PHYSICAL SCIENCE IN THE CRIME-DETECTION 

 LABORATORY ^ 



By J. Edoab Hoover 

 Director, Federal Bureau of Investigation, V. 8. Depai'tment of Justice 



[With 5 plates] 



During the latter part of 1937 a police department in one of the 

 eastern States, in submitting to the Federal Bureau of Investigation 

 for laboratory examination a pocketknife and telephone cord, advised 

 that the telephone cord had been severed by a burglar in an effort to 

 delay notification of the authorities of the crime, and that the pocket- 

 knife had been recovered in the possession of a suspect apprehended 

 during the subsequent investigation. In addition to the examination 

 of other evidence forwarded at the same time, the police department 

 requested that an effort be made to ascertain whether the suspected 

 pocketknife had in fact been used to cut the telephone cord. 



Under the microscope there were observed on the cutting edge of 

 the knife blade minute bronze-colored stains. These stains were far 

 too small to permit their ready removal and identification by routine 

 chemical analytical methods. However, a spectrographic examination 

 of the cutting edge of the knife blade revealed the presence thereon 

 of the two chemical elements, copper and tin, which elements were 

 found by a similar examination of the back edge of the knife blade 

 to be elements not a part of the blade material itself. Inasmuch as 

 a spectrographic analysis of the telephone cord indicated that copper 

 and tin were the principal constituents of the severed conductor, this 

 information was immediately furnished to the contributing agency 

 for use in its further investigation and prosecution of the matter. 



During the early part of 1938 an examiner from the Bureau's 

 technical laboratory testified relative to his findings in the matter 

 before a court hearing the evidence against the suspect, as a result of 

 which, together with other evidence introduced at the trial, the sus- 

 pect was found guilty of the burglary and sentenced to a penitentiary 

 for a period of from 5 to 10 years. 



The above case illustrates, probably better than any other proof 

 which might be brought forward, the profoundly important part 



* Reprinted by permission from The Review of Scientific Instruments, vol. 9, No. 11, 

 November 1938. 



215 



