Lab Exercise 4 PDF

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Lab exercise 4...

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Exercise 4 : Shoeprint identification and individualisation Introduction Shoeprints can be very roughly divided into two categories : impressions and surface transfer marks. Impressions are prints made in sand, soil, snow or any other soft medium. They should be protected, photographed and then cast for permanent record. Surface transfer marks are made when the sole of footwear has been contaminated with anything from dampness to dust. Surface transfer marks may be recovered by electrostatic lifting or by tape lifting. Latent shoeprints may also be enhanced by the use of fingerprint powders, just like latent fingerprints.

Shoeprint evidence can           

Help identify or eliminate a suspect Determine the brand of a shoe by comparison with a database Determine the size of shoe Positively identify a shoe by its unique characteristics Prove an individual’s presence at a crime scene Aid in reconstructing a crime scene Show the number of perpetrators involved Help prove involvement in a crime Reveal the time frame when the impression was made Reveal the sequence of events Prove or disprove an alibi

A questioned footwear examination establishes Class Characteristics (CC) (pattern size, length etc), determines Wear Areas and Patterns (WP) and reveals Individualising or Accidental Characteristics or Patterns (AP). Class Characteristics are intentional or unavoidable characteristics that repeat during manufacture and appear on all shoes of a particular type. Wear Patterns are the result of random removal of material from the outer sole and heel as shoes are worn. Wear patterns serve as supplemental identifying features. Most people wear all their shoes out in the same way – as a result, wear patterns can help associate questioned footwear prints to know pieces of footwear.

Accidental Characteristics are cuts, tears, gouges, foreign body adherence or inclusion (gum pebbles, grass etc) and random wear marks. These characteristics can often individualise a known shoe to a questioned print. These classifications apply to both impressions and surface transfer prints. Your task for this exercise is to compare known shoes to a questioned footprint and determine which (if any!) of the shoes made the print. There is also some evidence to suggest that the size of the print is related to the height of the owner. http://www.usc.edu/CSSF/History/2002/Projects/J1003.pdf (on 8th August 2005)

By using the equation Height in cm

=

(length of print in cm x 4.3) + 60.4

it is possible to approximately determine the height of the maker of a footprint. There is a similar relationship between height and shoe size, but adjustment needs to be made for gender! Method

Collect your tray containing sand and an impressed footprint. Measure and sketch or photograph your print before you start to cast it. Why is this important? Build a “dam” round the footprint using the strips and tape provided. Collect a bag containing 300 g of dental plaster and mix in180 – 200 mL of water. Add the water all at once or the plaster will set too quickly. Slosh the mix around until it is the consistency of thin cream, then carefully pour it into the mould, being careful not to disturb the footprint. You need to be quick at this stage – the plaster starts to set really quickly! The plaster will be solid in around 30 mins – after 10 mins or so, scratch your initials into the back of the cast for future reference. Place the cast in the oven to dry for around 60 minutes. While you are waiting for the cast to dry, collect a surface transfer mark to identify. This surface transfer mark is a Questioned Footwear Print which has been found at a crime scene.

Try to identify the footwear from the surface transfer mark. Use the CC, WP and AP method of identifying features as described on the previous page. You can write directly on to your copy of the transfer print and include it in your report. Available in the laboratory are known footwear samples from various suspects and others who may have been present at the crime scene – you should look at these only when you have FINISHED your evaluation of the surface print. (Why do you think this is so? Answer that in your report.) To help you with your conclusions, consider the following points : For a positive identification, ALL class characteristics of the questioned impression must be present on the known shoe, and one or more identifying or accidental characteristics must also appear on both. For a positive elimination, the class characteristics should not match. Not suitable for comparison means not enough of the print is available or clear enough for examination. Consistent in class characteristics means it’s the same type of shoe. Consistent in class characteristics and wear pattern means it’s the same type of shoe and probably worn by the same person.

When your plaster cast is dry enough, dust off the sand and repeat the identification exercise. This time you can draw a sketch of the print to help identify the characteristics on which you base your identification. Or use your camera to take a picture. It is often easier to determine detail on the cast if you highlight it with chalk dust. Remember, you must fully evaluate the cast print BEFORE comparing it with the known shoewear. On your picture or sketch, point out the areas you are going to discuss in your report, using the CC, WP, AP protocol as before. Calculate the height of the owner of the recovered print/s using the equation given earlier. Also measure your own footwear and calculate your height. Is this a good method of determining height? Use the answer in your discussion of results in your report. At some stage during the lab you will see the ElectroStatic Lifting Apparatus (ESLA) in action - you do not need to write about this in your report.

(Experiment based on one in “Forensic Science Laboratory Experimental Manual and Workbook”, T. Kubic & N. Petraco, 2003, CRC Press)

Lab 4. Shoeprint identification : marking guidelines

“topic” marked Layout Casting impression Analysis/comparison for

Possible mark 2 1

transfer print Analysis/comparison for

1½

impressed print Height calculations for

1½

both prints Discussion & conclusion Total =

1 3 10

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