every individual.

Formation of Printso Skin consists of: • Inner layer—dermis • Outer layer—epidermis• Basal layer in between

o Basal layer grows faster than the layers above and below it

o Basal layer collapses and folds to form intricate shapes

o The folds and pores create unique patterns even amongst identical twins.

Structure of Skin

Structure of skin 3D!!

How are fingerprints left behind?

• Materials are continually secreted from the pores in the skin within the ridges of the fingers.

• 98-99% of the secreted material is water and the other 1-2% is other organic and inorganic materials.

• Any sebaceous oils on the fingers is transferred from other areas of the body and is collected in the ridges.

• Other objects that have an oily or greasy residue also transfer materials to the fingers when touched.

• All of the materials that gather in the ridges can be transferred from the finger to the touched object…leaving behind a distinct fingerprint

Types of prints found at Crime Scenes

• There are three types of prints that can be found at the scene of a crime.– Latent– Patent– Plastic

Latent prints

• Latent prints are considered to be any print that is not easily seen.

• They require Processing with the use of powder and/or chemicals like super glue fuming

Patent prints

• Patent prints are any print that can be easily seen because they were made with a substance on the fingers…such as blood, oil, or ink.

• Patent prints need to be photographed and then collected using lifting tape…they do not require chemicals

Plastic prints

• Plastic prints are three-dimensional impressions made in a substance that holds the shape of the ridges on the fingers such as putty, clay, or wax

• Plastic prints should be photographed first and foremost and then attempts can be made to get an impression using plaster or other casting materials

Analyzing prints

• In the past fingerprints were analyzed by fingerprint analyzers and then they would be compared to fingerprints on file.

• Now, computers do the work by digitally scanning prints into a large database called the Automated Fingerprint Identification System (AFIS).

• The computer uses an automated scanning device to convert the image of a fingerprint into digital ridge characteristics

What is analyzed?• Ending ridge• Fork (bifurcation)• Island ridge• Dot• Bridge• Spur• Eye• Double bifurcation• Trifurcation

Ridge ending

Fork/Bifurcation

Island ridge

Dot

Delta & Bridge

The core should also be noted because it is an important characteristic in determining prints.

Spur

Double bifurcation

Eye

Trifurcation