Lecture 3 - Fingerprint Analysis

Question 1

Key Features of Fingerprints (3)

Answer 1

1. Fingerprints remain unchanged throughout your life.
2. Fingerprints form sometime during embryonic development.
3. No two fingerprints are the same. Even for identical twins.

Question 2

Can you change/remove fingerprints?

Answer 2

No, it is incredibly hard to do so. No disease does so. No injury (short of amputation). So if the tissue and epidermis can come back then the ridge pattern can come back.

Question 3

No two fingerprints are the same.

Answer 3

Even identical twins have different fingerprints. So, fingerprints are influenced by genetic input AND developmental input. (possibly environmental input).

Question 4

In order to differentiate fingerprints…

Answer 4

we systemically classify.

Question 5

~2000 BC, Ancient Babylon

Answer 5

Used fingerprint impressions for
business transactions

Question 6

200 BC-200 AD, China

Answer 6

various dynasties use fingerprints for
documentation. Link between handprints and burglaries

Question 7

Late 17th Century

Answer 7

Got a description of ridge patterns as it relates to skin anatomy

Question 8

1880s

Answer 8

physicians proposed that skin ridge patterns were unique and could be used to ID criminals
(Anthropometry - study of human proportions)

Question 9

Francis Galton (1822-1911)

Answer 9

developed the first systematic study of
fingerprint patterns, developed classification system still used today

Question 10

Biology of Fingerprints

Answer 10

Fingerprints = Friction Ridge Skin - it is described as a topographical pattern of hills/ridges and valleys/furrows on palms of hands and feet

Created by epidermal protrusions beneath the outer layer of skin:
‘intermediate ridges’

Spatial pattern of epidermal ridges and, therefore, the overall
fingerprint can vary in general features/shapes as well as finer
scale variations

Question 11

Five general ridge patterns

Answer 11

Right Loop, Left Loop, Whorl, Arch, Tented Arch (Combinations of these are present in a fingerprint)

Question 12

Further Classification

Answer 12

variations within these five general characteristics

classification system based on Spatial patterns, geometry, the features within these class patterns

Question 13

Uniqueness of Print

Answer 13

Comes from all of these different patterns, the abundance of these features, the minutiae, and their spatial location

Question 14

Manual Matching

Answer 14

Count the identical features between the prints. The higher the number, the stronger the association, and the higher confidence in identification.

There are general characteristics and then the minutiae are separated into primary, secondary, and sub-secondary.

This is very laborious, specific training.

Question 15

AFIS

Answer 15

Automated Fingerprint Identification System - Two goals: One was to store fingerprints collected by the FBI and the other was to conduct automated searches.

Separate AFIS databases maintained for various individual
jurisdictions (e.g., state, county, regional)

Been useful for solving cold cases.

Question 16

Why might it be beneficial to combine all DNA databases into one? Why not?

Answer 16

If someone commits a crime where they don’t live, then they can be traced back to wherever they are from.

Not - want to uphold their authority. There would need to be a set way for everyone to collect fingerprints, iodine fuming, etc that is compatible with the database.

Question 17

How are fingerprints left as evidence at the crime scene? What are
they chemically, biologically, physically…? (19)

Answer 17

The Ridges of fingers have sweat glands/pores (eccrine glands). When you touch something, these pores leave behind Sodium, Potassium, Calcium, Iron, Magnesium, Zinc, Chloride, Sulfate,
Ammonium, Proteins, amino acids, lipids, glucose, urea, glycogen, uric acid, pyruvate,
Dirt, other exogenous
substances

Question 18

Three types of fingerprints deposited at the crime scene.

Answer 18

Patent fingerprint: visible to the naked eye, usually left in dark
and/or viscous medium (blood, grease, etc…)

Plastic fingerprint: print also visible to the naked eye but left in soft
medium… distinct 3D structure

Latent fingerprints: Not visible to the naked eye, needs to be
visualized with another substance or chemical procedure

Question 19

One fingerprint doesn’t have enough sweat accumulated to show up under UV light.

Question 20

Visualization Methods for Latent Prints

Answer 20

All of these bind or interact with one of the biological components that are secreted in your sweat ducts along the ridges of your fingerprint.

Question 21

Powder-based development: oldest forms of fingerprint visualization
(~100 years!)

Answer 21

Compositions vary: typically combination of inorganic ions, e.g.,
FeO, Pb, Cd, Cu, Si

Powder based visualization can be performed at the crime scene
*
Pictures can be taken …OR… entire fingerprint can be transferred
via ‘tape-lifting’
Key Features of Fingerprints

Question 22

Amino Acid

Answer 22

R-group, amine group, (NH2), Carboxyl (-) this is what binds to positively charged ions in the powder

Question 22

Lipids

Answer 22

negatively charged head is going to be interacting with the positive charge in the powder.

Question 22

Iodine Fuming

Answer 22

A gaseous iodine, interacts with the hydrophobic tail of the phospholipid. As it fumes, it forms complexes with the tail of the phospholipid, showing up as a reddish brown color. Wherever iodine shows up, lipids (from sweat) are present. Shows print.

Question 23

Ninhydrin visualization

Answer 23

Ninhydrin binds to proteins and amino acids. Ninhydrin reacts with amino acid to form a complex. Due to aromatic groups, it dimerizes, allowing for a colorless to dark purple color change. Anywhere with amino acids will react. You can spray ninhydrin and it also occurs at room temperature.

Question 24

cyanoacrylate ester (super glue)

Answer 24

It binds to fatty acids and lipids. It then dimerizes and creates a white precipitate (superglue). Oils and compounds are deposited along the pattern as they bind to lipids, revealing the print and allowing for analysis. (done in a fume hood).

Question 25

How do you decide whether fingerprint development, identification is
performed at the crime scene or back in the laboratory?

Answer 25

Crime-Scene dependent
ex: car, probably dusting
Black powder is usually the least sensitive technique.

Who? crime scene investigator, lead law enforcement, detective investigator. So the same people that are making decisions about what evidence to collect, they’re gonna be making initial assessments of what.
Also depends on severity/class of crime.

depends on WHAT they’re investigating.

Question 26

Madrid Train Bombing

Answer 26

2004 -
10 explosions across four commuter trains during rush hour
~190 killed, >1900 injured

Fingerprint recovered from the plastic bag near one of the explosion sites

Initial analysis and database search showed no matches

For AFIS/other fingerprint matching databases to work well, the conditions should be ideal. The print should be clear and complete. That was not the case. However, due to pressure and worries about terrorism, the print kept getting tested. Also, explosion obscured print.

Came up with ten markers - compared to database and got 5 matches. Took Brandon Mayfield into custody. Lawyer in Oregon.

FBI reached a $2M settlement with Mayfield, found they
‘misapplied’ the methodology for analysis and comparison

Technically went wrong and bias was present (Mayfield was Muslim, married to Egyptian, represented accused terrorists)

Question 27

Figuring out the error rate for fingerprint analysis didn’t happen until 2009.

Question 28

Nothing wrong with the science (prints/DNA). Problems arise when DNA/prints are damaged yet analysts still make conclusions based on them.