A knife is found at the scene of a crime. Whose knife is it?
An ingeniously devised bomb is discovered. Who made it?
A burglar makes an entrance by means of certain tools. A suspect is arrested, and in his
possession are found tools that might have been used for this purpose. Can the criminal
investigator prove that these tools were so used?
From the days of Vidocq, who organized the first detective bureau in Paris at the
beginning of the last century, until the present time, such questions have been answered
largely by means of adducing circumstances, espionage, and reports of witnesses. In
other words, the human element has played a major role in crime detection, and perhaps,
always will.
Yet, how notoriously unreliable are the
human factors! How many murderers have
escaped the gallows because the authorities were unable to prove their guilt! How many
innocent men have been imprisoned or hanged because people made mistakes either in
identification or in reporting circumstances of
the crimes committed!
No two eyewitnesses of a particular episode will make identical reports. What each sees
is influenced by so many factors. A state of excitement or terror will distort the true
picture. Memories are notoriously faulty. A small man dressed in white and seen in the
dark will appear very tall. An ordinary object suddenly seen in the dark will appear
immense. A medium-sized man dressed in a black suit will appear tall to the casual
observer. If a strange object is seen for the first time,
the observer will have no previous
knowledge of its true nature, and hence optical illusions will lead him astray. Let an
African savage view a railroad track for the first time and he will report that the rails
meet in the distance. A house on a hill look
s hardly large enough to accommodate a dog.
Few people can accurately judge distances or dimensions. Many people fail to judge
accurately from whence a sound comes, whether from below or from above; from the
right or from the left. A wounded man or one immediately at the scene of the crime may
be the most untrustworthy witness of all; for such persons often experience
hallucinations, both visual and auditory.
Many witnesses lie without malice. Vanity may prompt some to fill in gaps in their story
from pure
imagination. Other witnesses may be moved by a mistaken zeal to be helpful to
the investigator and report their own deductions and opinions as actual facts. Another
may have an enemy whom he wishes to implicate, and the wish becomes the father of the
report he gives—almost unconsciously sometimes.
From such flimsy threads the investigator must often weave the net that captures the
criminal! Wonder it is that he succeeds as often as he does!
