Forensics - Unit 3 (Fingerprints)

What are the 3 categories of fingerprints?

1. latent

2. patent

3. plastic

What is a latent print?

• an invisible print

• most common

What is a patent print?

• a visible print that occurs after someone has come into contact with a colored source 

  • ex: ink, blood, paint, grease

What is a plastic print?

• a visible print that is usually impressed into a soft surface

  • ex: wet cement, wax, putty, mud, wet sand, food 

What are the 3 classes of fingerprints?

1. loops 

2. whorls

3. arches 

What are the characteristics of a loop fingerprint?

• ridge: the ridge enters on one side and exits the same side 

• delta: 1 

• types: ulna (pointed to pinky) and radial (pointed to thumb) 

• most common 

What are the characteristics of a whorl fingerprint?

• ridge: the ridge enters on one side and exits in the middle of the print

• delta: 2

• types: plain whorl, central pocket loop whorl, accidental loop, and double loop

• 2nd most common

What are the characteristics of an arch fingerprint?

• ridge: the ridge enters on one side and exits on the other

• delta: 0

• types: plain arch and tented arch

• rare

When is carbon powder used to develop prints?

• used on non-porous, non-textured surfaces

When is magnetic powder used to develop prints?

• non-porous, shiny, textured surfaces 

  • ex: furniture, faux leather, plastic bags and bottles

When is iodine used to develop prints?

• non-metallic, both porous and non-porous surfaces

• normally used for prints that have been outside 

• reaction is orange

When is ninhydrin used to develop prints?

• used on thin, porous surfaces

  • ex: money, paper, thin cardboard, cigarette

• reaction is purple

When is silver nitrate used to develop prints?

• used on thick porous surfaces

  • ex: wood 

• reaction is gray/silver

When is fuming used to develop prints?

• also called cyanoacrylate/ super glue method 

• non-porous, dark , small objects

  • reaction is white

What is a minutiae? 

• characteristics on a fingerprint (delta, ridge characteristics)

What is the difference between porous and non-porous?

• porous — absorbs liquid 

• non-porous — doesn’t absorb liquid 

What did Locard do?

• created the Principle of Exchange 

  • is the reason why fingerprints are left behind 

Who was William Herschel?

• has the first official use of fingerprints 

What did Francis Galton do?

• created the book fingerprints

  • discussed the anatomy of fingerprints, HOWEVER it was too difficult to understand so it was never implemented

What did Sir E.R Henry do?

• simplified Galton’s work so that it could be implemented by Scotland Yard

What is AFIS?

• Automatic Fingerprint Identification System 

  • scans a fingerprint to identify and breaks it down into its minutiae points

  • will then spit out 15-20 fingerprints that are close to the given fingerprint

    • the final decision is from a fingerprint expert

When is a fingerprint considered class evidence?

• when a fingerprint is identified to be either an arch, loop, or whorl

When is a fingerprint considered individual evidence?

• when you have many points of similarity between two fingerprints

What are point of similarity and how many are needed to make a positive match?

• happens whenever there are matching minutiae points 

  • GBI: 10-12 matching minutiae 

  • FBI: 7-10 matching minutiae

What are the 3 Principles of Fingerprints?

1. Fingerprints are individual

2. A fingerprint will remain unchanged during an individual’s life 

3. Fingerprints have general ridge patterns

While escaping a crime scene, a burgular steps in the soft dirt around the victim’s driveway leaving a shoe impression. What type of print is this?,

• a plastic print 

How would we attempt to develop and lift a fingerprint from a plastic bottle of hand sanitizer?

• magnetic powder 

What is the difference between a plain whorl and a central pocket loop?

• Plain whorl

  • if you drew a line connecting the two deltas, that line cuts through the whorl pattern 

• Central pocket loop 

  • if you drew a line connecting the two deltas, that line falls below the whorl pattern 

If the suspect was leaning against a leather couch, what method would be used to develop that print?

• carbon powder 

What does it mean to “develop” a fingerprint?

• to turn a latent (invisible) print to a patent (visible) print

What are fingerprints made out of?

• ridges that hold sweat and oil