Although the title may seem contradictory and look like a way to attract attention to this article (and if you’re reading this, it worked!), there’s more to it. Please allow me to explain.
First of all, the correct terminology in the forensic field is footwear outsole impressions. Recovery and examination of footwear impression evidence is an important tool in the forensic investigators’ toolbox and can provide essential evidence in a crime scene investigation. The clearer and more defined an impression is, the higher the chance that specific identifiers, like unique wear patterns, cuts and defects, can be recovered and a specific impression can be tied to a specific boot. A series of impressions can help reconstruct a sequence of events, as well as give an indication of the actions and movement patterns of an individual. Additionally, individual gait specifics may be identified and tied to an individual.
But what if your crime scene is on a substrate that is not conducive to crisp and clear impressions? What if your crime scene is, say, in the middle of a mixed deciduous and coniferous forest?
Mixed forest floors consist of multiple layers of pine needles, leaves, detritus, humus and other debris in several stages of decay. This makes for a very soft, almost cushion-like flooring that absorbs the pressure of contact with a human body part. Also, it will leave no clear impression that will show footwear class information, let alone any specific identifiers. How can we find a usable impression?
If you’re looking for usable outsole impressions, you will have a hard time. This has to do with perception and expectation. If you expect to see a print or (part of) tread marks, you might miss all those small subtle clues that show you someone set a foot on that forest floor. Trackers look for “sign”, which can be defined as “any change from the natural state, inflicted upon the environment by the passage of man, animal or machinery”. There are several characteristics to sign, but the most prominent in this example are what in tracking is called flattening, colour change and disturbance.
Although it probably has been an important part of man’s survival since humans started hunting 2 million years ago and has been an integral part of early religion, tracking and searching for sign is above anything about visual perception and object and pattern recognition. Imagine your brain having file folders with images how objects and shapes and people around you look, a process of constant registration, storing, and learning. In order to create order in the seemingly chaotic world around you, your brain will compare what your eyes see with what is stored in your file folders. When a match is found, you will recognise what you see. “Look, it’s my uncle Bob!”
Understanding this principle helps to understand tracking and how to learn how to see sign in different substrates. By exposing a student tracker to as much sign in different substrates, environmental conditions and age of sign and effectively filling his/her file folders, he/she will be able to learn to see sign in seemingly very difficult terrain.
Back to the pine forest. After being exposed to tracker-based training the forensic investigator may be able to identify the subtle flattening, colour change and general disturbance associated with human impressions. Two kneeling positions identified under and partially on the victim link these specific impressions to the victim. From these sign patterns the investigator is able to identify the entry and exit route of this specific subject. Linking the subtle marks on the ground together into an uninterrupted chain of evidence the investigator is able to retrace the steps of the subject. Stride length, straddle, pressure, dwell time and pitch angle all serve as indicators of the suspects’ actions. Until the investigator hits a “track trap”.
In tracking a track trap is defined as an area conducive to good sign. In this case the subject stepped on an old molehill. The soft, relatively moist sand leaves a very clear impression. As an isolated print this impression would be of limited value, but the investigators’ ability to link the incident to this track through an uninterrupted chain of subtle clues increases the value of this piece of impression evidence, effectively enabling him to link this print to the incident.
If you’re only looking for clear recoverable prints you may miss a potentially large amount of clues and evidence, which may help you reconstruct scenarios, effectively steering your investigation. In some instances these “breadcrumbs” will lead you to a good impression, a secondary crime scene, discarded evidence in an area where the suspect felt safe and dropped his/her “forensic guard”, or maybe even the suspect.
(No humans were hurt during the writing of this article. All pictures were taken during a training scenario.)