8th Grade Forensic Science

A Closer Look at Fingerprints

Image from ftp://sequoyah.nist.gov/pub/nist_internal_reports/ir_6534.pdf T. Trimpe 2007 http://sciencespot.net/

Ridgeology: The study of the uniqueness of friction ridge structures and their use for personal identification.1 

The koala is one of the few mammals (other than primates) that has fingerprints. In fact, koala fingerprints are remarkably similar to human fingerprints; even with an electron microscope, it can be quite difficult to distinguish between the two.

Image from http://www.cs.usyd.edu.au/~irena/minutia.gif

As we have learned in our first lesson, a fingerprint is made of a series of ridges and valleys on the surface of the finger. The uniqueness of a fingerprint can be determined by the pattern of ridges and valleys as well as the location, shape, and position of minutiae points, which are points where the ridge structure changes.

The term “ridgeology” was coined by Sergeant David Ashbaugh to describe the scientific evaluation process used for friction ridge identifications.

1Introduction to Basic Ridgeology by David Ashbaugh, May 1999

4. Ridge Characteristics

5. Take a look at the sample fingerprint below to see several ridge characteristics that you might find during a fingerprint examination.

Crossover

Core

Bifurcation (fork)

Ridge ending

Island

Delta

Pore

Scar

http://cnx.org/content/m12574/latest/properties.jpg

http://www.dkfz.de/tbi/projects/bmcv/images/iu_it246_04s_fingerprint1.jpg

6. How many ridge characteristics can you identify in this fingerprint?

Automated Fingerprint Identification System (AFIS)

AFIS is a computerized system capable of reading, classifying, matching, and storing fingerprints for criminal justice agencies. Quality latent fingerprints are entered into the AFIS for a search for possible matches against the state maintained databases for fingerprint records to help establish the identity of unknown deceased persons or suspects in a criminal case.

http://www.fdle.state.fl.us/CrimeLab/images/fingerrint%20comparison%20for%20afis.jpg

When minutiae on two different prints match, these are called points of similarity or points of identification.

Notice the corresponding points on the fingerprints shown at left.

Fingerprint Identification8. For almost a hundred years, the primary method used to examine prints was the point system. An examiner would compare the ridges in two prints, and if enough of the ridge points matched, anywhere from twelve to sixteen, then there was said to be an identification.

Source: http://www.abc.net.au/rn/bigidea/stories/s673661.htm

9. In the past ten years, there has been a shift away from the points system to the system known as “ridgeology”.1 An examiner must determine if there are enough features (not just points) in common to determine if two fingerprints are matches.

Possible features to consider in identification: Overall ridge pattern Individual ridge patterns (ridge ending, bifurcation, dot, etc.) Individual ridge structures (width, shape, position of pores, etc.) Other features present in a print, such as creases, scars, warts, etc.

Examine the fingerprints on your “My Prints” page using a hand lens.

Use the information presented in this lesson to identify unique patterns in the ridges as well as ridge characteristics that might be used to identify the print.

Try It!