Footwear Casting Lesson 2023 PDF

FID 5004 Physical Matching Footwear: Recovery of 2-D and 3-D Impressions  Session Objectives 1. Discuss footwear evidence. 2. Discuss casting materials. 3. Examine the procedure for casting a footwear impression. 4. Discuss how to retrieve 2-Dimensional impressi...

FID 5004 Physical Matching Footwear: Recovery of 2-D and 3-D Impressions  Session Objectives 1. Discuss footwear evidence. 2. Discuss casting materials. 3. Examine the procedure for casting a footwear impression. 4. Discuss how to retrieve 2-Dimensional impressions.  Crime Scene Footwear The discovery of footprints at crime scenes has been noted for hundreds of years. The difference is that we now have trained experts in footwear. Outsole - referring to the outer sole surface of footwear.  May or may not identify an accused.  Will provide an investigative lead.  Total recovered outsoles at crime scenes represent as little as 1% of the general footwear population.  Crime Scene Footwear Footwear impressions will assist in determining the route of travel through a crime scene including,  Point of entry.  Where they walked.  Point of exit.  Whether one or more persons were at the crime scene. Can corroborate a witness or suspect's statement.  Crime Scene Footwear Footwear is often overlooked. There is often an equal or greater chance of finding footwear rather than fingerprints. Criminals,  often wear gloves, leaving no prints (a by-product of people watching CSI).  possibly walking around a scene, but not touching anything.  will always have to walk through a crime scene, contacting surfaces (Locard’s Principal).  Types of Impressions There are three types of Crime Scene Impressions  Visible - Seen by the naked eye  Latent - Requires a development medium  Plastic - 3 Dimensional  Types of Footwear Evidence 2-Dimensional Transfer Impression,  Most common, a result of transfer of material picked up by the footwear or foot and redeposited.  Are positive impressions and represent what the outsole of footwear or foot, looks like. Negative Impression,  Raised portion of outsole picks up material from the substrate.  Leaves a reverse image of the outsole, i.e., stepping on a dusty surface.  Types of Footwear Evidence Dry Origin Impression,  Usually made with exterior dry soil residue.  Dry material transferred to a dry surface.  Residue and surface do not bond well, which makes this type of impression fragile. Types of Footwear Evidence Wet Origin Impressions,  Outsole contacts something wet or moist then contacts dry substrate.  Greater bonding to surface and may be absorbed into substrate.  Impressions vary with substance or colour leaving visible impressions.  Others may be transparent requiring further development. Types of Footwear Evidence Three Dimensional,  When outsole permanently deforms substrate, i.e., soil, mud, and snow.  Usually, shallow indentations in substrate but can be deep depending on substrate.  Does pick up additional detail of the outsole not produced by 2-D impressions i.e., sides of the sole or depth of characteristics.  Types of Footwear Evidence The reproduction of footwear is a simple process. With multiple impressions there can be variances in appearance. Completeness and quality of impression can be impacted.  Depending on motion, speed and force applied.  Affects include biometrics of person, external forces, and the type of substrate.  Is it pliable or flexible, wet, dry, porous, or non-porous.  The make-up of the substrate i.e., sand, snow, or mud.  Other influences that effect the impression i.e., stones, branches, debris, uneven or textured surfaces, sticky or wet.  Recovery of Impressions We do not have control of how or where an impression is deposited. We do have control of how to recover those impressions. General Rule - recovering the original item which contains the impression should always be made if it doesn’t destroy the impression.  Paper, glass, cardboard should always be seized.  If it is a serious crime, you may have to remove wood flooring or tiles.  Always photograph scene and impressions (close-up with scale, at 90°).  Always use identifiers - numbers or letters (F1, F2,...).  Make notes as to the location of impressions and directionality if possible.  Enhance 2-D and cast 3-D impressions.  Scene Search Always start with a walk-through or cursory search.  Use high-intensity oblique lighting.  Use a flashlight.  Alternate light sources. Use stepping plates or booties to prevent further impressions. Methodical search of a small area or one room at a time using a light source.  If possible, darken the room and place light at a very low angle to graze the ground (oblique lighting). May require the use of electrostatic lifters, which pick up dry impressions that may not be seen.  Photography of Footwear Scene and Examination quality.  Use the largest resolution available.  RAW images are always the best. They capture original unprocessed data, like a film negative.  Focal length roughly matching the human eye, approximately 50mm.  May have to adjust the height of the camera to properly frame shot.  Always use a scale in photograph, for later enlargement to actual size.  Photography of Footwear  Scale should be placed along the side of the impression.  If 3-D, the scale should always be placed at the bottom of the impression. An L-Shaped ruler is used to determine if the image is at 90°.  Circles on the scale are for perspective correction.  If the image is not at 90°, then the circles in the scale will appear elliptical and not round. Photography of 3-D Impressions  Focus on the bottom.  The scale must be on the same plane, as the bottom of the impression.  Scales at different heights, can affect the enlargement. Examination Quality Photography The camera. Use a professional DSLR camera set at its highest resolution. Choose aperture priority with the appropriate f-stop. Select RAW or the combined RAW/JPEG setting. Select a low ISO setting and manual focus. Use the camera’s timer along with the wireless remote flash capabilities and remote flash as necessary for your camera to provide off-camera oblique lighting. F1 Prepare Impression. Place an L-shaped or long straight flat ruler alongside the length of the impression. If it is a 3-dimensional impression, carefully position the ruler on the same plane (level) as the bottom of the impression. llel Include a label on the ruler to link this impression to the identifier number Para used in the general crime scene photographs and notes, as well as in the subsequent casts or lifts. Position the camera. Attach the camera to the tripod and position it directly 90° above the impression. Make sure the sensor (focal plane) of the camera is parallel to the impression being photographed. Use the Live View Mode or viewfinder to assure the impression and ruler fill the image frame.  Why Cast?  Lifelike or actual size of impression, including uneven surfaces.  Reproduces microscopic characteristics.  With deep impressions, a cast reproduces details of the side of the shoe which usually is not reproduced in images.  Provides tangible 3-dimensional evidence.  Confirms your images.  Casting Footwear Whenever there is a 3-D impression it should be cast.  Captures positive representation of the shoe.  The more details in the impression the more valuable the evidence. Properly casted impressions are more valuable to an examiner than photography. There are limitations on photography. When enlarged to natural size i.e., loss of sharpness and resolution. With Casting - there is no focus problem and gives the examiner a 3-D aspect. With poor impressions such as those made in stone or debris, casting may be more accurate than photography.  Casting Footwear Prior to 1970 the casting material of choice was Plaster of Paris (used for decades). A disadvantage of Plaster of Paris was it is a soft form of gypsum (to clean the cast with water and soft brush destroyed much of the detail). In early 1970, dental stone became popular as a casting material and in 1986, FBI Law Enforcement Bulletin recommended that only dental stone be used for casting. Dental Stone vs. Plaster of Paris  Dental stone is stronger and more durable.  Easy to use.  Easy to acquire.  Dental Stone Used by dentists to produce an accurate and detailed impression of teeth.  Is a form of plaster.  Calcium sulfate dehydrate is a natural material which is mined.  Calcination - heating process to dehydrate gypsum to become calcium sulphate hemihydrate (the hardened version). Dental stone is mixed with a pre-determined amount of water.  Can be mixed in a container or in a Zip lock bag.  The viscosity (thickness of the fluid mixture) cannot be too watery or too thick.  Consistency should be thin pancake batter or thick cream.  The Pour Set the mould form.  Use metal form.  Cardboard.  Or build up surrounding soil. The mould prevents casting material from spreading over a wide area. A thin mold is fragile and may require more casting material.  Ensure the mold form is slightly larger than the impression.  Approximately 2lbs of dental stone to 8 oz of water.  Mix for 3 minutes before pouring, to ensure the mixture will pour evenly and make a stronger cast.  The Pour Start pouring just outside of the impression but direct the flow into the impression. Move along the impression while mixture is pouring. Pour behind the leading edge to push the mixture into the impression. Once poured the casting should be left to harden. Place a label into the casting with Identifiers, date, location, and Initials. You can also wait until it starts to harden then scratch info into the casting material.  Cast can be removed from the ground in about 15 to 20 minutes (depending on the outside temperature).  Should allow 24-48 hours before removing any soil or debris.  Can be cleaned with water and a soft brush.  Casting Impressions in Snow Snow is constantly changing, it is categorized as,  Fresh, refrozen, wet, dry, slushy, compact loose, and granular. Recovery requires immediate attention and is affected by,  Blowing snow.  Additional snowfall.  Melting due to temperature change.  Disturbance. Marking location of footwear must be a priority! Risk of,  Weather instability.  Low contrast which makes it easily overlooked and trampled on.  Photographing Snow Prints  Same procedure as any other 3-D impression  Scale placement, identifiers, blocking ambient light, using oblique lighting.  Difference is the contrast of snow prints. Bright white will cause meter to underexpose, and the image will not be useful.  May require adjusting the contrast level and overexposing by 1 or 2 stops.  Try opening your aperture i.e., f22 to f16.  Photographing Snow Prints Another way to improve contrast is to use coloured sprays. Products like Snow Print Wax or Krylon Grey Primer. Paint aerosols may cause snow to melt due to the chemicals in the paint. Caution should be used,  In powdery snow, the spray force may damage the impression.  Initially spray at a very low angle and about 1½ feet away, then move closer to evenly cover the entire impression. The purpose of highlighting,  To increase contrast to the higher portions of the impression.  Spraying may decrease your working time with the impression.  The amount of spray is a judgement call. Photograph immediately! Cast immediately or cover with a box, until ready to cast.  Casting Impressions in Snow Other Options Snow Print Powder  Red powder used with a fingerprint brush on wet, melting, or slushy impressions.  Provides high contrast, then followed by casting. Snow Print Plaster (Snow Stone) - Powder  Introduced in 2014 has a quick and easy application.  Can be used with or without highlighting with Krylon.  Works in all temperatures.  First sift a small amount over the impression to cover the bottom of impression.  Then remainder mixed with water. At first watery and then it thickens when it is ready to pour over the impression.  Can be removed in about 10 minutes, and completely dries in 24 hours. Casting Impressions in Snow Snow Print Wax  Developed in 1982 in Sweden.  Aerosol spray, bright red in colour.  When applied to impression it produces a wax shell.  Casting done using dental stone. Dental stone fills in the wax and once it sets, the wax is lifted with the dental stone. Dry Casting with Dental Stone  Layer impression by sifting three layers of dry dental stone over the impression.  Then preparing a regular mix of dental stone.  Works best with moist snow - relies on the moisture to absorb the first layer of dental stone. Casting Impressions in Snow Yellow Sulfur  Used for many years - more time consuming.  It can produce excellent detail of snow impressions.  This can be challenging to those who rarely use it.  Requires melting yellow sulfur in a pot over an electric heating element or hot plate.  Required continuous stirring during the melting process.  Let it cool down to just before it solidifies, and then pour onto the impression. Casting Impressions in Snow Sulfur Cement  Introduced in 2007.  Less flammable than sulfur.  Requires the same method as sulfur.  More useful for larger impressions like tires.  Casting Impressions in Snow Key Points 1. The amount of detail varies considerably in different types and conditions of snow. 2. Impressions in snow should always be photographed first. 3. Highlighting impressions is an excellent method to enable better contrast recovered through photography. In colder climates, coating the impression is possible. 4. Casts of snow impressions provide additional detail to supplement photography of snow impressions alone.  Break 5 Minute Break  Gait Measurements Gait - manner of walking or moving on foot. Gait Analysis - the study of human walking. Forensic gait analysis is a relatively new term, which is divided into two parts,  Analyzing how a person walks through a crime scene. Can be done by viewing them on surveillance cameras.  There could be other things identifying how a person walks.  Limping, posture, limb movement.  Measuring the distance between footwear/foot impressions.  Gait Measurements Gait Measurements Include, Stride Length - Linear distance between two steps of the same foot. Step Length - Linear distance a foot moves in front of the opposite foot. Stride width/walking base - Transverse distance between left and right foot measured perpendicular to direction of travel.  Measured at mid-point of the heel. Foot Angle/Toe-in or Toe-out - Angular measurement of midline of foot in relation to direction travelled. These are general measurements and not unique to one individual, it can provide information about a person as an investigative lead, or to eliminate.  2-D Footwear Impressions When a substance is acquired on footwear outsoles and transfers back to a substrate, replicating the outsole in the form of a 2-dimensional impression. Includes both visible and latent impressions. Substances like, dust, dirt, mud, blood, etc. Substrates include, wood, tile, carpet, asphalt, and concrete, etc. Can also include, counters, doors, paper, broken glass, cloth, and skin.  2-D Footwear Impressions General Protocol for Detection of 2-Dimensional Impressions 1. Search with specialized light sources and electrostatic lifting. 2. General crime scene photography. 3. High resolution photography. 4. Recovery of original evidence, when possible. 5. Use other lifting and enhancement techniques (i.e., Gelatin lifter). Using enhancement techniques increases the chance to recover additional details not located with general photography alone (i.e., Image Subtraction). Lifts provide 1 to 1 size recovery without the scale, focus, or perspective problems associated with photography.  2-D Footwear Impressions Positive or Transfer Impressions Two-dimensional impressions that occur when materials acquired on the raised outsole tread are transferred to the substrate. Negative Impressions Negative impressions are when the raised outsole tread removes material from a substrate and produces what is known as a negative impression.  2-D Footwear Impressions Dry Origin Impression Both the shoe and the receiving substrate are dry at the time the impression is made. Occurs when dry footwear or foot, track across a dirty substrate and then onto a dry, but relatively cleaner substrate. Dry origin impressions are easily lifted from nonporous and from many porous substrates. Typically, very thin and composed of light-coloured dust or residue making them either barely visible or latent. Can easily be wiped away and destroyed.  Wet Origin Impression Occurs when the shoe outsole and/or the receiving substrate are damp or wet. When moisture is present, the impression will have a greater bond to the substrate and often includes some penetration into or absorption by the substrate. Before lifting impression consider,  Porosity of the substrate - porous or non-porous.  Substrate condition - clean or dirty.  What is the transferred material.  Clarity of impression - thin or barely visible.  Sequence of lifting or enhancement - which should be done first. Not every impression can be lifted with any one method because they are not all composed of the same materials or the same substrate.  Static Electric Method One way to remove an impression from a dusty substrate, or a thin dry impression, is to use a static charge. A polyester film, with one side coated with a black glossy surface for high contrast and the other side coated with aluminium, for distribution of the static charge. Static electric lifters do not interfere with the use of chemical enhancements. Should be considered prior to any other enhancement (i.e., impression is partially in dust and partially in another substance such as blood).  Gel Lifters Water based gelatin materials on a linen-reinforced natural rubber backing. Has dyes, anti-fungal agents, and other materials. Low tact with minimal stickiness, allowing it to lift impressions from almost any surface. Comes in various sizes in black, white, and transparent.  Gel Lifters Lifters have a clear acrylic sheet on the tacky side to protect the gelatin. Lifters may degrade over time; the amount can be affected by:  Material being lifted.  The substrate.  If the cover sheet is reapplied.  Stored in a warm climate - before/after.  Best stored in a covered plastic container, without cover sheet and then scanned/photographed.  Chemical enhancement.  Adhesive Lifters Are the same adhesive tape used for fingerprints.  Rolls come in 4” size.  Come with either a black or white backing card for contrast.  Mikrosil© Casting material used for tool marks and other impressions.  2 step mixing process.  Depending on the size if impression.  Good for partial impressions.  Picks up texture of substrate. Key Points - Lifting 2-D Impressions 1. 2-dimensional impressions are composed of varied substances on varied substrates and therefore require a variety of lifting materials and methods. No single method of lifting will work on all impressions. 2. Lifting or other forms of enhancement should be attempted whenever possible to supplement photography, as they provide additional details of the impression. 3. Electrostatic lifting, if unsuccessful, will not destroy impressions or prevent subsequent methods of lifting or enhancement from being attempted. 4. Electrostatic lifting is routinely used at a crime scene to search large areas where no visible impressions are present, but where the circumstances exist for the likely presence of latent dust impressions. 5. Black and white gelatin lifters are more versatile and have more lifting power because of their tacky surface. They can be used in a variety of applications to lift original impressions, powdered impressions, and impressions that have been treated chemically. 6. Adhesive lifters, in particular makeshift adhesive lifters, do not provide the best method of lifting impressions. 7. The use of Mikrosil© is an excellent method for making a complete lift of powdered impressions. Enhancement of Footwear Impressions 1. Enhancement is a way to increase the visualization of impression evidence. The improved visualization not only increases the number of impressions detected at a crime scene but also improves the detail available for examination. 2. Enhancement can be achieved through, a) Forensic Photographic Techniques  High contrast photography (black and white) and use of filters (red/green).  Oblique lighting.  Cross polarization - use of polarizing filter on light source and camera.  Ultraviolet photography - using long wave bands of 400nm and below.  Infrared photography - using short wave bands of 700nms and above. b) Through Physical Methods Such as Lifting Techniques  Fingerprint powders.  Gelatin lifters.  Electro-static lifters. Enhancement of Footwear Impressions c) Through Chemical Reagents Many of the treatments used in recovery of fingerprints can be used to enhance 2-D footwear,  Cyanoacrylate (C.A./Glue fuming).  Ninhydrin.  Physical developer.  Through digital software - Adobe Photoshop (image subtraction). 3. Several chemical reagents are highly successful for the detection and enhancement of bloody footwear impressions, many of which can be used in sequence. 4. Efforts to recover and enhance impression evidence should always be sequenced to use non-destructive methods first, then other methods to maximize the chances of recovering additional detail. Taking Test Impressions for Comparison In most cases 2-D comparison impressions are enough.  A 2-D impression on a transparency is helpful for impressions on a tile floor. Photographs of 3-D impressions or a cast impression.  Overlaying transparency helps with size, wear and looking for accidental characteristics. Methods 1. Ink and paper - using printer’s ink (used in fingerprinting) dries quickly and provides great contrast. 2. Magnetic fingerprint powder on paper. Requires coating the outsole with a thin layer of an oily substance like WD40 or cooking spray. 3. An inkless shoe impression kit uses a chemical solution. When pressed against chemically treated paper, an impression is produced. Taking Test Impressions for Comparison Pictured is an inkless shoe impression kit, which uses a chemical solution on a pad (yellow area). The footwear or foot is coated with the chemical from the pad and then placed on the special chemically treated paper, which then produces an impression. Best results are obtained if the footwear is worn, which allows for even pressure.  References Bodziak, W. J. (2017), Forensic Footwear Evidence. CRC Press Taylor & Francis Group. "footprint in the snow" by Tim Evanson is licensed under CC BY-SA 2.0 https://search.creativecommons.org/photos/136ead60-c81c-4319-9500- 559eb7e86124 Crime Scene Investigators Network. https://www.crime-scene- investigator.net/footwear-and-tire-track-photography.html Alternate Force Network https://www.alternateforce.net/snowprinwax6.html How It’s Done https://www.forensicsciencesimplified.org/fwtt/how.html  References Shoe and Tire Impressions in Snow: Photography and Casting, Lesley Hammer, James Wolfe State of Alaska Department of Public Safety Scientific Crime Detection Laboratory Anchorage, AK http://www.ronsmithandassociates.com/pdf/Instructor_Publications/lhammer/Ha mmer-Lesley-Wolfe-James-Shoe-and-Tire-Impressions-in-Snow-JFI-53-6-2003- p-647-655.pdf Footwear, The Missed Evidence http://www.crime-scene-investigator.net/footwear.html Bureau of Criminal Apprehension, A division of the Minnesota Department of Public Safety https://dps.mn.gov/divisions/bca/bca-divisions/forensic- science/Pages/forensic-programs-crime-scene-edpl.aspx  The End Questions?