8127/frame/fm

Figure 5.1
Detection of blood with luminol.
What you see depends on how you
look. In this illustration, blood is invisible to the naked eye (top photograph),
but searching after applying luminol in a dark room reveals both the presence
and pattern of blood (bottom photograph).
8127/frame/ch04 Page 100 Friday, July 21, 2000 11:48 AM

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101
 
Recognition of 
 
Physical Evidence
 
Contents
A.
Evidence and the Law........................................................................... 101
B.
The Crime, the Crime Event, and the Crime Scene........................... 102
C.
What is Evidence? ................................................................................. 103
1.
The Search for Evidence ............................................................... 105
2.
The State of the Evidence ............................................................. 108
D.
Evidence and Reference ........................................................................ 109
E.
Summary ............................................................................................... 110
References ...................................................................................................... 111
The eyes see in things only what they look for, and they look only for what 
is already in the mind.
 
—Posted in the classroom of the School of Scientific Police at the Palais de 
Justice in Paris
Luke S. May,
 
 Crime’s Nemesis, 
1936
The most difficult challenge in the investigative process is the recognition of
 
relevant
physical evidence. Prior to any laboratory analysis, an item must be
recognized as evidence in a crime or it will never be examined, much less
interpreted. Ideally, the crime defines the relevant evidence. In this chapter we
will explore the attributes and circumstances that combine to make something
evidence and, in particular, physical evidence. We will also discuss the seem-
ingly obvious, but sometimes complex relationship between evidence and ref-
erence. We leave a detailed discussion of the crime scene itself to Chapter 8.