Week 2 - Trace Evidence, Microscopy, Forensic Toxicology, and Forensic Chemistry

primary transfer

trace evidence that comes from direct contact with a source

secondary transfer

trace evidence that comes from an indirect source

why is context critical when analyzing trace evidence?

a lack of a trace doesn’t necessarily mean innocence, and a presence of a trace doesn’t necessarily mean guilt

goal of comparative analysis

to determine whether or not 2 samples came from the same source

exclusionary evidence

questioned (Q) and known (K) samples did not come from the same source

inclusionary evidence

questioned (Q) and known (K) samples may have come from the same source

function of stereo binocular microscope

2 single lens optical microscopes produce a 3D image, reflected light

formula for total magnification

objective lens * eyepiece lens

usage of a stereo binocular microscope

to locate and recover microscopic particles, preliminary evaluation of submissions

function of a compound binocular microscope

2 eyepieces but 1 2D image, transmitted bright-field illumination

function of polarizing light microscopy

polarized light enters a sample, gets bent, and passes through a different polarizer (analyzer). the rays recombine in the analyzer, causing interference which can be used to identify the substance

birefringence

difference between refractive indices of each direction of an object, can be used to identify a material

retardation formula

Retardation (nm) = birefringence* thickness of material (mcm) * 1000 (nm/mcm)