12.4: Documenting and preserving footwear impressions

The impression should be documented in two ways: photography and casting. Footwear impressions are not difficult to document and collect, providing you follow a systematic method. The equipment that you will need to document the impression will include: a camera; a flash that can be operated off the camera (either wireless or slaved); a shutter release cable; a tripod that will allow the camera to be suspended upside-down; a level and an L-scale. Your author uses the standard vinyl reversible macro-photography L-scale (300mm x 150mm), but he also glues a golf-ball marker to the face of the scale to assist the analyst in determining the direction of artificial and natural light. Using the flash to add light between near-oblique and 45 degrees can add contrast and depth to the furrows left by footwear that are molded (such as those left in mud, sand or soft dirt); thereby providing an image that has more definition and detail. However, the analyst may need to know if the detail is an individual characteristic made by the shoe or a shadow caused by the addition of the electronic flash. The shadow cast by the golf ball marker allows the analyst to make this determination.

Figure \(\PageIndex{1}\): The L-scale ruler

Note in figure \(\PageIndex{1}\) that the scale has a small circle embossed on its face. This circle is useful to the analyst in determining if the photograph was taken with the film plane parallel and perpendicular to the object. Any deviation would result in an oblong image. That is also why it is important to use a level to make the final adjustments to your camera prior to taking the photographs.

Figure \(\PageIndex{2}\): DSLR camera supported underneath the tripod

The first step is to set your camera on the tripod with the center column inverted. Many agencies utilize tripods with extended booms or multi-position center columns that project over the image being photographed. These tripods are terrific and extremely useful in the crime scene but beware of balance issues; a slight bump of the tripod might send your camera head-first into your evidence. Note that your author does not put the flash on the camera until it has been properly focused and leveled. Your author uses the flash on an off-camera cord as there is nothing worse than having it fall into the impression while making adjustments to the camera or tripod. Your author also attaches the off-camera shutter release wire before he puts the camera on the tripod; and he generally uses a clamp to hold that device from falling into the impression as well.

Figure \(\PageIndex{3}\): Checking the level

Your author also checks the level of the camera twice: once before he focuses the camera and again following the focusing of the camera and the addition of the flash. Also, make sure the camera is on the same plane as the bottom of the impression.

The step that is often forgotten when teaching this technique is to furrow a trench in an L-shape far enough away from the impression as not to damage it or any physical evidence that might be present, yet close enough that the scale will be captured in the frame.

Figure \(\PageIndex{4}\): Do not forget the trough for the scale.

Figure \(\PageIndex{5}\): The scale

The reason for this trough is to allow the scale to be photographed at the same plane as the impression. This accomplishes two purposes: it ensures that the scale and the impression will both be in focus and it corrects distortions caused by the scale not being on the same plane as the object (parallax error).

Figure \(\PageIndex{6a/b}\): Oblique lighting with the flash

While holding the flash at between oblique and 45-degree angles, take the photographs of the impression, firing the flash between the openings of the legs on each side of the tripod. The flash should be held between 3’ and 5’ from the impression. Once you have accomplished this, take a photograph without the flash, if ambient lighting permits (or if you can make manual adjustments to the camera such as bracketing, adjusting the f-stop, or increasing the film speed).

Figure \(\PageIndex{7a/b}\): One for good measure without the flash.

Once the photographs have been taken, a casting of the impression can made using one of the casting materials commonly available from the forensic supply companies (such as Sirchie’s Shake-N-Cast™, Lynn Peavey’s Copy Cast™, or Arrowhead Forensics’ Arrowstone™, amongst others). The process of casting the impression is simple; just follow the instructions provided with the casting medium, mix the compound to the consistency of pancake batter, gently pour it into the impression and allow it to dry. You may also use an alternate method whereby you pour water into the impression and then sift in the casting compound until it thickens if there are concerns that pouring in the mixture will alter the impression. You may have to use or construct a frame that will hold the compound until it dries. Your author will take subsequent evidentiary photographs of the casting in the laboratory once it is dry enough to package as evidence. The best method of packaging the casting into evidence that your author has found is to place the casting on a piece of cardboard that will fit the dimensions of a box the size of a shoe box. He then uses electrician’s plastic wire ties to firmly affix the casting to the cardboard and then gently lowers it into the box.

Figure \(\PageIndex{8}\): 1930's detectives only had plaster of Paris available to them, which is not used today owing to the short shelf-life of the plaster (it turns to dust after a few decades). Today we use dental stone as a permanent method of casting. – Courtesy of the Federal Bureau of Investigations Archives

Molded impressions, or those that are 3-dimensional, are most common to outdoor crime scenes, as are 2-dimensional bloodstained or dust impressions left on concrete; however, bloodstained footwear or impressions that are the product of a suspect stepping in a liquid or powder and transferring it onto the floor can be found in indoor crime scenes. Bloodstained impressions are documented using the same equipment as the molded impressions, only without using the flash to introduce oblique lighting as the flash may cause a ‘hot spot’ or ‘burned’ area that might obscure the details. Dust impressions may require the application of a forensic white light at an oblique angle to aid in visualization. This application is best done with a forensic light as opposed to a flash. The technique for capturing the image of a dust impression still requires the use of a tripod.

Dark prints left in dust or dried bloodstained footwear impressions can be lifted using casting material. It is important to make a frame around the impression using duct tape and then pour the casting material directly over the impression, making sure that the casting material is of the consistency of pancake batter. Allow the casting to dry thoroughly and use a putty knife to gently pry the duct tape away from surface, lifting the entire casting like a hinge. Remember that the recovered impression will be a mirrored image of the original. Also keep in mind that these castings are extremely thin and fragile. It is best to photograph them as quickly as possible and to firmly mount them in a covered box. The investigator should also consider using blood reagents, such as Coomasie Blue, Amido Black or Leuco-crystal Violet (LCV), to enhance bloodstained foot or footwear impressions prior to the application of the above listed documentation and lifting techniques.

Figure \(\PageIndex{9a/b/c}\): Thin casting a dust print

Footwear impressions deposited on carpeting may also be challenging to the investigator to document and collect and may take some creative solutions through trial and error.

Figure \(\PageIndex{10}\): This impression was deposited on a dark gray carpet in a classroom. The medium appeared to be chalk dust. Using a tripod, your author set the camera at f/13, while bouncing the flash off of a nearby white wall. This provided the best image. Lifting this impression proved equally difficult, with the best result coming from the PathFinder™ electrostatic dust lifter.

This impression was deposited on a dark gray carpet in a classroom. The medium appeared to be chalk dust. Using a tripod, your author set the camera at f/13, while bouncing the flash off of a nearby white wall. This provided the best image. Lifting this impression proved equally difficult, with the best result coming from the PathFinder™ electrostatic dust lifter.

Exemplar footwear impressions should be collected from first responders, medical and fire personnel and the investigative staff on scene. Fortunately, there is no need to collect the shoes or even photograph them as there are several inkless shoe print documentation kits available on the market, such as Lynn Peavey’s Inkless Shoe Print™ kit, which produce quality impressions that can be stored for extended periods of time. It is an easy process that requires the wearer to simply step upon the invisible inking pad and then place their foot on the special paper for the impressions. BioFoam is another great product for collecting exemplar impressions.

Figure \(\PageIndex{11}\): BioFoam

Footwear that is collected at the crime scene should be stored as evidence in a box of a size consistent with the original shoe box in which they were purchased. Never place shoes in an evidence box with the soles facing or touching each other. Your author generally wraps evidence shoes loosely in butcher paper and place them individually into boxes, preferring not to store shoes in paper bags. Socks may be stored in paper bags but be certain to record the foot from which the sock was removed. Your author has seen more than one officer wish they had done just that when being questioned on the stand. Agency protocols should prohibit an officer or crime scene technician from writing anything on the sock, especially if the sock is to be submitted for DNA analysis. If it is necessary to mark the sock for identification in court, your author recommends that the officer complete an evidence tag and then use a piece of clean string to tie the tag to the sock, then fold the sock into butcher paper and place the tag on the outside of the butcher paper wrapper. Then place the butcher-paper wrapped sock into an evidence bag.

Shoe analysis

When a shoe suspected of being worn by the suspect of a crime is processed into evidence for forensic analysis, there are certain steps that must be followed in order to properly preserve the evidence. Your author always analyzes each shoe separately. He photographs the shoe upper and midsole and collects DNA-typing swabs from the interior and inner-sole (this is done in the likely hood the suspect will say someone else was wearing their shoes). He then removes the inner sole and examines it using alternate light source and infra-red to determine if one or more wear (foot) impressions are present. If necessary, your author will conduct several experiments for the presence of blood or gunshot residue on the upper, mid-sole, and outsole. If sufficient dirt is built up on the outsole, your author will carefully collect as much as possible for soil comparison with soil found in the crime scene. Following this, the outsole pattern is carefully documented by photography with a scale for comparative purposes. The shoe is returned to evidence, and the work area is cleaned and sterilized prior to processing the mate to the previously processed shoe.