Tool marks and impression evidence

Positive comparison

A cast is made of the scratch marks left on the window lock from force entry. result can be a positive comparisons and chance a definitive ass. of the tool with a sufficient quantity of striations match between evidence and test mark

Tool marks

Are made when a harder object come in contact/ a softer object leaving marks

Packaging

suspect tool and mark must be packaged separately

Never

attempt to fit the suspect tool in the tool mark may alter the mark or raise serious questions about evidence

impression

can be discovered in the most unusual places

careful examination

can reveal class characteristics rarely any significant individual characteristics that could permit the examiner to individualize.

photograph mark

clarity of many of the tool mark's minute detail will be lost or obscured in photo or cast

mayor problem

comparison is the difficulty in duplicating in the lab the tool mark test at the scene

Found where

encountered at burglary scene that involved forcible entry in a building

dental stone

fine grade of calcium sulfate that was developed for dentist take dental impressions

trace evidence

greatly enhances the evidential values of the tool or its mark and requires that special care to be taken in packages and handling to avoid the loss or destruction of theses items

striations

if the edge of a tool is scraped against a softer surface it may cut a scenes of striated lines that reflect that pattern of the tools edge. Marks left in this manner are compared in the lab through a comparison microscope with test tool marks made with tool.

imperfections cause individually

it is the presences of these minute imperfections that imparts individuality to each tool.

microscopic irregularities

machined surfaces of a firearm are impressed w/ random striations during manufacture the ages of a dry bar chisel, screwdriver, knife and cutting tool

machining process

marking are left gas a result of machining processing used to cut and finish tools These marks are called striation marks Screwdriver is 1st made microscopic imperfections in a blade make it unique

Test marks

through comparison requires the preparation of a series of test marks obtained by applying the suspect tool at various angles and pressures to soft surface

Casting

used liquid silicone or dental stone