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Poor Impressions

Poor impressions usually are caused by one or more of the following mistakes:

1. The use of poor, thin, or colored ink resulting in impressions too light or too faint or with obliterated ridges. Best results are obtained by using heavy, black printer's ink. This is a paste, and it should not be thinned before using. It dries quickly and does not blur or smear in handling.

2. Failure to clean the person's fingers thoroughly before inking. If foreign matter (or perspiration) adheres to the fingers, false markings appear and characteristics disappear.

3. Failure to clean the inking apparatus after each use.

4. Failure to roll the fingers fully from one side to the other and failure to ink the entire finger area from tip to below the first joint. Such failures result in important areas not appearing on the print. The impression should show the entire finger, from the first joint to the tip, and from one side to the other side.

5. The use of too much ink, resulting in the obliteration of ridges. Just a touch of the tube of ink to the plate is sufficient for several sets of prints. It must be spread with a roller into a thin, even film.

6. The use of too little ink, resulting in ridge impressions too light and too faint for tracing or counting. If light or faint impressions occur when using a porelon pad the pad needs to be replaced.

7. Slipping or twisting of the fingers, causing smears, blurs, and false patterns. Hold the fingers lightly, using little pressure, and caution the person against trying to help. Ask him or her to remain quiet and relaxed.

By following the foregoing instructions closely, you can make clear fingerprints that can be classified quickly and accurately. In police work, it is often important that fingerprints be classified quickly for identification. Identification cannot be made quickly, however, if the quality of the prints is unsatisfactory. Make the prints right the first time!


The first law enforcement personnel to arrive at a crime scene must be "fingerprint conscious" and protect the scene to pevent fingerprint or other fragile evidence destruction until the scene can be processed. Persistence, determination, and imagination by the crime scene investigator will be most rewarding.

All persons not absolutely necessary to the conduct of the investigation should be excluded from the area of the crime scene to prevent inadvertent destruction of evidence.

Finding Fingerprints

Many uninformed persons have the mistaken belief that an attempt to obtain prints would be unrewarding and unsuccessful because of the physical nature of the object, or the object having been subjected to adverse conditions. Intelligent and persevering attempts to obtain prints and other trace evidence should be made under all circumstances. Smudges that have been left by fingers having grease, blood, or other foreign substances on them, but lack ridge characteristics, are not serviceable as latent prints. However, they should at times be considered as other types of trace evidence.

Latent prints fall into three general classifications: (1) visible prints made by a finger coated with a foreign substance such as blood, grease, dirt, and so forth, and plainly visible; (2) plastic impressions found impressed in pliable substances such as butter, candles, putty, and semidry paint; and (3) invisible or semi-invisible prints made by natural body secretions on the hands and fingers.

Visibility of latent fingerprints depends upon the physical condition of the person leaving the print, surface of the object, angle of reflection of the light by which they are viewed, time elapsed since they were placed, amount of heat to which they have been subjected, and other factors.

The amount of time they will remain on an object is also to some extent dependent upon atmospheric conditions, air currents, and humidity.

It is logical to start the examination of a crime scene for fingerprint evidence at the point of entry. Other possible points of entry should not, however, be overlooked since futile attempts may have been made there. The search continues in the same manner as for other evidence.

A strong oblique light is a great aid to the investigator in discovering latent fingerprints.

Always note exactly where latent prints are found and their location on the object on which they are found The angle they assume might indicate how an object was held or what position the hand was in when the print was made.

Sometimes, when picking up a heavy object located close to a wall, one will place a hand on the wall as a brace. This location should not be overlooked when processing a crime scene. The same applies to countertops and other flat surfaces upon which a subject may lean without actually moving the object.

The undersides of heavy objects such as tables, chairs, and other furniture should not be overlooked as possible sources of latent prints since it is natural for finger contact to occur when lifting or moving them.

Numerous prints may be found at the scene and all should be preserved-any unneeded ones can be discarded later.

A notation as to exactly where the latent print was found, its position, when it was found and by whom are most important points to record. Any slight mistake by the investigator, when testifying in court, might result in the elimination of the evidence from consideration.

When a latent print is frond, the first-always the first-thing that must be done, is to photograph it. Various photographic techniques consisting of reflected light at various angles, falters, and different types of film may be required to obtain a photograph of value.

The use of back-lighting through a pane of glass has been very successful with the faintest of latent prints.

Cameras having a fixed focus and termed fingerprint cameras are not available through supply channels and should be ordered as an open purchase item. A view camera is most versatile. By being able to see the latent print through the camera lens under varying conditions of light, the investigator can determine the best procedure. By stopping the lens down, good readable prints can be obtained from curved surfaces with the view camera. This type of camera is highly recommended.

Also, always include a ruler in photographs of fingerprint evidence.

After a print has been photographed other methods of preserving the print maybe attempted

Visible prints made with some foreign substance on the fingers can often be lifted with fingerprint-lifting tape. If these types of latent prints, as well as the plastic type of latents are on small objects, the entire object may be retained and held as evidence.

Latent prints made with just the normal secretions of the skin will usually have to be processed in a special way before they can be of any real value. Perspiration is about 98 percent water with the remaining percentage composed of fatty acids, urea, sodium and potassium chlorides, phosphates, carbonates, sulphates, lactic acid amino acids, and traces of many other substances. These substances lend themselves to various types of treatment. The most frequently used processes are powdering and chemical treatment.

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