28 
etc., are examples. A good working rule is that' every¬ 
thing is to be held as a clue which can not be accounted 
for without reference to the offense. While all things 
unaccounted for are clues, they do not become evidence 
until their connection with the action of the suspect is 
clearly shown. 
Some things, such as tracks, the forest officer can inter¬ 
pret better than any outside expert—in other words, he 
is himself the best expert. Other things can only be 
interpreted by those with special training; for example, 
the microscopist, the chemist, or other specialist. Not 
even the smallest thing is unimportant until it is certain 
that it has no useful connection with the case. 
The working theory .—To guide the investigator in the 
interpretation of clues or evidence two things are neces¬ 
sary: (1) Every bit of knowledge he can gather before 
leaving for the scene or on the way, as to the offense, 
including its occurrence, surrounding circumstances, and 
probable author and motive; (2) the building of a mental 
picture or reconstruction of all that he knows of the case. 
This must be constantly building and constantly revised. 
Nothing else will prevent wandering, loss of time, and 
possible failure. At the start it may consist only of a 
“hunch” as to who set the fire or where to look for clues; 
but every new thing found will contribute to it. This 
mental reconstruction or theory of the case is the indis¬ 
pensable bridge by which to cross from the initial clue to 
the completion of the case. 
How to search .—On arriving at the scene first locate the 
critical point; for example, the origin of a fire. If the 
point of origin is not evident, beware of jumping to con¬ 
clusions; the incendiary or other criminal does not do the 
obvious thing if he has sense. Then examine minutely 
the immediate area. System is absolutely necessary in 
this search. Go carefully around the point of investiga¬ 
tion, widening the circles each time, but keeping them 
close enough together (say 3 feet apart at first) to make 
sure that every foot of ground is minutely examined. 
Drop markers to show where each circle ends. 
