Abstract: Footwear impressions are commonly found at a crime scene, potentially linking a suspect to that scene. The time that elapses between the collection of impressions from the scene and collection of the suspect’s footwear, however, can sometimes be weeks or months. The question then arises as to how much change in the soles’ patterns should be expected over a given amount of time. The purpose of this study was to investigate what is to be expected in a two-month delay in the collection of known samples from a suspect. This study demonstrates that even after two months of wear the possibility exists for a shoeprint identification.

Introduction

Questions concerning the time elapsed between the collection of shoe impressions at the scene and the collection of a suspect’s shoes are commonly heard by shoeprint analysts. A review of the literature has failed to uncover previous studies that attempted to answer these questions. It is not known exactly how much time can elapse before identification is impossible between a questioned impression and a suspect’s shoe. It is dependent on several factors such as how often the shoes are worn by the individual and what surface is stepped on. Obviously, someone walking on rough surfaces will acquire more marks on the bottom of his or her shoes in less time than someone who is always walking on a smooth, carpeted surface. An analyst performing shoeprint identification can expect some differences between the questioned impression and the suspect’s shoe if there was any significant interval between the time the impression was made and the shoe was confiscated. The degree of difference, however, is dependent on what occurred between those two events. Shoeprints can be linked to a person’s shoes by comparing such general characteristics as the shoe’s class characteristics, wear pattern, and individual characteristics.

Class Characteristics

Class characteristics are marks that are a direct result of the manufacturing process of the shoes [1]. These marks may be intentional or unintentional. The important fact to remember is that they are repeated on the sole of each shoe that is made. For instance, an athletic shoe will have a certain tread design on its sole. Most athletic shoes that are made these days have their tread pattern designed by a computer program using modern CAD-CAM techniques [2]. This generates a computer file that produces a mold of the same design every time. This mold can then be altered, thereby individualizing it from other molds. For example, a worker can repeatedly hammer one area of the metal mold to produce a stippled region. This imparts a random texture onto the metal mold. Another alteration that is commonly seen is the interchanging of logos so that more than one shoe company can use the same mold. This is important because it individualizes each mold. The mold subsequently forms the rubber into the shoe outsole and thus each shoe produced from that particular mold will be identical when new.

Wear Patterns

Wear patterns are defined by Bodziak as the erosion of the outsole due to frictional and abrasive forces that occur between the outsole and the ground [1]. Over time, these abrasive forces wear down the material on the bottom of the shoe, resulting in a lack of, or alteration of, the original sole design in certain areas of the shoe’s sole. Wear patterns play an important and underutilized role in the analysis of footwear impressions. The degree of wear is important in comparisons when there is significant difference between the shoeprint and the questioned shoe. Another important factor in wear patterns is the position of the wear. Pronated feet will strike the ground differently than supinated feet, causing the wear pattern to be different. A pronated foot strikes on the inner portion of the shoe sole, and a supinated foot strikes on the outer portion of the shoe sole.

Individual Characteristics

Individual characteristics are random nicks, cuts, or slices on the shoe’s sole that make a particular sole unique and thus identifiable [1]. A shoeprint examiner is commonly asked how many of these individual marks are needed for a true identification of shoeprints. Just as in fingerprints, there is no simple answer to this question. Although both involve pattern matching, footwear comparisons are different from fingerprint comparisons because of their very nature. Fingerprint comparisons involve the pattern and interrelation of bifurcations, ending ridges, and islands [1]. Shoeprint comparisons not only take into account a myriad of ever-changing manufactured sole designs, but also individual wear patterns and unique markings in sole impressions. In shoeprints, an infinite number of different cuts or slashes can occur. Compounding this fact is the amount of detail within each slit, chip, nick, or cut. A wide gash can have variances along its ridge, making it different from another wide gash. Therefore, it is up to the analyst to determine whether there is sufficient uniqueness to the individual characteristics of a shoeprint for identification. An impression with relatively simple individual characteristics will require a larger number of marks to establish uniqueness. On the other hand, an impression displaying complex, irregular, or multiangular defects would be so unlikely to be duplicated elsewhere that fewer characteristics are required for identification. Ultimately, the experience of the analyst will aid in the decision as to what is an acceptable match.

Method and Materials

For this research, an Identicator LE-25 Inkless Foot/Shoe Print Kit was used. This product produces an inked print on a sheet of paper that is 6.5 inches by 12 inches. The ink is a special type that develops only on the paper supplied and not on anything else. This reduces the mess involved with inking or dusting a shoe. The prints on the chemically-sensitized paper appear immediately and require no developing time. The LE-25 Inkless Foot/Shoe Print Kit was very easy to use and involved minimal preparation time to make the print.

Shoeprints were obtained from twenty-six laboratory employees and twenty-eight high school students. Each of the volunteers filled out a short survey consisting of the following questions: name, shoe type, shoe size, how often the shoes are worn, and the age of the shoes. The shoe type and size were recorded because the authors keep and maintain a rudimentary shoeprint database. Whenever a shoe is printed (whether in a case, training, or in research) the authors retain a copy of the print in a filing system that is separated by brand. Although no shoeprint database can ever be complete (because of the infinite number of shoeprint patterns), this is an attempt at creating some sort of system with which to use in case work. The rest of the information listed in the questionnaire was collected in the hopes that trends might be discovered in the final results of this research.

After a period of two months, shoeprints were again obtained from these same volunteers wearing the same shoes. The two sets of prints were then examined by three separate analysts utilizing the overlay method with backlighting. Four criteria were noted by the analysts for each set of shoeprints: individual characteristics that were present in the first print taken that no longer remained on the second, individual characteristics that were not present on the first print but appeared on the second, individual characteristics that were present on the first print and still remained on the second print, and wear patterns observed. All three examiners had to agree before recording the results (Table 1).

Results

Out of the fifty-four sets of shoeprints observed, twenty-two pairs could be positively identified as having a common origin. The remaining thirty-two shoeprints could not be positively identified to a particular shoe based on the experience of the analysts. Some individual characteristics from the first prints were worn away during the two-month period or they were covered up by new individual characteristics, thus making a positive identification impossible. However, it should be noted that for a large portion of those that could not be positively identified, it was not always necessarily a factor of time that hindered the identification. Some of the shoeprints obtained at the beginning of the experiment simply did not have many individual characteristics present for comparison.

The majority of the shoeprints obtained after a two-month period had one or more new individual characteristics in addition to wear. The wear patterns varied in amount and seemed to depend on usage. For example, a shoe worn “every day”, as indicated by the survey form, showed more wear than a shoe worn “a couple of days a month”. If an individual characteristic mark was present on the first print, it was very likely that it would also be found on the second.

It should be noted that there were some limitations that made comparing the two sets of prints somewhat difficult. This experiment involved comparing shoeprints to shoeprints, not shoeprints to shoes. Without the benefit of having the actual shoe to observe, it was occasionally difficult to determine whether an identifying mark was an individual or class characteristic.

Another limitation occurred because one of the inkless pads was oversaturated with chemicals. This caused a transfer of the excess material to the impression, possibly obscuring fine details. The pads are hand dried with a roller before shipping to the customer, but one of our inkless pads still remained too wet after shipment. If the print was distorted and details of the print were obscured, the prints were eliminated and not considered in the data set. The wetness problem, however, soon resolved itself because the pad was used more and dried out enough to work as advertised. If the analysts were still able to make a comparison, the wet marks were noted. Fortunately, these limitations are not often encountered in casework because the suspect’s shoes are usually submitted with the case and can simply be resampled.

Conclusions

The results of this experiment show that a shoeprint examiner should expect to find some new individual characteristics that are not present on the recovered crime scene print in addition to some wear pattern changes. The examiner could often find that it is still possible to make a positive identification, as was the case in twenty-two out of the fifty-four usable sets of prints in this experiment. It may also be found that the individual characteristics needed for comparison are no longer present and a positive identification cannot be made. In an extreme example such as this, it might aid the police’s investigation of the crime to report that the time lag between the crime scene print and the confiscation of the suspected shoes may be a possible factor in the inability to positively identify the print.

If a shoeprint is recovered from a crime scene and a suspect is not apprehended until two months later, it is likely that the shoe will be similar to its original condition at the time of the crime. This is concluded with some reservation, however, because there are several factors that can inf luence the outcome of a forensic examination. These include how often the shoe was worn between the crime and collection as well as to what surfaces the shoe was subjected. Therefore, a case should be investigated even when two months have elapsed between the collection of the shoeprint from the scene and the collection of the suspect’s shoes.

Table 1

Results compiled by three analysts.
(Wear patterns and similar molds were noted but not reflected in the table.)

Figure 1

The print on the left is the first sample; the print on the right is the second sample.

Characteristics 1, 2, and 8 were found in both samples. Characteristics 3 through 6 were not found
in the first sample, but were noted in the second sample. Characteristic 7 was only found in
the first sample. Marked as 9 and 10 are areas of patterns that were consistent in both samples.

[It should be noted that an incomplete inking of the bottom of the first heel impression was obtained and
nearly missed the wear pattern. It should also be noted that some pooling of ink on the top portion of the heel
pattern (second sample) occurred but this problem was eliminated when the ink pad was allowed to dry out.]

For further information, please contact:

J. Matney Wyatt
Hamilton County Coroner’s Laboratory
3159 Eden Avenue
Cincinnati, OH 45219
(513) 946-8759

Bibliography

1. Bodziak, W. J. Footwear Impression Evidence: Detection, Recovery, and Examination, 2nd ed.; CRC Press: Boca Raton, FL, 2000; pp 307, 335, 347.
   
   
2. Hilderbrand, D. S. Four Basic Components of a Successful Footwear Examination J. For. Ident. 1999, 49 (1), 37-59.