IAI CP2 cheat sheet

Impact spatter: stains are generally 1–4 mm; fine spatter under 1 mm indicates high-velocity impact (gunshot, machinery, explosion); medium velocity 1–4 mm (blunt force, stabbing); low velocity greater than 4 mm (dripping, bleeding under gravity).

Satellite spatter: small droplets that separate from a parent drop on impact; they travel further and land distal to the parent stain, and their direction of travel follows the parent drop's trajectory.

Angle of impact formula: sin θ = width/length of an elliptical stain, where length is the major axis along the direction of travel and width is the minor axis. A circular stain (width = length) means 90° impact.

Directionality: the pointed, 'tail' end of an elliptical or exclamation-mark stain faces the direction of travel; the rounded end faces the origin. The tail points away from the impact source.

Area of origin (3D): determine the impact angle for at least two stains in a pattern, draw lines through their long axes in the horizontal plane, intersect to find the area of convergence, then compute height: Z = tan θ × horizontal distance from the convergence point to the stain.

Cast-off: blood flung from a bloodied object in motion, producing linear trails of stains; the number and spacing of trails relate to the number of blows or swings and the arc of the weapon.

Arterial gush/spurt: stains produced by a breached artery, showing a repeating, rhythmic pattern of large droplets or a spray whose spacing follows the cardiac cycle; often appears on vertical surfaces.

Expirated blood: fine mist mixed with air from the nose/mouth, often with bubbles or mucus; distinguished from impact spatter by its distribution and by the presence of air bubbles or saliva.

Void patterns: absence of bloodstain in an otherwise bloodstained area, indicating an object or person was present during the bloodshed and later removed; outlines the shape of the missing object.

Drip patterns: free-falling drops produce circular stains on horizontal surfaces; on inclined surfaces they elongate. A drop falling from greater height produces a larger stain and more satellite spatter.

Transfer patterns: contact between a blood-bearing object and a surface; the resulting stain mirrors the shape/texture of the object (e.g., shoe tread, fabric weave, fingerprint).

Swipe vs. wipe: a swipe is transfer of blood from a moving bloodied object onto a clean surface; a wipe is a moving clean object through wet blood, often showing lighter streaks and feathering.

Blood volume estimation: a single drop typically holds about 0.05 mL; a stain's volume can be estimated from its diameter using known drop-size relationships, but the method is approximate and affected by surface porosity.

Surface effects: porous surfaces (wood, fabric) wick and distort stains, reducing edge sharpness; non-porous surfaces (glass, tile, metal) preserve sharp edges and reliable angle measurements.

Sequence and superimposition: a stain that overlies another is generally later; overlapping stains, spatter on top of a transfer, and direction of spatter through a stain establish relative timing.

Documentation: photograph with and without a scale, take overall/mid-range/close-up images, measure stain dimensions, and record surface type and orientation before any collection.

Presumptive tests: luminol (chemiluminescence) and fluorescein detect latent blood; confirmatory tests (e.g., Takayama, ABAcard) are needed to establish blood, and DNA analysis identifies the donor.

Terminology: 'spatter' refers to blood dispersed by force; 'stain' is any blood deposit. Use consistent terminology such as 'impact pattern', 'cast-off pattern', 'flow pattern', and 'pool' to avoid ambiguity.

Flow patterns: blood moving under gravity along a surface; direction is indicated by the leading edge and by the trail left behind. Flow on a vertical surface indicates the surface's orientation at the time of deposition.

Pooling: blood collecting in a depression or on a horizontal surface; a pool's shape and edges can indicate whether the surface was level or tilted and whether the body was moved.

Point of origin vs. point of convergence: convergence is the 2D intersection of trajectory lines; origin is the 3D location above it, requiring impact angles and height calculations.

Stringing method: physically run strings from stains through the point of convergence to the calculated height; this is a demonstrative tool, not a measurement substitute for trigonometric calculation.

Limitations: BPA is reconstructive and probabilistic; it cannot by itself identify a person, determine intent, or reliably establish time of deposition. Conclusions should be stated with confidence levels.

Exclusion: patterns that mimic blood (paint, rust, food, ketchup) and patterns that mimic spatter (insect activity, sneezing, coughing, dripping from a ceiling) must be ruled out before interpretation.

Report writing: state the pattern type, the basis for classification, the measurements used, the calculated angle/origin, and the limitations; distinguish observation from interpretation.

Terminal velocity and drop size: drop size is determined mainly by the surface tension and the object from which it falls; free-falling drops reach terminal velocity after roughly 2 m, so stains from greater heights do not grow proportionally.

Angle calculation example: a stain 12 mm long and 6 mm wide gives sin θ = 6/12 = 0.5, so θ = 30°. A stain 10 mm long and 10 mm wide gives 90°.

Height calculation example: if the horizontal distance from the convergence point to a stain is 40 cm and the impact angle is 30°, the height Z = tan 30° × 40 cm ≈ 0.577 × 40 ≈ 23 cm above the surface.

Droplet size: a typical blood drop is about 0.05 mL and about 4–5 mm in diameter when deposited on a non-porous horizontal surface from a low height.

Drying and color: fresh blood is red; drying shifts color toward brown/black. Drying time depends on volume, surface, temperature, and humidity, so color alone cannot date a stain.

Impact direction: impact spatter radiates outward from the impact site; the pattern's shape and the distribution of stains help locate the impact point on a surface or object.

Cast-off geometry: cast-off trails are linear and often parallel, with the direction of the swing indicated by the shape and orientation of the individual stains.

Chain of custody: document each item, its location, and the collection method; bloodstained items should be air-dried before packaging to prevent degradation and contamination.

Camera and scale: use a tripod, level the camera to the stain plane, and include an ABFO-type scale in the same plane as the stain to avoid perspective error in measurement.

Lighting: oblique or raking light reveals faint stains and texture; diffuse light reduces glare on non-porous surfaces; UV light can reveal cleaned or latent blood when used with appropriate filters.

Measurement precision: record major and minor axes to the nearest millimeter; take multiple measurements of the same stain and average to reduce error.

Pattern classification: classify by mechanism (impact, cast-off, transfer, flow, drip, expiration, arterial, void) rather than by appearance alone; a single pattern may have multiple mechanisms.

Bloodstain on fabric: fabric texture causes wicking and distortion; stains on fabric are generally less reliable for angle calculations than stains on hard, non-porous surfaces.

Reconstruction: combine BPA with scene geometry, photographs, and witness statements; the analyst should state assumptions (e.g., surface orientation at the time of the event).

Quality assurance: peer review, documented methodology, and calibrated instruments are expected; the analyst should be able to explain each step from observation to conclusion.

Impact spatter size ranges: low velocity greater than 4 mm, medium velocity 1–4 mm, high velocity less than 1 mm; these ranges are guidelines, not absolute thresholds.

Direction of travel: the tail of an exclamation-mark stain points in the direction of travel; the rounded end points toward the origin.

Angle of impact: sin θ = width/length; θ = 90° for circular stains, approaching 0° for long, thin stains.

Area of convergence: intersect lines drawn through the long axes of stains in the horizontal plane; the intersection is the point of convergence.

Area of origin: Z = tan θ × horizontal distance from the convergence point to the stain; repeat for multiple stains and compare.

Drip: free-falling drops produce circular stains on horizontal surfaces; larger drops and greater heights produce larger stains and more satellite spatter.

Transfer: contact between a bloodied object and a surface; the stain shape reflects the object (tread, fabric weave, fingerprint).

Void: absence of blood in an otherwise bloodstained area, indicating an object or person was present and later removed.

Documentation: overall, mid-range, and close-up photographs with a scale; record surface type, orientation, and measurements before collection.

Arterial spurt: rhythmic, repeating pattern of droplets or spray following the cardiac cycle; often on vertical surfaces and may show a 'spurting' arc.

Expirated blood: fine mist from the nose/mouth, often with air bubbles or mucus; distinguished from impact spatter by distribution and by the presence of bubbles or saliva.

Cast-off: blood flung from a moving bloodied object; linear trails of stains whose number and spacing relate to the number of blows or swings.

Flow: blood moving under gravity along a surface; direction indicated by the leading edge and the trail left behind.

Pool: blood collecting in a depression or on a horizontal surface; the pool's shape and edges can indicate whether the surface was level or tilted.

Swipe vs. wipe: a swipe is transfer from a moving bloodied object onto a clean surface; a wipe is a moving clean object through wet blood, often showing lighter streaks and feathering.

Superimposition: a stain that overlies another is generally later; overlapping stains establish relative timing.

Limitations: BPA cannot identify a person, determine intent, or reliably establish time of deposition; conclusions should be stated with confidence levels.

Presumptive tests: luminol and fluorescein detect latent blood; confirmatory tests (e.g., Takayama, ABAcard) establish blood; DNA analysis identifies the donor.

Luminol: chemiluminescence reveals cleaned or latent blood; it is destructive to some evidence and should be used after other collection methods.

Chain of custody: document each item, its location, and the collection method; air-dry bloodstained items before packaging to prevent degradation and contamination.

Surface porosity: porous surfaces (wood, fabric) wick and distort stains, reducing edge sharpness; non-porous surfaces (glass, tile, metal) preserve sharp edges and reliable angle measurements.

Photography: use a tripod, level the camera to the stain plane, and include a scale in the same plane as the stain to avoid perspective error.

Lighting: oblique or raking light reveals faint stains and texture; diffuse light reduces glare on non-porous surfaces; UV light can reveal cleaned or latent blood with appropriate filters.

Measurement precision: record major and minor axes to the nearest millimeter; take multiple measurements and average to reduce error.

Report writing: state the pattern type, the basis for classification, the measurements used, the calculated angle/origin, and the limitations; distinguish observation from interpretation.

Impact spatter: stains generally 1–4 mm; fine spatter under 1 mm indicates high-velocity impact (gunshot, machinery, explosion); medium velocity 1–4 mm (blunt force, stabbing); low velocity greater than 4 mm (dripping, bleeding under gravity).

Satellite spatter: small droplets that separate from a parent drop on impact; they travel further and land distal to the parent stain, and their direction of travel follows the parent drop's trajectory.

Angle of impact formula: sin θ = width/length of an elliptical stain, where length is the major axis along the direction of travel and width is the minor axis. A circular stain (width = length) means 90° impact.

Directionality: the pointed, 'tail' end of an elliptical or exclamation-mark stain faces the direction of travel; the rounded end faces the origin. The tail points away from the impact source.

Area of origin (3D): determine the impact angle for at least two stains in a pattern, draw lines through their long axes in the horizontal plane, intersect to find the area of convergence, then compute height: Z = tan θ × horizontal distance from the convergence point to the stain.

Cast-off: blood flung from a bloodied object in motion, producing linear trails of stains; the number and spacing of trails relate to the number of blows or swings and the arc of the weapon.

Arterial gush/spurt: stains produced by a breached artery, showing a repeating, rhythmic pattern of large droplets or a spray whose spacing follows the cardiac cycle; often appears on vertical surfaces.

Expirated blood: fine mist mixed with air from the nose/mouth, often with bubbles or mucus; distinguished from impact spatter by its distribution and by the presence of air bubbles or saliva.

Void patterns: absence of bloodstain in an otherwise bloodstained area, indicating an object or person was present during the bloodshed and later removed; outlines the shape of the missing object.

Drip patterns: free-falling drops produce circular stains on horizontal surfaces; on inclined surfaces they elongate. A drop falling from greater height produces a larger stain and more satellite spatter.

Transfer patterns: contact between a blood-bearing object and a surface; the resulting stain mirrors the shape/texture of the object (e.g., shoe tread, fabric weave, fingerprint).

Swipe vs. wipe: a swipe is transfer of blood from a moving bloodied object onto a clean surface; a wipe is a moving clean object through wet blood, often showing lighter streaks and feathering.

Blood volume estimation: a single drop typically holds about 0.05 mL; a stain's volume can be estimated from its diameter using known drop-size relationships, but the method is approximate and affected by surface porosity.

Surface effects: porous surfaces (wood, fabric) wick and distort stains, reducing edge sharpness; non-porous surfaces (glass, tile, metal) preserve sharp edges and reliable angle measurements.

Sequence and superimposition: a stain that overlies another is generally later; overlapping stains, spatter on top of a transfer, and direction of spatter through a stain establish relative timing.

Documentation: photograph with and without a scale, take overall/mid-range/close-up images, measure stain dimensions, and record surface type and orientation before any collection.

Presumptive tests: luminol (chemiluminescence) and fluorescein detect latent blood; confirmatory tests (e.g., Takayama, ABAcard) are needed to establish blood, and DNA analysis identifies the donor.

Terminology: 'spatter' refers to blood dispersed by force; 'stain' is any blood deposit. Use consistent terminology such as 'impact pattern', 'cast-off pattern', 'flow pattern', and 'pool' to avoid ambiguity.

Flow patterns: blood moving under gravity along a surface; direction is indicated by the leading edge and by the trail left behind. Flow on a vertical surface indicates the surface's orientation at the time of deposition.

Pooling: blood collecting in a depression or on a horizontal surface; a pool's shape and edges can indicate whether the surface was level or tilted and whether the body was moved.

Point of origin vs. point of convergence: convergence is the 2D intersection of trajectory lines; origin is the 3D location above it, requiring impact angles and height calculations.

Stringing method: physically run strings from stains through the point of convergence to the calculated height; this is a demonstrative tool, not a measurement substitute for trigonometric calculation.

Limitations: BPA is reconstructive and probabilistic; it cannot by itself identify a person, determine intent, or reliably establish time of deposition. Conclusions should be stated with confidence levels.

Exclusion: patterns that mimic blood (paint, rust, food, ketchup) and patterns that mimic spatter (insect activity, sneezing, coughing, dripping from a ceiling) must be ruled out before interpretation.

Report writing: state the pattern type, the basis for classification, the measurements used, the calculated angle/origin, and the limitations; distinguish observation from interpretation.

Terminal velocity and drop size: drop size is determined mainly by the surface tension and the object from which it falls; free-falling drops reach terminal velocity after roughly 2 m, so stains from greater heights do not grow proportionally.

Angle calculation example: a stain 12 mm long and 6 mm wide gives sin θ = 6/12 = 0.5, so θ = 30°. A stain 10 mm long and 10 mm wide gives 90°.

Height calculation example: if the horizontal distance from the convergence point to a stain is 40 cm and the impact angle is 30°, the height Z = tan 30° × 40 cm ≈ 0.577 × 40 ≈ 23 cm above the surface.

Droplet size: a typical blood drop is about 0.05 mL and about 4–5 mm in diameter when deposited on a non-porous horizontal surface from a low height.

Drying and color: fresh blood is red; drying shifts color toward brown/black. Drying time depends on volume, surface, temperature, and humidity, so color alone cannot date a stain.

Impact direction: impact spatter radiates outward from the impact site; the pattern's shape and the distribution of stains help locate the impact point on a surface or object.

Cast-off geometry: cast-off trails are linear and often parallel, with the direction of the swing indicated by the shape and orientation of the individual stains.

Chain of custody: document each item, its location, and the collection method; bloodstained items should be air-dried before packaging to prevent degradation and contamination.

Camera and scale: use a tripod, level the camera to the stain plane, and include an ABFO-type scale in the same plane as the stain to avoid perspective error in measurement.

Lighting: oblique or raking light reveals faint stains and texture; diffuse light reduces glare on non-porous surfaces; UV light can reveal cleaned or latent blood when used with appropriate filters.

Measurement precision: record major and minor axes to the nearest millimeter; take multiple measurements of the same stain and average to reduce error.

Pattern classification: classify by mechanism (impact, cast-off, transfer, flow, drip, expiration, arterial, void) rather than by appearance alone; a single pattern may have multiple mechanisms.

Bloodstain on fabric: fabric texture causes wicking and distortion; stains on fabric are generally less reliable for angle calculations than stains on hard, non-porous surfaces.

Reconstruction: combine BPA with scene geometry, photographs, and witness statements; the analyst should state assumptions (e.g., surface orientation at the time of the event).

Quality assurance: peer review, documented methodology, and calibrated instruments are expected; the analyst should be able to explain each step from observation to conclusion.

Impact spatter size ranges: low velocity greater than 4 mm, medium velocity 1–4 mm, high velocity less than 1 mm; these ranges are guidelines, not absolute thresholds.

Direction of travel: the tail of an exclamation-mark stain points in the direction of travel; the rounded end points toward the origin.

Angle of impact: sin θ = width/length; θ = 90° for circular stains, approaching 0° for long, thin stains.

Area of convergence: intersect lines drawn through the long axes of stains in the horizontal plane; the intersection is the point of convergence.

Area of origin: Z = tan θ × horizontal distance from the convergence point to the stain; repeat for multiple stains and compare.

Drip: free-falling drops produce circular stains on horizontal surfaces; larger drops and greater heights produce larger stains and more satellite spatter.

Transfer: contact between a bloodied object and a surface; the stain shape reflects the object (tread, fabric weave, fingerprint).

Void: absence of blood in an otherwise bloodstained area, indicating an object or person was present and later removed.

Documentation: overall, mid-range, and close-up photographs with a scale; record surface type, orientation, and measurements before collection.

Arterial spurt: rhythmic, repeating pattern of droplets or spray following the cardiac cycle; often on vertical surfaces and may show a 'spurting' arc.

Expirated blood: fine mist from the nose/mouth, often with air bubbles or mucus; distinguished from impact spatter by distribution and by the presence of bubbles or saliva.

Cast-off: blood flung from a moving bloodied object; linear trails of stains whose number and spacing relate to the number of blows or swings.

Flow: blood moving under gravity along a surface; direction indicated by the leading edge and the trail left behind.

Pool: blood collecting in a depression or on a horizontal surface; the pool's shape and edges can indicate whether the surface was level or tilted.

Swipe vs. wipe: a swipe is transfer from a moving bloodied object onto a clean surface; a wipe is a moving clean object through wet blood, often showing lighter streaks and feathering.

Superimposition: a stain that overlies another is generally later; overlapping stains establish relative timing.

Limitations: BPA cannot identify a person, determine intent, or reliably establish time of deposition; conclusions should be stated with confidence levels.

Presumptive tests: luminol and fluorescein detect latent blood; confirmatory tests (e.g., Takayama, ABAcard) establish blood; DNA analysis identifies the donor.

Luminol: chemiluminescence reveals cleaned or latent blood; it is destructive to some evidence and should be used after other collection methods.

Chain of custody: document each item, its location, and the collection method; air-dry bloodstained items before packaging to prevent degradation and contamination.

Surface porosity: porous surfaces (wood, fabric) wick and distort stains, reducing edge sharpness; non-porous surfaces (glass, tile, metal) preserve sharp edges and reliable angle measurements.

Photography: use a tripod, level the camera to the stain plane, and include a scale in the same plane as the stain to avoid perspective error.

Lighting: oblique or raking light reveals faint stains and texture; diffuse light reduces glare on non-porous surfaces; UV light can reveal cleaned or latent blood with appropriate filters.

Measurement precision: record major and minor axes to the nearest millimeter; take multiple measurements and average to reduce error.

Report writing: state the pattern type, the basis for classification, the measurements used, the calculated angle/origin, and the limitations; distinguish observation from interpretation.

Impact spatter: stains generally 1–4 mm; fine spatter under 1 mm indicates high-velocity impact (gunshot, machinery, explosion); medium velocity 1–4 mm (blunt force, stabbing); low velocity greater than 4 mm (dripping, bleeding under gravity).

Satellite spatter: small droplets that separate from a parent drop on impact; they travel further and land distal to the parent stain, and their direction of travel follows the parent drop's trajectory.

Angle of impact formula: sin θ = width/length of an elliptical stain, where length is the major axis along the direction of travel and width is the minor axis. A circular stain (width = length) means 90° impact.

Directionality: the pointed, 'tail' end of an elliptical or exclamation-mark stain faces the direction of travel; the rounded end faces the origin. The tail points away from the impact source.

Area of origin (3D): determine the impact angle for at least two stains in a pattern, draw lines through their long axes in the horizontal plane, intersect to find the area of convergence, then compute height: Z = tan θ × horizontal distance from the convergence point to the stain.

Cast-off: blood flung from a bloodied object in motion, producing linear trails of stains; the number and spacing of trails relate to the number of blows or swings and the arc of the weapon.

Arterial gush/spurt: stains produced by a breached artery, showing a repeating, rhythmic pattern of large droplets or a spray whose spacing follows the cardiac cycle; often appears on vertical surfaces.

Expirated blood: fine mist mixed with air from the nose/mouth, often with bubbles or mucus; distinguished from impact spatter by its distribution and by the presence of air bubbles or saliva.

Void patterns: absence of bloodstain in an otherwise bloodstained area, indicating an object or person was present during the bloodshed and later removed; outlines the shape of the missing object.

Drip patterns: free-falling drops produce circular stains on horizontal surfaces; on inclined surfaces they elongate. A drop falling from greater height produces a larger stain and more satellite spatter.

Transfer patterns: contact between a blood-bearing object and a surface; the resulting stain mirrors the shape/texture of the object (e.g., shoe tread, fabric weave, fingerprint).

Swipe vs. wipe: a swipe is transfer of blood from a moving bloodied object onto a clean surface; a wipe is a moving clean object through wet blood, often showing lighter streaks and feathering.

Blood volume estimation: a single drop typically holds about 0.05 mL; a stain's volume can be estimated from its diameter using known drop-size relationships, but the method is approximate and affected by surface porosity.

Surface effects: porous surfaces (wood, fabric) wick and distort stains, reducing edge sharpness; non-porous surfaces (glass, tile, metal) preserve sharp edges and reliable angle measurements.

Sequence and superimposition: a stain that overlies another is generally later; overlapping stains, spatter on top of a transfer, and direction of spatter through a stain establish relative timing.

Documentation: photograph with and without a scale, take overall/mid-range/close-up images, measure stain dimensions, and record surface type and orientation before any collection.

Presumptive tests: luminol (chemiluminescence) and fluorescein detect latent blood; confirmatory tests (e.g., Takayama, ABAcard) are needed to establish blood, and DNA analysis identifies the donor.