The Reproduction of Shoeprint and Tiretread Impressions
FBI Law Enforcement Bulletin, June 1947
The officer conducting a crime scene search must be alert for evidence which will identify the suspect as having been present at a particular place, and, if possible, identify him as having been there at a particular time.
The experienced investigator conducts such a search with full knowledge of the importance of the smallest detail. His investigation, therefore, is methodical and exacting. He knows that a chain of evidence may solve a crime, and that he must not overlook a single link. For this reason he does not underestimate the value of preserving tire and shoe prints for he knows they may be the surest evidence 1eadirig to the criminal.
FBI Shoeprint and Tiretread Files
The Federal Bureau of Investigation has, with the cooperation of tire and shoe manufacturers, assembled thousands of tire and rubber footwear patterns and designs for reference in criminal investigations. Too voluminous for copy and distribution, these files are maintained in the FBI Laboratory, available for ready reference to all law enforcement agencies.
The Tiretread File represents an attempt to obtain and keep current, blue prints of tread and sidewall designs produced by tire manufacturers throughout the country. The blue prints contain exact specifications for each tire. When a photograph, plaster cast or sketch is identified as a particular brand, it is possible to report to the contributor the tire's size, brand, manufacturer, and distributor.
The Tiretread File also contains retread and recap designs currently in use. It is frequently possible to determine whether a print has been formed by a recapped or retreaded tire. However, any design may be reproduced in recap or retread work and therefore the possibility of a print having been produced by a recap or retread should not be overlooked. The latitude of recap and retread companies is great. They often develop their own original designs. Knowledge that a design is peculiar to a locality may be valuable in an investigation where such a tiretread is involved.
The Shoeprint File contains designs, trade marks and other insignia which appear on rubber heels and soles manufactured by companies in the United States. When the Laboratory identifies a questioned print with a particular pattern, the contributing agency is furnished with complete information as to the size, manufacturer, distributor, and, if available, data as to whether the heel or sole is distributed for repair work or to be used on new footwear. In addition, a photograph of the sample heel or sole on file is furnished for the contributor's investigative assistance.
Examination of Evidence
Shoeprint and tiretread examinations are generally of two types. One is to determine the design, size and manufacturer of a shoe or tire as the case may be. This requires a complete search of the questioned material through the Shoeprint or Tiretread File. The information developed may be of value in the investigation of a case. The other type involves the examination and comparison of a tire or shoe belonging to a suspect with a cast or photograph reproduced at the scene of a crime in an effort to make a positive identification. The latter type mentioned is more important from a standpoint of actually connecting a suspect to the crime.
Style characteristics enable the examiner to determine only the brand of tire or shoe. In order to identify a print as having been made by a particular shoe or tire, there must be characteristics present on the original evidence Which are peculiar only to it. These may be cuts, bruises, tears, or manufacturing defects and the examiner must decide on the basis of their presence whether they are sufficient to establish a positive identification.
In a recent case three different style tire treads were found ..at the scene of a .crime. Plaster reproductions of these prints were forwarded to the FBI Laboratory where, upon comparison in the Tiretread File, they were classified as . to trade name. This information was reported to the contributor. In the course of the investigation, the car of one of the leading suspects was found to have tires corresponding to the makes of the prints in question. The suspect's tires were then submitted to the Laboratory with the request that they be compared with the plaster casts. As a result of the comparison, the Laboratory was able to positively identify one tire as having caused the impression reproduced by one of the plaster casts. The o t ~ e r tires did not contain sufficient identifying characteristics to positively identify them with the remaining casts. However, it was possi ble to determine that the design and size of these two tires corresponded exactly with the other two cast impressions. This examination materially assisted the prosecution in the adequate court presentation of the case.
Procedure
The exact procedure to be followed in a particular case may be dependent upon circumstances peculiar to that case alone. The suggestions set forth are given for consideration itl an average case. It is well to remember that the success of each examination is dependent not only on the questioned print's clarity, but also on the investigator's ability to reproduce such evidence properly.
Photography
Frequently a photograph is the only satisfactory way to reproduce the original evidence. Extreme care should be taken to insure the best results.
Generally speaking, all photographs will present a truer picture if the camera opening is stopped down and a corresponding longer exposure used. The smaller aperture opening will bring more of the vital area into sharp focus. Special photographic equipment is not necessary in photographing shoeprints or tiretreads and experience has proved that standard equipment will produce excellent results.
The investigator should first consider the desirability of taking a distant photograph of that portion of the scene bearing the shoeprint or tiretread in order to orient it with respect to the crime, and tie it into the picture of the surrounding area. Such a photograph, if possible, should not include any object foreign to the original crime scene itself, but should represent a true picture of conditions as they prevailed when the print or impression was first discovered.
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If several impressions of each shoe or tire are present, it is well to consider the advantages of photographing and reproducing more than one impression of each in order to obtain as complete a representation of the original shoe or tire as can be had. With two or more prints of the same object, even though .they may be fragmentary, a complete composite picture might be obtained. Peculiarities are repeated in additional prints if they exist on the original tire or shoe, whereas if they were dependent upon foreign substances on the ground or receiving surface, they would not be repeated in identical detail. While photographing a particularly long tiretread impression for examination purposes, it is better to take two or more closeup pictures of the impression and have them overlap, rather than take one picture of the entire impression at a greater distance and lose considerable detail necessary for possible identification.
Before the closeup photograph is taken, the print or track should be examined to determine whether any loose particles or foreign material have fallen into the impression. Such particles may cover important identifying portions of the impressed pattern and thereby eliminate them from the photograph. They should be removed without disturbing the impression itself.
In order for the Laboratory Examiner to arrive at a conclusion as to the size or identification of a particular track from a closeup photograph, it will be necessary for him to have an accurately scaled and well-lighted picture. This should be taken at a perpendicular angle with a ruler or scale placed in full view alongside the impression to be photographed. An exactsize photograph of the original impression may be printed to assist the examiner in his comparison. This scaled photograph will also aid in court presentation of the evidence. A small slip of paper containing 1n1tials, date and other identifying data should also be included in the photograph. By using a source of light from one side of the impression only, shadows are formed which will bring out detail. Either real or artificial light may be used in this manner. Flash equipment available for most standard cameras can be used to advantage here by detaching the flash gun from the camera and holding it to the side of the impression being photographed.
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Photography is of paramount importance in the examination of two-dimensional prints such as a shoeprint in dust where it is not possible to reproduce the impression by use of a cast. Side lighting, as previously mentioned, should be used for best results. However, when it is possible, the article containing the print should be submitted to the Laboratory where the original can be examined and photographed to a better advantage. One recent case involved the examination of a faint dust print of a heel appearing on a piece of window glass. This print was barely distinguishable to the naked eye. Only after photographing was it possible to identify the make of heel and so inform the contributing agency.
Preparation of Casts
Obviously, in photographing evidence as described above, only two-dimensional reproductions will be obtained . This has certain limitations as compared with a three-dimensional cast. The cast is an exact reproduction of the original evidence and is therefore important for comparison purposes. The investigator has only one chance to make a good cast for the impression is completely destroyed as soon as the finished cast is removed.
After the impression has been photographed, proper preparations should be made for casting . A print found in moist, firm earth can be reproduced with little difficulty. However, when prints are found in sand or loose loam, it is advisable to spray them lightly with a fast-drying shellac to make the impression firm enough to withstand the plaster when it is poured. A household spray gun may be used for this but care should be exercised to keep the direct force of the spray from disturbing the impression.
A thin, insulating layer of talcum powder over a track will aid in making a cast of an impression found in snow. The talcum powder will tend to prevent the heat produced by the hardening plaster from melting the snow. A fine wire screen may be used to sift the powder and insure even distribution over the print.
Plaster of Paris is the most practical medium for making three-dimensional footprints and tiretread reproductions for law enforcement purposes. It is inexpensive, easily obtainable at hardware and drug stores, and, if the finest grade of art or dental plaster is used, the resulting case will be smooth and non-flacking.
Plaster of Paris is so simple to use that the investigator may become quite proficient after a few practice attempts. Water and a container in which to mix the plaster are the only other materials needed.
After making a generous estimate of the amount of water required to fill the impression, place the water in the receptacle and add plaster of Paris slowly. The mixture should be stirred constantly until it has attained the consistency of rich cream or pancake batter. Another method used to obtain the proper mixture is to sprinkle plaster of Paris on the surface of the water allowing it to sink to the bottom spontaneously. When the water is unable to absorb more plaster the mixture should be stirred thoroughly and then poured. This method of sprinkling plaster on the water has been used to cast impressions already filled with water by rain, etc. However, the suggested procedure in this case is to drain off or soak up the water before attempting to make a cast, if it is possible to do so without disturbing the impression.
The plaster should be poured into the impression slowly and evenly at first, and with one complete motion, over the entire pattern. After about t inch of plaster is poured, a reinforcement of twigs, sticks or mesh wire or similar material may be placed on the plaster to give the cast increased strength. The remainder of the plaster should be poured quickly over the reinforcements.
In pouring a cast sufficient plaster should be used to make a very thick reproduction even if it is necessary to build up a retaining wall of wood or cardboard around the impression to keep the plaster from spreading before it sets.
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Before the plaster of Paris is completely hardened , the back of the cast should be marked and dated in some manner to permit future identificat ion which will assist in the examination and also aid in court testimony. A casting requires approximately 20 to 30 minutes to completely harden, depending upon its size and bulk.
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Caution should be exercised in cleaning the print surface of the casting after it has hardened and has been picked up. Nothing should be used to remove the dirt that might injure the casting or deface any of the print design. The best method is to clean by washing gently in water or by holding it under a low pressure stream of water for a short time. The water action will generally loosen all adhering dirt particles with out affecting the cast surface if a good quality of plaster has been used and allowed to fully harden before cleansing.
Other Uses of Casting
Occasionally a law enforcement agency is called upon to reproduce death masks, perishable food, wounds, and other evidence which present a problem different from reproducing tiretreads and shoeprints inasmuch as it is usually necessary to first make a negative mold using specially prepared moulage materials. These moulage materials are generally available at art supply stores. Utilizing the negative mold a positive cast is then made out of plaster of Paris or wax material as desired. This step corresponds to the reproduction of tiretreads or shoeprints by plaster casting.
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Mailing Casts
When forwarding plaster of Paris casts by parcel post or express every effort should be made to pack them carefully. A number of casts received in the FBI Laboratory for examination are broken and in some cases are in such condition that an adequate examination cannot be made. First, each cast should be wrapped separately in several layers of tissue paper or other soft paper and then wrapped and sealed in heavy wrapping paper. The parcels may then be loosely packed in plenty of cotton, excelsior, shredded paper or other shock absorbing material placed in a suitable rigid shipping carton or box. The container should be clearly labeled and stamped to indicate that the contents are fragile. It is also well to include with the cast all photographs that may be of value in the examination together with a copy of an explanatory letter.
Summary
Let us summarize briefly by listing the steps to be taken in preserving and transmitting shoeprint and tiretread reproductions.
1. Photograph- Entire scene of crime showing questioned impressions.
- Closeup of questioned prints properly identified and scaled.
- Collect materials (plaster of Paris, water, container for mixing, reinforcements).
- Mix plaster to thick cream consistency.
- Pour plaster slowly and evenly about t inch thick.
- Reinforce with sticks, twigs, or mesh wire.
- Pour remainder of plaster over reinforcements.
- Identify cast before it is completely hard.
- Remove and clean cast with caution.
- Wrap casts separately and identify properly.
- Pack casts loosely with cotton or excelsior in sturdy container. Include photographs and cover letter.
- Wrap container and mark "Fragile."
- Forward by parcel post or express to the Federal Bureau of Investigation, Washington, D. C., "Attention FBI Laboratory."
- See "Photography and Its Application in National Defense" from FBI Law Enforcement Bulletin of May-June, 1942; also "Photographic Work of FBI," ibid., January, 1946.
- See "The Reproduction of Original Evidence in the Third Dimension" from the November 1936 issue of the FBI Law Enforcement Bulletin.