IAI Footwear cheat sheet

Tread evidence falls into three classes: impressions (3D, in soft media such as soil, snow, mud), imprints (2D, on hard surfaces via residue, dust, blood, or compression), and transfers (2D deposited on a surface by a shoe or tire).

Individual characteristics needed for identification include tread wear patterns, cuts, nicks, tears, punctures, embedded foreign objects (stones, glass), and manufacturing defects; class characteristics (pattern, size, pitch) only narrow the candidate pool.

Tread pattern geometry is described by pitch (distance between repeating design elements), groove width, sipe placement, and the lug or rib arrangement; measure pitch center-to-center over several repeats and average to reduce measurement error.

Tire coding: the DOT plant/date code is the final four digits of the DOT serial, where the first two digits are the week and the last two the year of manufacture (e.g., 2319 = week 23 of 2019); the full TIN is 10-13 characters depending on tire type.

Tire size format P225/60R16 97H: P = passenger, 225 = section width in mm, 60 = aspect ratio (sidewall height as percent of width), R = radial construction, 16 = rim diameter in inches, 97 = load index, H = speed rating.

Shoe sizing: US, UK, and EU (Paris point) systems are not interchangeable; EU size = (last length in cm) x 1.5 approximately, so convert and document the system used rather than reporting a bare number.

Photograph footwear and tire evidence with a scale in the same plane as the impression, fill the frame, use oblique lighting to reveal tread detail, and include an overall, a mid-range, and a close-up with scale; cast 3D impressions before lifting 2D ones.

Collection methods: dental stone for soil/snow casts, electrostatic dust print lifter for dry residue on hard surfaces, gelatin or lifting tape for blood and wet residue, and swabbing for DNA before any chemical enhancement.

Comparison workflow: known exemplars are taken from the suspect's actual shoes or tires (not catalog images), test impressions are made in the same medium as the questioned impression when possible, and the examination proceeds class characteristics, then wear, then individual defects.

A conclusive identification requires agreement of class characteristics plus sufficient individual characteristics; exclusion requires a demonstrable disagreement in class or individual features, and an inconclusive result is reported when the evidence is insufficient or distorted.

Tread wear is asymmetric: toe/heel drag, outer-edge wear from camber, and brake/acceleration wear on drive tires create patterns that can link a shoe or tire to a track and indicate which foot or wheel position produced it.

Track dynamics: stride length (heel-to-heel of successive same-foot impressions), step length (heel-to-heel of alternating feet), and walking base (midline to midline) are measured in cm; stride is roughly twice step length in normal gait.

Direction of travel in soil impressions is inferred from greater depth and soil throw at the toe (forward push-off) and from the heel's cleaner, sharper rear edge; in tire tracks, look for the compression wave ahead of the tire and ejection behind it.

Photogrammetry and 3D scanning (structured light, laser) produce measurable models of impressions; report measurement uncertainty and never state a dimensional match finer than the resolution of the capture method.

Databases: footwear outsole databases (e.g., commercial and manufacturer pattern collections) aid pattern identification but an unknown pattern match is an investigative lead, not an identification.

Report language: state the basis of the conclusion (features compared, number and quality of individual characteristics), the limitations (distortion, partial impression, medium), and avoid statistical probability claims not supported by validated data.

Chemical enhancement sequence for latent footwear impressions on porous surfaces: document and photograph first, then physical developer or silver nitrate for paper/cardboard, and ninhydrin or DFO for amino-acid residues; order matters because reagents can destroy later tests.

On non-porous surfaces, use powder (conventional or magnetic) or cyanoacrylate fuming before dye staining with a laser or forensic light source; blood impressions can be enhanced with leucocrystal violet, amido black, or luminol (luminol is destructive to DNA, so swab first).

Electrostatic dust print lifting works on dry, dusty impressions on hard surfaces and does not work on wet or greasy residues; the lifted film must be photographed with scale and stored flat.

Casting 3D impressions: mix dental stone to a smooth consistency, pour from one edge to avoid trapping air, reinforce with gauze or a plaster backing, and allow full set before lifting; label with orientation, case number, date, and location.

Snow impressions are cast with snow-print wax or a dental stone/snow mixture chilled before pouring; photograph with a contrast medium (e.g., sprayed snow wax) before casting.

Soil and debris from a cast or impression can be analyzed for pollen, minerals, and particle size to link a shoe to a location; collect reference soil samples from the scene for comparison.

Chain of custody for impressions: record the exact location, orientation, medium, lighting, weather, and any disturbance; each cast or lift gets a unique item number and is packaged to prevent abrasion.

Shoe and tire exemplars should be collected with the item itself when possible; if only photographs are available, document why and treat comparison as limited, since wear and defects may not be captured.

Tire track evidence includes the track width (distance between the centers of the two tires on an axle), the wheelbase (distance between front and rear axles), and the turning radius; these measurements can identify vehicle class.

Dual rear tires on trucks produce paired tracks; the gap and offset between them, plus the difference in track width between front and rear axles, help distinguish light trucks, heavy trucks, and passenger vehicles.

Tire tread depth affects the impression: worn tires show shallower grooves and fewer sipes; measure tread depth on exemplar tires and compare with groove depth in the impression, accounting for soil compression.

Tire defects that act as individual characteristics: cuts, gouges, embedded objects, retread seams, uneven wear from misalignment, and manufacturing anomalies such as a missing or malformed lug.

Tire rotation and position: a track may show which tire was on which axle and side through wear asymmetry and the direction of the tread pattern; note that directional tires have a defined rotation direction.

Accelerating and braking produce characteristic tire marks: acceleration slip marks are darker and shorter, braking skid marks are longer with a leading edge that darkens toward the end of the skid; ABS braking can leave intermittent dash marks.

Tire impressions in soil should be measured for pitch and groove width at several points along the track to detect distortion from turning, acceleration, or soft ground; distortion must be accounted for before comparison.

Vehicle identification from tire tracks alone is class-level; a specific vehicle identification requires individual tire characteristics plus corroborating evidence (wheelbase, track width, and tire exemplars from the vehicle).

Footwear impression evidence can establish presence at a scene, number of persons, movement path, and association between a shoe and a suspect; it cannot by itself establish when or by whom the shoe was worn.

Shoe sharing and theft limit the strength of a footwear-to-person link; report the association as shoe-to-impression, not person-to-impression, unless other evidence supports the link.

Size estimation from an impression must account for the outsole being larger than the foot, shoe type, and impression distortion; report a range, not a single size.

Test impressions should be made with the actual shoe in a medium matching the questioned impression (soil, dust, blood) and at comparable depth; catalog or stock photos are inadequate for individual comparison.

When a suspect's shoes are seized, document condition (wear, cleanliness, foreign material), photograph all outsoles, and collect any soil or debris for comparison before test impressions.

Quality assurance: use a second examiner for verification in identification cases, document all examination steps, and retain original photographs and casts; proficiency testing and validated methods support admissibility.

A footwear pattern match to a database is an investigative lead only; an identification requires comparison to the actual shoe and agreement of individual characteristics.

Common error sources: distortion from the medium, partial impressions, overlapping tracks, cleaning of the shoe, and wear between the crime and the seizure; each must be addressed in the report's limitations.

Footwear impression recovery on fabric and upholstery: use a vacuum or lifting techniques suited to the surface, and consider gel lifters for blood impressions on fabric; document before any treatment.

Photography of tire tracks should include the full track width, a scale across the track, and a sequence of overlapping frames along the track; record the vehicle's direction of travel and the track's position relative to fixed scene features.

Measurement tools: calipers for groove and pitch measurements on casts and exemplars, a tape or laser measure for track width and wheelbase, and a digital level for slope; record units (mm, cm, inches) explicitly.

Tire sidewall markings to record: size, load index, speed rating, DOT code, M+S or 3PMSF marking, and the tire model name; these support class-level comparison and manufacturing date estimation.

Footwear markings to record: brand, model, size, country of manufacture, and any visible wear or damage; the outsole pattern is compared, not the upper.

Statistical support for impression evidence is limited; do not present random-match probabilities unless derived from a validated, population-specific study, and state the basis of any frequency claim.

Report structure: item description, examination method, results (class, wear, individual features), conclusion with a defined scale (identification, inconclusive, exclusion), and limitations.

Court presentation: explain class versus individual characteristics in plain language, show the questioned and known impressions side by side with scale, and be prepared to explain distortion and its effect on the comparison.

A partial impression can still support identification if it contains sufficient individual characteristics; conversely, a full impression lacking individual detail may only support class association.

Overlay and superimposition techniques (digital image comparison, transparent overlays, and feature-mapping software) aid comparison but must preserve original images and document any enhancement applied.

Ridge and groove detail in footwear outsoles includes sipes (thin slits), lugs, and tread bars; sipes are common to a model (class) unless damaged or malformed (individual).

Footwear impression age cannot be reliably determined from appearance alone; soil moisture, weather, and disturbance affect degradation, so report age only as an estimate with stated assumptions.

Tire track width measurement: measure from the center of the left tire track to the center of the right tire track on the same axle; repeat at several points and average to reduce distortion error.

Wheelbase from tracks: locate the front and rear axle tracks by the change in tread pattern and the presence of turning or scrub marks; measure along the direction of travel between axle centers.

When tracks cross, the track on top was made later; document the crossing and the relative depth and soil displacement to establish sequence.

Evidence packaging: casts are packaged in rigid containers with cushioning, lifts are stored flat in protective sleeves, and shoes are air-dried if wet and packaged separately to prevent cross-contamination.

Footwear impression comparison scale: identification (the impression was made by the shoe), high degree of association, inconclusive, and exclusion; each conclusion must be supported by stated features.

The ACE-V framework (Analysis, Comparison, Evaluation, Verification) applies to impression evidence; document each stage and have a second examiner verify identifications.

Tire track examination can distinguish tire type (passenger, light truck, heavy truck, off-road, winter) by tread design, sipe density, and lug depth; this supports vehicle class narrowing.

Shoe outsole manufacturing: molds produce repeating patterns with mold-flow lines and sprue marks; these manufacturing artifacts are class or sub-class characteristics, while damage after manufacture is individual.

Impression depth in soil depends on load, soil moisture, and bearing capacity; a deeper impression does not by itself indicate a heavier person or vehicle without accounting for the medium.

Known exemplars from tires: record the tire position on the vehicle, the tire's DOT code, tread depth at multiple points, and any damage; test impressions in soil or on paper with ink or dust as appropriate.

Documentation of footwear evidence includes a sketch of the scene with impression locations, orientation, and relationship to other evidence, plus a photo log with frame numbers and scale references.

Limitations to state: medium distortion, partial or overlapping impressions, cleaning or wear of the exemplar, and the inability to determine wearer identity from the impression alone.

Shoe outsole materials (rubber, EVA, polyurethane, leather) affect impression quality: softer materials conform to the medium and produce more detail, while hard materials produce sharper but shallower impressions.

Tire tread patterns: symmetric, asymmetric, and directional; asymmetric tires have distinct inner and outer edges, so the track reveals which side of the vehicle faced outward.

Siping and lug design affect traction and leave characteristic thin lines in impressions; count sipes per lug and compare their spacing as class characteristics.

Footwear impression enhancement on dark surfaces: use oblique lighting, reflected ultraviolet, or a forensic light source; on light surfaces, use oblique lighting and powder to increase contrast.

Cast and exemplar comparison should use the same measurement reference (e.g., pitch center-to-center) and the same units; convert and state the conversion if the original measurements used different units.

Tire track evidence at a scene should be protected from traffic and weather; cover impressions with shelters, photograph before casting, and record weather conditions at the time of recovery.

When a vehicle is available, test impressions of its tires in the same medium and at comparable load are the strongest comparison; catalog or manufacturer images are insufficient for individual comparison.

Report the number of individual characteristics observed and their quality; a conclusion of identification should rest on multiple, independent, well-defined features rather than a single defect.

Footwear impression evidence can be used to link multiple scenes to one shoe; a series of impressions with the same individual defects supports a common source across scenes.

Tire track width and wheelbase data can exclude vehicle classes; a track width that does not match a suspect vehicle's specification excludes that vehicle at the class level.

Measurement of a shoe impression length should be taken from the heel to the toe along the long axis, with the impression's distortion noted; compare with the shoe's outsole length, not the foot length.

Bloody footwear impressions can be enhanced and also sampled for DNA; swab the impression before chemical enhancement and document the sampling location.

Footwear impression evidence on a victim or clothing should be photographed in place and lifted with appropriate techniques; the location on the body supports reconstruction of the event.

Tire marks on a roadway (skid marks) are measured for length and curvature to estimate speed; the formula uses drag factor and braking distance, and the result is an estimate with stated assumptions.

Common footwear pattern features: heel and toe separate pieces, tread bars, logo placement, and size markings molded into the outsole; these aid pattern identification but are class characteristics.

Evidence retention: keep casts, lifts, photographs, and exemplars for the case duration; document any transfer of evidence and maintain chain of custody records.

Footwear impression comparison requires the questioned and known impressions to be oriented consistently; rotate digital images to a common reference and document the rotation applied.

Tire track examination should record the track's position relative to the road edge, lane markings, and other tracks; this supports reconstruction of vehicle path and lane position.

Dual tire tracks from heavy vehicles show a characteristic gap between the two tires on the same side; measure the gap and compare with the vehicle's dual spacing specification.

Tire tread depth gauges measure in millimeters or 32nds of an inch; record the unit and convert consistently when comparing with impression groove depth.

Footwear and tire evidence should be collected before other evidence processing when it is fragile or weather-exposed; coordinate with the evidence team to avoid destruction.

Impression evidence in snow should be photographed with a contrast medium and cast promptly; melting and refreezing distort detail, so record temperature and time of recovery.

Report writing should avoid absolute certainty language when the evidence is limited; use a defined conclusion scale and explain the basis for the chosen level.

Peer review and technical review of impression reports reduce error; document the reviewer, date, and any changes made to the conclusion.

Footwear impression evidence can support a timeline only through contextual evidence (e.g., a fresh impression in mud after rain); the impression itself does not carry a timestamp.

Tire track evidence can indicate the number of vehicles at a scene by the number of distinct track pairs and their overlap; document each track pair separately.

Shoe outsole wear patterns can indicate the wearer's gait and foot dominance; the outer heel wear on the dominant side and toe wear from push-off are common, but interpretation is probabilistic.

Tire wear patterns from misalignment (feathering, cupping, one-sided wear) can be individual characteristics if the wear is distinctive; document the wear pattern on the exemplar tire.

Impression casting materials should be mixed per manufacturer instructions; incorrect water ratio weakens the cast and can lose fine detail.

Footwear and tire evidence should be photographed with a color reference and scale; color reference aids in documenting blood or other residues.

Comparison documentation should include a feature map or annotated images showing each matched feature; this supports the conclusion and aids court presentation.

When the evidence is insufficient for identification, report inconclusive rather than exclusion unless a class or individual disagreement is demonstrated.

Footwear impression recovery from a vehicle: check pedals, floor mats, and seats for impressions; use appropriate lifting techniques for each surface and document the location.

Tire track evidence from a vehicle can include tire impressions in mud on the vehicle's own tires; compare with the scene tracks to link the vehicle to the scene.

Measurement uncertainty should be reported for dimensional comparisons; state the resolution of the measuring tool and the repeatability of the measurement.

Footwear impression evidence can be used to estimate the number of steps and the direction of travel; stride and step length measurements support this reconstruction.

Tire track width can be affected by tire pressure, load, and turning; record these factors when measuring and account for them in comparison.

Impression evidence should be collected with control samples from the medium (soil, dust) to support interpretation of the impression's formation.

Footwear and tire evidence reports should be written for a lay reader; define technical terms such as pitch, sipe, and class characteristic.

Quality assurance for impression evidence includes validated methods, trained examiners, proficiency testing, and documented technical review.

Footwear impression evidence can be used in a series to link scenes; the same individual defects appearing in impressions from different scenes support a common source.

Tire track examination should record the track's direction of travel and the vehicle's likely path; this supports reconstruction of the event.

Impression evidence should be photographed before any enhancement or casting; the original state must be documented.

Footwear and tire evidence should be collected with appropriate tools and packaged to prevent damage; casts and lifts require rigid or flat packaging.

Report conclusions should be based on the examination of the actual exemplar, not on photographs or catalog images, unless the limitation is stated.

Footwear impression evidence can be used to support or refute a suspect's account of movement; the location and orientation of impressions are relevant.

Tire track evidence can be used to identify the vehicle class and, with individual tire characteristics, a specific vehicle.

Documentation of impression evidence should include the date, time, location, examiner, and weather conditions at recovery.

Footwear impression comparison should consider the possibility of a different shoe with the same pattern; class characteristics alone cannot identify a specific shoe.

Tire track evidence should be compared with the vehicle's tire specifications, including size, track width, and wheelbase, to support or exclude a vehicle.

Impression evidence should be collected before the scene is released; fragile impressions can be destroyed by weather or traffic.

Footwear and tire evidence should be documented with a sketch and photographs; the sketch should show the location and orientation of each impression.

Report conclusions should be stated using a defined scale and the basis for the conclusion should be explained.

Footwear impression evidence can be used to link a suspect to a scene, but the strength of the link depends on the number and quality of individual characteristics.

Tire track evidence can be used to reconstruct the vehicle's path and speed; the reconstruction should state the assumptions and limitations.

Impression evidence should be retained and available for review; the original casts, lifts, and photographs are the primary record.

Footwear impression evidence can be used to support a reconstruction of the event; the location and orientation of impressions relative to other evidence are relevant.

Tire track evidence can be used to support a reconstruction of the vehicle's movement; the track's position and direction are relevant.

Impression evidence should be collected with appropriate techniques for the medium; the technique should be documented.

Footwear and tire evidence should be packaged and stored to prevent contamination and damage.

Report conclusions should be based on a documented examination and should state the limitations of the evidence.

Footwear impression evidence can be used to support or refute a statement; the comparison should be based on the actual exemplar.

Tire track evidence can be used to identify the vehicle class and, with individual characteristics, a specific vehicle.

Documentation of impression evidence should include the examiner's notes, photographs, and measurements.

Footwear impression evidence should be examined using a systematic approach: class characteristics, wear, and individual characteristics.

Tire track evidence should be examined using a systematic approach: track width, wheelbase, tread pattern, and individual tire characteristics.

Impression evidence should be photographed with scale and oblique lighting to reveal detail.

Footwear and tire evidence should be collected and packaged to preserve detail and prevent contamination.

Report conclusions should be stated using a defined scale and should explain the basis for the conclusion.

Footwear impression evidence can be used to link a suspect to a scene; the strength of the link depends on the individual characteristics.

Tire track evidence can be used to link a vehicle to a scene; the strength of the link depends on the individual tire characteristics.

Documentation of impression evidence should include the location, orientation, and relationship to other evidence.

Footwear impression evidence can be used to support a reconstruction of the event; the location and orientation of impressions relative to other evidence are relevant.

Tire track evidence can be used to support a reconstruction of the vehicle's movement; the track's position and direction are relevant.

Impression evidence should be collected with appropriate techniques for the medium; the technique should be documented.

Footwear and tire evidence should be packaged and stored to prevent contamination and damage.

Report conclusions should be based on a documented examination and should state the limitations of the evidence.

Footwear impression evidence can be used to support or refute a statement; the comparison should be based on the actual exemplar.

Tire track evidence can be used to identify the vehicle class and, with individual characteristics, a specific vehicle.

Documentation of impression evidence should include the examiner's notes, photographs, and measurements.

Footwear impression evidence should be examined using a systematic approach: class characteristics, wear, and individual characteristics.

Tire track evidence should be examined using a systematic approach: track width, wheelbase, tread pattern, and individual tire characteristics.

Impression evidence should be photographed with scale and oblique lighting to reveal detail.

Footwear and tire evidence should be collected and packaged to preserve detail and prevent contamination.

Report conclusions should be stated using a defined scale and should explain the basis for the conclusion.

Footwear impression evidence can be used to link a suspect to a scene; the strength of the link depends on the individual characteristics.

Tire track evidence can be used to link a vehicle to a scene; the strength of the link depends on the individual tire characteristics.

Documentation of impression evidence should include the location, orientation, and relationship to other evidence.