Forensic techniques day 1

Indentifying Individual Prints

Fingerprint PrinciplesAccording to criminal investigators, fingerprints follow

3 fundamental principles:– A fingerprint is an individual characteristic; no two people

have been found with the exact same fingerprint pattern. (for the most part…)

– A fingerprint pattern will remain unchanged for the life of an individual; however, the print itself may change due to permanent scars and skin diseases.

– Fingerprints have general characteristic ridge patterns that allow them to be systematically identified.

Fingerprint ClassesThere are 3 specific classes for all fingerprints based upon their visual pattern: arches, loops, and whorls.

Each group is divided into smaller groups as seen in the lists below.

ArchPlain arch

Tented arch

LoopRadial LoopUlnar loop

WhorlPlain whorl

Central pocket whorlDouble loop whorl

Accidentical

Interesting Info

Did you know?Dactyloscopy is the study of fingerprint identification.

Police investigators are experts in collecting “dactylograms”, otherwise known as fingerprints.

Fingerprint Factoid: 60% of people have loops, 35% have whorls,

and 5% have arches

ArchesArches are the simplest type of fingerprints that are formed by ridges that enter on one side of the print and exit on the other. No deltas are present.

Plain ArchRidges enter on one side and

exit on the other side.

Tented Arches Similar to the plain arch,

but has a spike in the center.

Spike or “tent”

LoopsLoops must have one delta and one or more ridges that enter and leave on the same side. These patterns are named for their positions related to the radius and ulna bones, i.e. the bone the loop opening is facing towards.

Delta

L – Radial LoopR - Ulnar Loop

L – Ulnar Loop R - Radial Loop

Radius

Ulna

Left Hand

X-Ray Imagine: http://www.tooloop.com/wp-content/uploads/2013/12/Radius-Ulna-X-Ray.jpg

WhorlsWhorls have at least one ridge that makes (or tends to make) a complete circuit. They also have at least two deltas. If a print has more than two deltas, it is most likely an accidental.

Draw a line between the two deltas in the plain and central pocket whorls. If some of the curved ridges touch the line, it is a plain whorl. If none of the center core touches the line, it is a central pocket whorl.

Plain Whorl

Central Pocket Whorl

Whorls – Part 2Accidental Whorl

Accidental whorls contain two or more patterns (not including the plain arch), or does not clearly fall under any of the other categories.

Double Loop Whorl

Double loop whorls are made up of any two loops combined into one print.

Delta

Delta

Fingerprint Classifications

Also called Ulnar Loop

Also called Radial Loop

Also called central pocket loop

Also called an accidental

Identify each fingerprint pattern.

?A B

CD ERight Hand

Left Hand

Left Hand

Right Hand

Right Hand

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 

1Introduction to Basic Ridgeology by David Ashbaugh, May 1999 Image from http://www.cs.usyd.edu.au/~irena/minutia.gif

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.

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 minutiae points, which are points where the ridge structure changes.

Fingerprint IdentificationWhen minutiae on two different prints match, these are called points of similarity or points of identification. At this point there is no international standard for the number of points of identification required for a match between two fingerprints. However, the United Kingdom requires a minimum sixteen points while Australia requires twelve.

Automated Fingerprint Identification System (AFIS)

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

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.

Ridge Characteristics

• Ridge Ending• Bifurcation• Dot• Island• Lake• Hook

Ridge Characteristics

• Bridge• Double Bifurcation• Trifurcation• Opposed Bifurcation• Ridge Crossing• Opposed Bifurcation/ Ridge Ending

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

Ridge Characteristics

Ridge Crossing

Core

Bifurcation (fork)

Ridge ending

Island

Delta

Pore

Scar

EXAMPLE

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

How many ridge characteristics can you identify in this fingerprint?

Lets Identify a print!

Forensic Science

T. Trimpe 2007 http://sciencespot.net/

Collecting Fingerprint Evidence

• Visible Prints– is an impression left by the friction ridges of a

human finger.• Latent Prints

– the word latent means hidden or invisible, in modern forensics it means any chance or accidental impression left by friction ridge skin on a surface, regardless of whether it is visible or invisible at the time of deposition.

Latent prints are impressions left by friction ridge skin on a surface, such as a tool handle, glass, door, etc.

Prints may be collected by revealing them with a dusting of black powder and then lifted with a piece of clear tape.

Did you know? Camel hair is the most common animal hair used to make fingerprint brushes. Now many brushes (like the one above) are made out of fiberglass.

The cyanoacrylate fuming method (often called the super glue method) is a procedure that is used to develop latent fingerprints on a variety of objects.

Bottom Right: http://www.forensicsrus.com/images/SupergluePrint.jpg

Magnetic powder can also be used to reveal latent prints. This type of powder works better on shiny surfaces or plastic baggies or containers.

Top Left: http://www.stapletonandassociates.com/images/MagPowder.jpg

Bottom Left: http://www.ok.gov/osbi/images/ninhydrin%20print.jpg

Click the icon to view the Crime 360Super Glue Video

Some investigators use fluorescent powder and UV lights to help them find latent prints on multi-colored or dark surfaces.

Ninhydrin is a chemical that bonds with the amino acids in fingerprints and will produce a blue or purple color. It is used to lift prints from surfaces such as paper and cardboard.

Directions:1 - Cover your table with white butcher paper or newspaper. You must dust everything on the paper!

2 - Get a lifting kit from your teacher that contains black powder, brushes, and clear tape.

3 - Press the pad of your right thumb on a CD or glass slide to make a print. Place on the paper covering your table.

4 – Dip a brush lightly into the container of black powder and then tap off the extra on the lid. You only need a very small amount of powder to dust the print.

5 – Hold the brush over the print and rotate it between your thumb and fingers. Use the brush to remove any extra powder.

6 - Use a small piece of clear tape to lift the print and place it in the box on your worksheet.

CAUTION: The black powder will be messy and isn’t easy to clean up. Don’t dust anything without permission!

Clean Up

1 – Clean off the CDs or glass slides and put them back in the kit with the brushes and tape.

2 – Have someone help you fold the paper in half and tap it to return the extra black powder to the container.

3 – Put the black powder in the box and have it checked in by your teacher.

4 – Get a towel and “dry” wash the table – especially the edges that weren’t covered with paper.

5 – Get a wet towel to wash off the table and then wipe it with some dry towels. Keep cleaning until all the black powder is off the table!

It’s time to makesome prints!

Avoid Partial Prints

GOOD PRINTGet as much of the top part of your finger as possible!

Directions1st – Roll the “pad” portion of your thumb over the ink pad from the left side of your thumb to the right. You do not have to push down really hard!

2nd – Roll the “pad” portion of your thumb from the left side of your thumb to the right in the correct box on your paper to make a thumbprint.

3rd – Continue this process to make a fingerprint of all ten fingers on the “My Prints” worksheet.

4th –Use your notes and a magnifying lens to help you figure out what type of pattern is found in each of your fingerprints. Label each one with the pattern’s name.