In movies they always show bodies shapes at a crime scene drawn in chalk. Did they really used to do that or is that Hollywood. Wouldn't it contaminate the crime scene?
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Some counties use this type of marking to outline certain types of evidence "YES"....others use invisible flourescent spray tubes, some use painters blue tape while others use Contractors yellow Crayon....and some use an opaque white Crayon type marker.....the reason for using the waxy types of markers is that they can be washed away with alcohol or paint thinner, Chalk with water, and the invisible flourescent?....it stays around awhile and it shows up under black light.