31 
There is no time to be wasted, but right interpretation of 
facts and right action respecting them are so essential 
that the time necessary to insure these will yield bigger 
dividends than undue haste. Moreover, most of us find 
general instructions so difficult, to apply to concrete cases 
that it requires specific and conscious effort; but to do it 
is a constant necessity until one becomes very familiar 
with the instructions. Most of the past failures in law 
enforcement have been on points directly covered by 
unheeded instructions. No instructions are beyond 
improvement; but every investigator will be held responsi¬ 
ble for following them, unless other action is proved better 
by actual results. 
With respect to the working theory, the simplest one 
which will explain the facts is always preferable; but 
the theory is never complete until the case is closed. 
At all times, but especially at first, when the theory is 
based on few facts, it must be lightly held, subject to 
modification at any time by what shall be discovered 
next, regardless of whether the new evidence agrees with 
the previous theory or not. 
Such open-mindedness, viewing every new fact on its 
own merits, is harder to maintain than many people 
suppose, and requires constant and definite effort. It is 
extraordinarily easy to overvalue new facts which coin¬ 
cide with the theory already built, and to undervalue those 
which do not. Nothing is more fatal to success or more 
common among inexperienced investigators than a pre¬ 
conceived theory which its holder will not change when 
evidence contrary to it appears. Therefore it is neces¬ 
sary every little while to review one’s theory systemat¬ 
ically in the light of all facts. Especially beware of 
believing that any given man could not have set the 
fire—believe your evidence; in investigation reverse the 
legal rule and believe anybody guilty until he is proved 
innocent. Beware of thinking the criminal could not 
have made so big a blunder, when such apparently 
develops—he usually does blunder somewhere, otherwise 
he would never be caught. 
42956—23-3 
