Each ridge of the fingers, palms, and soles bears a row of sweat pores
which in the average person constantly exude perspiration. Also, the
ridges of the fingers and palms are in intermittent contact with other
parts of the body, such as the hair and face, and with various
objects, which may leave a film of grease or moisture on the ridges.
In touching an object, the film of moisture and/or grease may be
transferred to the object, thus leaving an outline of the ridges of
the fingers or palm thereon. This print is called a latent impression,
the word latent meaning hidden, that is, the print many times is not
Latent impressions, regardless of the area of the ridges present, are
of the greatest importance to the criminal investigator as
identification of them may solve the crime and result in successful
prosecution of the subject. Consequently, every effort should be made
to preserve and identify them.
Visible prints in mediums such as blood, grease, dirt, or dust are
equally important to the investigator but, strictly speaking, are not
A search of the crime scene should be conducted in a logical manner.
Points of entry and exit should be examined, along with surfaces or
objects disturbed or likely touched during the commission of the
crime. The examiner should wear a pair of light cloth gloves and
handle an object only insofar as is necessary and then only by edges
or surfaces which are not receptive to latent impressions. A record of
the exact location of a print on an object and of the object itself
should be made, since these facts may be of the utmost importance in
any trial resulting from the investigation. No one should handle an
object other than the examiner himself.
Portable articles removed should be labeled or marked so that they may
be readily identified thereafter.
The beam of a flashlight played over the surface of an object will
frequently show the location of latent impressions, although this is
not an infallible test for their presence.
Evidence should be examined as soon as feasible after its discovery.
Following the location of any latent prints at the scene of a crime,
the prints of all persons whose presence at the place under inspection
has been for legitimate purposes must be excluded from further
attention. It is advisable, therefore, during the initial stages of an
investigation where latent prints are found, to secure the inked
prints of all members of the household, the employees, and any police
or other officials who may have touched the objects on which the
latent impressions were found. Inked prints taken for this purpose are
referred to as elimination prints.
Due to the fragmentary nature of most latent prints it is not possible
to derive a classification which makes a file search practicable. A
latent impression may be identified, however, by comparison with the
prints of a particular suspect.
Inked fingerprints taken for comparison with latent impressions should
be as legible and as complete as possible, including the areas not
essential to classification, since identifications are often made with
these areas. Inked palm prints taken should likewise be complete and
clear and should include impressions of the finger joints. Persons not
experienced in latent print comparisons should not attempt to evaluate
latent fragments, since the area necessary for an identification may
be extremely small compared to that of an average inked fingerprint.
Articles which are to be transported by mail or express should be so
packed that the surfaces bearing latent impressions are not in contact
with other surfaces. This may be accomplished by mounting the articles
on a piece of fiber board or plywood. The board should then be secured
in a box so that the objects will not touch or be shaken against the
sides in transit. The package should be plainly marked Evidence, to
prevent inadvertent handling on opening. Cotton or cloth should never
be placed in direct contact with any surface bearing latent prints.
Any number of paper or cardboard specimens may be placed in a single
protective wrapper, since contact with other surfaces does not harm
latents on such objects. Lifts, negatives and photographs are readily
enclosed with letters.
An explanatory letter should accompany all evidence. If it is
necessary to pack the evidence separately, a copy of the letter should
be placed in every package so that the recipient will know immediately
the import of the contents. All items of evidence should be marked and
described exactly in the accompanying letter so that they will not be
confused with packing material of a similar nature, and to provide a
check on what the package should contain.
In addition, the letter should include for record purposes a brief
outline of the crime, i.e., type, date and place of occurrence, and
names of victims and subjects. If suspects are named for comparison,
sufficient descriptive data should be set out to permit location of
their fingerprint records. This information, in preferential order,
comprises the individual's complete name, aliases, FBI number, date of
prior arrest or fingerprinting, fingerprint classification, date and
place of birth, and physical description.
Evidence is preferably forwarded by registered mail or railway
express, as these means provide records of dispatch and receipt.
Elimination or suspect fingerprints are best enclosed with the
evidence itself, with a notation as to the type of prints forwarded.