1. Collecting Impressions as Evidence

2. Impressions can be made by:
Shoes and footprints
Tires and tire tracks
Tools
Teeth

3. Collecting impressions
Priority on preserving the impression and/or its reproduction.
Photograph first, with scale, to show all observable detail
Shoot various angles
Use side-lighting
Show position in relation to scene

4. 2 types of impressions:
Negative impressions – made by an object leaving a void in the substrate, i.e. stepping in a pool of blood and leaving a footprint in it
Positive impressions – made by an object leaving residue on a surface, i.e. leaving behind blood or dirt as one walks

6. Collecting impressions
Preferable to collect the original impression (i.e. on glass, paper, floor tile)
If the impression cannot be taken to the lab, a reproduction must be made.
Lifting tape
Casting dental stone
Electrostatic dust lifter
Snow-Print-Wax
Chemical developers

7. Lifting tape – use as with fingerprints
Use lifting material large enough to cover whole print
Good for lifting light dust or dirt
Dental stone – gypsum mix, like plaster, that hardens into a solid 3-D model

9. Electrostatic dust lifter –
Uses electrical charge and mylar sheets to create a static electrical charge that will lift dust/dirt marks
Snow-Print-Wax – used for casting prints in snow – creates a wax layer to protect the print from the plaster

10. Chemical developers –
As with fingerprints, ninhydrin and amido black can be used to enhance the appearance of prints.