348 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1954 



perforated cards. Efficiency is, as a result, several thousand times 

 greater than before. A search which used to take several hours can 

 be completed in a few minutes. This system has been developed en- 

 tirely by mathematical reasoning based on the theory of sets, though 

 a large number of statistical calculations with computing machines 

 were also necessary. It is a very clear and recent example of the ad- 

 vantages of using a scientific method, in this case associated with a 

 complicated branch of mathematics, in what seemed to be a totally 

 unrelated field. 



Before leaving this matter, we must point out that it is impossible 

 for the police to trace an individual in a big 10-finger filing system, 

 when they have only more or less perfect prints of one, or even two or 

 three of his fingers. At the scene of a crime or a burglary, fingerprints 

 are very often found on objects that the criminal has handled, and most 

 people believe that the perpetrator of the crime can be identified, by 

 reference to these prints, simply by looking through the files. This is 

 not so. If an individual is to be found in a big 10-finger filing system, 

 we must have prints of all 10 fingers. On the other hand, to identify 

 a finger which has touched a glass and left a print on it, one has simply 

 to compare the print and the finger ; very often the identification is a 

 mere formality. For this to be feasible, however, we must suspect a 

 particular individual and have his fingerprint card. Comparison of 

 each of the prints on the card with that found at the scene of the crime 

 will enable us to say whether the latter was made by one of the fingers 

 on the card. There are also single-finger filing systems from which, 

 in certain cases, an offender can be traced by the ridge marks he may 

 have left at the scene of the crime. 



PHOTOGRAPHY 



Criminals leave behind them not only their fingerprints but also 

 many other material traces which, if properly collected, studied, and 

 interpreted, may enable us to reconstruct events exactly as they hap- 

 pened and to identify the person responsible. This principle is the 

 very foundation of scientific detection, and the first function of this 

 science is to discover such traces and study them in the laboratory, in 

 order that they may be used in evidence. 



First and foremost, the state of the scene of the crime immediately 

 after the event nvust be permanently recorded, and for this purpose 

 photography is naturally used. The importance of the documentary 

 evidence thus obtained is well illustrated by the following example. 



A murder is committed, the victim being killed by two bullets in 

 the head. Our service is not informed until the following day, when 

 it takes photographs of the scene of the crime. No trace of a bullet 

 can be seen. A week later, in company with the examining magistrate. 



