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Latent Evidence: Impression Evidence Information

 

FINGERPRINT IMPRESSIONS

 
 

On the palmar and plantar portions of the hands and feet, each person has a unique and permanent (barring scarring or injury) arrangement of ridges and furrows, called friction ridge skin.  You can think of this skin like the rubber portion of a stamp.   

 

The term "latent" means "hidden".  Latent prints are most commonly fingerprints or palm prints that are collected from a crime scene.  Latent prints usually need to be processed or developed with a chemical or physical developer in order to be visible to the naked eye.  

 

Latent prints can be left by simply touching an object in a crime scene.  The ridges of the hands and feet are composed of sweat pores, but other portions of the body, such as the face, are composed of a variety of glands and pores, including oil glands.  Because of this, the ridges of the hands accumulate sweat as well as oil, and these can be easily transferred quite routinely.  Anything that accumulates on the ridges of the finger can be transferred and left behind in the same formation as the fingerprint ridges. 

 

To use the stamp analogy once more, think of your finger as the stamp and any accumulated substances (sweat, oils, and various other substances) that it acquires as the "ink".  When a stamp is placed on a surface, the ink is left behind in whatever pattern the stamp holds.  Similarly, when a person places his/her hand on a surface, any accumulated substances will be left behind in the pattern of the ridges.

 

In order to view latent prints, many times a processing technique must be used.  Listed here are a variety of processing techniques that can be used including (but not limited to):  

                  × Cyanoacrylate/Superglue (CA) Fuming

                  × Black Powder

                  × Dye Staining

                  × Indanedione

                  × Small Particle Reagent (SPR)

                  × Leucocrystal Violet (LCV)

                  × Amido Black

                  × Ninhydrin

 

Some examples of latent prints that have been processed with a few of these techniques are picture below.

 

 

Lab_leu_fingerprint processing_sf1

 

    

Lab_leu_fingerprint_sf5

Figure 1:  Example of ridges and furrows.*

 

 

Lab_leu_fingerprint_sf3

Figure 2:  Anatomy of the friction ridge areas of skin.*

A) Accumulated fat.  B) Sweat gland.  C) Sweat duct.  

D) Mucous Layer.  E) Epidermis - outer skin.  

F) - G) Pores.  H) - I) Friction ridges.  

J) Furrow.  K) Dermis "inner" skin.

 

 

 

 

 

 

 

 

 

 

Figure 3:  Examples of processed latent prints.  

           (top left) LCV; (bottom left) SPR; (middle) Indanedione;

                  (top right) Acid Yellow; (bottom right) CA fumed

Lab_leu_fingerprint_bar_sf4

   

 

Figure 4: Known Footwear vs. 

Unknown Footwear Impressions

(top left) unknown shoe impression casting from crime scene; 

(top right) known shoe submitted for comparison to casting; 

(bottom left) known shoe submitted for comparison to unknown shoe impression to the right; 

(bottom right) unknown shoe impression collected from crime scene

  Lab_leu_footwear examples_sf1

————————

  Lab_leu_tire impressions_sf1

Figure 5: Tire Tread Impressions

(bottom right) unknown tire impression photographed at the crime scene before casting; 

(bottom left and top right) castings taken from unknown tire impressions at the crime scene; 

(top left) inked known tire impression

 

 
FOOTWEAR AND TIRE TREAD IMPRESSIONS

Footwear and tire tread impressions can be latent or visible impressions that are left in 2-dimensions (2-D) or 3-dimensions (3-D).    

 

2-D impressions will be any impression that only has length and width measurements.  

 

    2-D footwear impressions are typically found indoors and are associated with objects  touched at the crime scene.  This can include any object or surface in the crime scene.**  

    An example of this could be a perpetrator who steps on some loose papers that are on the floor of the crime scene and leave a dirt impression on the paper.

 

3-D impressions will have length, width, and depth measurements.  

 

    3-D footwear impressions are typically located outdoors in substrates such as sand, clay, mud, or snow, but can be found in any similar substrate that is malleable.**  

    An example of this could be a perpetrator stepping in the mud right outside of a crime scene, and a footwear impression of his shoe/boot.

 

Processing 2-D and 3-D footwear impressions:

 

    2-D impressions are normally photographed at a 90 degree angle with a scale.  For certain 2-D impressions an electrostatic dust collector can be utilized.

 

    3-D impressions are photographed in the same way, but a casting material can also be used to "lift" the impression and retain impression details.

    

 

 

*Images courtesy of American Institute of Applied Sciences. (2009). Friction Ridges. 6-7. Youngsville, NC: American Institute of Applied Sciences.

**Cassidy, M. J. (1995). Footwear Identification. Salem: Lightning Powder Company.