Fingerprints are formed between the third and fourth month of fetal development when sweat glands in the skin link together to form unique ridge patterns. The basal layer of skin grows at a different rate than the layers above and below it, causing it to fold into intricate ridge shapes. Materials secreted from sweat pores, like oils and water, are left behind on surfaces when fingerprints are transferred. There are three types of fingerprints found at crime scenes: latent prints that require processing to see, patent prints that are visible, and plastic prints that make three-dimensional impressions. Fingerprints are analyzed by their ridge characteristics like endings, forks, islands, dots and used by AFIS to identify matches on file.

1. Fingerprints and Ridge
Characteristics

2. 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.

3. Formation of Prints
o 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.

4. Structure of Skin

5. Structure of skin 3D!!

6. 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.

7. • 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.

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

9. 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

10. 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

11. 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

12. 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

13. 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).

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

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

16. Ridge ending

17. Fork/Bifurcation

18. Island ridge

19. Dot

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

21. Spur

22. Double bifurcation

23. Eye

24. Trifurcation