FORS 201 - LECTURE 8

What can footprint impressions tell us about a scene

• minimum number of people at a scene

• reconstruct movement through a scene

• match known foot wear

what can type impressions tell us about a scene

• poition and orientation of a vehicle

• direction of travel

• identify vehicle

what does impressions examination incude at the scene

• detection

• documentations

• collection

• preservation of questions impressions

what does impressions examination include in the lab

• analysis of questioned impressions and a comparison with known footwear/tyres using test impressions

what is a test impression

• impression made that can be used as an aid for comparison purposes

what is a questioned impression

impression made by an unknown source

what is a known impression

an impression from a known source that can be used as a comparison to determine the source of unknown impression

how are impressions detected

• found using oblique lighting

• photographed and sketched in situ

what are some methods of collecting impressions

• lifting

• casting

what is lifting

• if a print is on top of a surface, and the surface cant be collected, the print is lifted off the surface using various methods depending on the surface

what is casting

• if a print is impressed into a surface then a cast is made to get the impression

what is the basic lab process when analyzing impressions?

• analysing the questioned impression

• narrow down some known impressions

• compare questioned and known impressions

what are class characterisitics

• general characteristics that group items (outsole design, size, shape, logo, text etcz0

what does class characteritics allow us to do

• narrowing down of the possible type of shoes that could have made an imprint but dont individualise

• type of show can be determined by searching databases created by manufacturers

what is wear characteristics

• pattern of erosion of the outsole

• looking at amount, location and pattern

what are the types of wear characteristics

• general wear eg heel scuffing

• specific wear eg wear that is unusual: some people are everters/inverters, injury and disability can also contribute

what are randomly acquired characteristics

• unique, usually accidentally acquired characterisitcs that accumular over time

• features on footwear outsoles that are not shared by an other shoe

what are some examples of RACs

• mould features

• shallamach patterns

• cuts, nicks, scratches

• stone holds

• embedded items

what are shallamach patterns

• severe wear pattens

• extreme pressure that cause teh rubber to buckle and create these patterns

what is swgtread

• scientific working group for shoeprint and tire tread evidence

• it is a range of conclusions that you display your evidence in

what are the possible conclusions

lacks sufficient detail

exclusion

indications of non association

limited associated of class characteritics

associations of class characteristics

high degree of association

identification

explain what ‘indications of non association’ is decribing

• questioned impression exhibits dissimilarities when compared to the known footwear or tire; however, the details or features were not sufficiently clear to permit an exclusion

explain what limited association of class characteritics is describing

some similar class characteristics were present; however, there were significant limiting factors in the questioned impression that didn't allow you to strongly associate it to the known footwear

explain what association of class characteristics is describing

class characteristics of both design and physical size must correspond between the questioned impression and the known footwear or tire. Correspondence of general wear may also be present. 

explain what high degree of association is describing

questioned impression and known footwear or tire must correspond in the class characteristics of design, physical size, and general wear. For this degree of association there must also exist: (1) wear that, by virtue of its specific location, degree and orientation make it unusual and/or (2) one or more randomly acquired characteristics

explain what identification is describing

highest degree of association expressed by a footwear and tire impression examiner. The questioned impression and the known footwear or tire share agreement of class and randomly acquired characteristics of sufficient quality and quantity

what is forensic serology

• the detection, characteristic, identification and typing of body itssues and fluids in native form or as residues left at a crime scene

what are the two types of testing

• presumptive tests

• confirmatatory tests

what is a presumptive test

• screening tests that indicates the possibility of a material of interest

what is a confirmatory test

• a test that is specific for the presence of a specific residue of interest and reduces or eliminates false positive results

what do presumptive tests tell us when it comes to blood

• helps locate and determine if a stain is blood

what does a confirmatory test tell us when it comes to blood

• helps determine if it is human

what does a positive presumptive test tell us

• it doesnt identify a specific material

what does a negative presumptive test tell us

• not confirmation of a materials absence

• it could mean incorrect sampling, not enough substance etc

describe the mechanism that presumptive tests are based on

• the principle that haemoglobin is an oxidant

• produce a colour or light change when reacting

what is a imitation of the mechanism of presumptive tests

• since it functions on the principle that heamoglobin is an oxidant

• we can get false positives with other oxidants such as bleach, horseradish, iron, copper, raw potato potato.

what are some examples of colour presumptive tests

tetramethylbenzidine - blue/green colour

kastle-meyer - pink colour

what are some exmaples of light tests for blood

• luminol (blue light in the dark)

• fluorescein (blue light using a specific light source)

what should be done following a positive presumptive test

• a confirmatory test for human blood should be undertaken

what kind of test is the only one that can identify a specific biological material

• confirmatory tests

describe the mechanism behind confirmatory tests

• use antibodies to confirm the presence of blood

what is some examples of confirmatory tests

• ABAcard hematrace

• RSID

how does ABAcard hematrace work

• uses an antibody that will react with human haemoglobin

how does RSID blood test work

• antibodies that react with glycophorin (protein in RBCs)

what are some limitations with the ABAcard hematrace test

• non human apes and ferrets give false positives