FORENSIC MICKOSCOPY 



scopic study after initial sorting from extra- or identification of the tool is made by com- 



neous debris is often a prelude to spectro- paring test marks made in a suitable manner 



graphic or x-ray diffraction analysis. on lead, wax, or other similar material with 



In some forensic examinations the micro- the original mark, or an accurate reproduc- 

 scope plays an ancillary role; in others it tion, from the crime scene. In making this 

 plays a major part in the examination. It is comparison, such variables as the hardness 

 significant that through the microscope the of the material, speed of the operation, and 

 possible source of a specimen of hair on a the angle of the work surface to the test 

 murder weapon can be determined, blood- piece must be controlled and altered sys- 

 stains found on the clothing of a suspect can tematically until the right combination pro- 

 be typed, seeds transported from a crime duces what is termed, a "match", 

 scene can be identified, dust contaminating Each tool-mark will possess certain defi- 

 the clothing of a burglary suspect can be nite characteristics which will identify the 

 evaluated, and many more possible clues to type of work operation performed by the 

 the perpetrator can be studied. The impor- tool, that is to say, the mark may be the 

 tant contribution of microscopy to the medi- result of straight compression or it may be 

 colegal determination of the cause of death the result of some sUding or cutting action 

 through the histological study of various by the tool. The gross dimensions and gen- 

 tissues removed at autopsy is well estab- eral appearance of the tool mark will suggest 

 Ushed. the type of tool that is involved and these 



Since most of the microscopic methods would be called class characteristics. Dis- 



employed in the forensic field are either tributed throughout the tool mark will be 



standard methods, or adaptations of stand- fine striations of a more or less microscopic 



ard methods, they need not be discussed in nature which will represent the individual 



detail here. One examination procedure not characteristics of the tool-mark which will be 



commonly found in analytical laboratories, the basis upon which an identification is 



yet frequently used in criminalistics, is com- ultimately made. 



parative micrography. By the use of the The requirements of a "match" are met 



comparison microscope, tools are related to when the gross dimensions and appearance 



marks left at the scene of a crime, bullets and the fine striations or individual charac- 



and cartridges to firearms. The first of these teristics are sufficiently ahke to permit an 



applications is called tool-mark comparison, experienced technician to render an opinion 



and the second is referred to as firearms that the same tool made both test and evi- 



identification. Like many other areas of dence marks. Although the identification is 



laboratory endeavor, these fields are part art, based upon fundamental principles of proba- 



part skill, and part science. bility, the work in the field of comparative 



Basically, the identification of a tool as micrography has not progressed to the point 



responsible for an evidence or a crime scene of feeding sufficient individual identity data 



mark is possible only because each tool has into a formula and producing, automatically, 



many randomly situated, microscopic im- a determination of positi^'e identification, 



perfections that are not duplicated, even by The merits of the decision must be weighed 



machine production, on any other tool or against the skill and experience of the tech- 



workmg surface. These minute imperfections nician in each and every identification, 



are then transferred to any materials softer An example of tool mark identification is 



than the working edge, leaving on the sur- shown in Figure 1, where a comparison is 



face what is equivalent to a fingerprint of made between a drill bit mark in lead, as the 



the tool that was used. The final comparison standard, and a silicone rubber reproduction 



339 



