Forensics- Impression Evidence

Core Patterns

Plain arch

Tented arch

Plain whorl

Central pocket loop whorl

Double loop whorl

Accidental whorl

Loop

Minuitae

Plain arch

Tented arch

Plain whorl

Central pocket loop whorl

Double loop whorl

Accidental whorl

Loop

3 impression categories

• Patent impressions are two-dimensional

  • Ex. bloody shoe prints, wet paint tire mark

• Plastic impressions are three-dimensional

  • Ex.  bite to the skin, snow shoe print

• Latent impressions are hidden to the eye  

  • Ex. clear oils of the skin leave a fingerprint only revealed through dusting

Shoe Impressions

• usually class evidence

• shoe print size indicates foot size - estimated height

• the depth of shoe print- estimated persons weight / if they were carrying something

• type of shoe - infer someones job / personality

suggested equations

Female height in cm = (4.5 X shoe size) + 140 cm 

Male height in cm = (5.3 X shoe size) + 140 cm

shoe print analysis

photograph, measure and record, make a cast (plaster if possible)

Latent shoe prints

• Luminol spray

  • makes cleaned up bloody footprints visible

• Electrostatic Dusting (similar to fingerprinting)

  • makes a small amounts of dust left behind by a shoe visible

Individualizing shoe prints

• body weight

• direction of toes

• how they walk

• pronation and supination

• surface they walk on

• holes, cuts, or marks in the sole of the shoe

How marks form

interaction of two objects - harder object leaves mark of softer object

tool mark

Any indentation, abrasion, or cut made when contact occurs between a tool and an object

• The impressions can link the tool to a crime scene and potentially to the owner

• 3 Plastic Impression Tool Mark Types

  • Indentation mark

  • Abrasion mark

  • Cutting marks

Indentation tool marks

result when a tool is pressed against a softer surface

• Ex. a screwdriver used to open a window will be pressed into the softer window frame

Abrasion tool marks

result when a tool is slid back and forth (scratches)

• Ex. a saw or a file

Cutting tool marks

result from a pinching action (cut marks are produced along the edge as a surface is cut)

• Ex. tools like wire cutters,     scissors

Tool mark examination

1. Photograph, measure and record

2. Make a cast- preserve tool mark impressions

• silicone or rubber-based casting materials

• dust for fingerprints before applying casting material