Other Impressions What other impressions can you think of at a crime scene?What other impressions can you think of at a crime scene? ShoeShoe TireTire FabricFabric ?????? How are impressions preserved?How are impressions preserved?

Lifting Impressions Two methods: 1) similar to lifting prints, 2) electrostatic liftingTwo methods: 1) similar to lifting prints, 2) electrostatic lifting 1.If made in light deposits of dust or dirt, place lifting material over impression, use fingerprint roller to eliminate air pockets, and lift impression.

2. Electrostatic Lifting (dust impressions) Electrostatic charge on comb and tissue paper exampleElectrostatic charge on comb and tissue paper example Mylar film placed over dust mark and pressed against impression with rollerMylar film placed over dust mark and pressed against impression with roller Electrostatic unit gives a charge to the film, attracting the dustElectrostatic unit gives a charge to the film, attracting the dust

2. Electrostatic Lifting (dust impressions)

Casting Impressions Class I dental stone (gypsum) is used to make casts of shoe and tire impressions.Class I dental stone (gypsum) is used to make casts of shoe and tire impressions. Cast needs to dry hours before transporting to the lab.Cast needs to dry hours before transporting to the lab. For snow impressions, spray with Snow Impression Wax, then pour Class I dental stone to make cast.For snow impressions, spray with Snow Impression Wax, then pour Class I dental stone to make cast.

Casting Impressions, cont…

Casting Impressions, cont… For shoe impressions in blood, the impression is “developed” and enhanced using various chemicals.For shoe impressions in blood, the impression is “developed” and enhanced using various chemicals.

Case Study O.J. SimpsonO.J. Simpson

Bite Marks How would bite marks differ from person to person? What are the odds of two people having the same bite marks? How are bite marks detected? –Visible –UV light

Bite Marks, cont…. How is evidence collected? –1 st step: –2 nd step: It’s like playing the game Operation. Ted Bundy