IAI CBPA cheat sheet

Surface texture governs stain shape: rough or porous targets produce satellite spatter and irregular margins, smooth non-porous targets preserve circularity and edge definition.

Impact angle follows sin θ = width/length, where θ is measured from the target surface plane; a stain with equal width and length indicates a 90° (perpendicular) impact.

Directionality is read from the elliptical stain's long axis and the tapered, spine-like end pointing away from the point of origin; the tail points in the direction of travel.

Area of origin is derived by projecting a line through each stain's long axis back from the impact site; the intersection of multiple lines (stringing) locates the origin in three dimensions.

Drop volume influences stain diameter: a typical 0.05 mL blood drop falling from about 1 m onto a smooth surface yields a stain roughly 10-13 mm in diameter; larger stains suggest larger volume or greater height.

Drip patterns show vertically aligned, similarly sized stains with occasional satellite spatter; cast-off patterns show linear trails of decreasing-size stains along an arc, tracking the weapon's swing.

Arterial damage produces gushing, pulsating patterns with large volumes and spine-like projections, often on vertical surfaces; expiration (exhaled) patterns appear as fine mist-like droplets near the nose or mouth.

Void patterns are absence of staining where an object or person blocked blood deposition; they mark the position of an intervening object during the event.

Bloodstain pattern analysis classifies stains as passive (drip, flow, pool), spatter (impact, cast-off, arterial, expiration), and altered (wiped, diluted, absorbed); pattern classification precedes any reconstruction.

Passive stains form under gravity or capillary action; flow stains follow surface contours and pool at low points, indicating orientation of the surface at deposition.

Spatter is defined by droplet size and distribution: impact spatter generally ranges from 1-4 mm for high-velocity to larger droplets for low-velocity; velocity terminology is descriptive, not a strict energy measurement.

The point of convergence is a two-dimensional construct on the target plane; the point of origin adds height and requires angle measurements from at least two stains.

Wipe patterns result from a lateral motion through wet blood, smearing it; swipe patterns result from an object moving through wet blood and then contacting another surface.

Transfer stains record the shape of the contacting object (e.g., fabric weave, shoe tread) and can identify the object and its orientation at contact.

Blood volume estimation uses stain area and known spread factors per surface; porous surfaces absorb and spread more, so volume estimates are less reliable there.

Documentation sequence: overall, mid-range, and close-up photographs with a scale and color reference; sketches record measurement geometry before any reconstruction.

Chemical enhancement (luminol, fluorescein, leuco crystal violet) detects latent blood but can dilute or alter stains; photograph before and after application and record reagent use.

DNA and pattern analysis are independent lines of evidence; pattern interpretation must not be used to infer individual identity, only the mechanics of deposition.

Terminal velocity of a falling blood drop is reached at roughly 6-7 m of fall; beyond that height stain diameter no longer increases, so height cannot be inferred from stain size alone.

Droplet size from impact spatter correlates with energy: fine mist (under 1 mm) suggests high-energy mechanisms such as gunshot, explosion, or power tools.

Cast-off patterns from a swinging weapon produce a line of stains whose spacing and size decrease along the arc as blood is depleted.

A single blow rarely produces cast-off; multiple blows typically produce multiple cast-off trails, so trail counts can inform blow counts.

Expirated blood contains air bubbles and mucus, appears as fine droplets, and often shows a diluted or frothy appearance; it can be confused with impact spatter.

Blood pooling indicates a victim remained stationary; the pool's shape and flow direction can establish body position and subsequent movement.

Drying times depend on temperature, humidity, surface, and volume; dried stains crack and flake, and re-wetting produces a tide mark (halo) at the edge.

Sequencing is inferred from overlapping stains: the later stain lies on top and interrupts the earlier one; skeletonized stains indicate an earlier deposit overlaid by a later one.

Contamination control requires gloves, clean instruments, and separate packaging of reference samples; bloodstain evidence is biological evidence and subject to chain-of-custody rules.

Angle of impact calculation: measure length (L) and width (W) of the ellipse, then θ = arcsin(W/L); record measurements in millimeters with a calibrated scale.

A stain with W/L = 0.5 corresponds to a 30° impact angle; W/L = 0.71 corresponds to 45°; W/L = 1.0 corresponds to 90°.

Direction of travel is opposite the pointed end of the stain; the tail indicates the droplet's motion vector projected onto the surface.

Point of origin height = tan(impact angle) × distance from the stain to the point of convergence, measured on the target surface.

A minimum of two stains is required for a point of origin, but three or more are preferred to assess error and consistency.

Impact spatter radiates outward and upward from a source; stains on vertical surfaces near the impact show upward directionality.

Satellite spatter consists of small droplets surrounding a parent stain, formed when the parent drop breaks up on impact; satellites are not independent stains for reconstruction.

Blood on a weapon's leading edge versus trailing edge can distinguish forward from backward swing direction in cast-off analysis.

Reported conclusions should state the pattern type, the mechanism, and the confidence level; pattern analysis cannot determine timing of individual blows with certainty.

Drip patterns: stains of similar size aligned vertically, with satellites; a falling drop from a stationary source produces a round stain on a horizontal surface.

Impact patterns: radiating spatter with a central void or dense core; the size distribution reflects the energy of the impact.

Arterial spatter: large volume, gushing, and spine-like projections; the pattern can show pulsatile spacing if the victim moved.

Expirated patterns: fine droplets, bubbles, and mucus, concentrated near the airway; often found on surfaces close to the face.

Transfer patterns: contact impressions such as footwear, fabric, or handprints; the pattern shape mirrors the contacting object.

Wipe and swipe: wipe = motion through wet blood on a surface; swipe = object with blood contacting a clean surface; both are transfer mechanisms.

Void patterns: absence of blood in an otherwise stained area; a void can indicate a body, weapon, or furniture position during the event.

Altered stains: dilution, absorption, and removal; interpretation must account for post-event cleaning, fire, or decomposition.

Reconstruction combines pattern classification, angle measurements, and scene geometry; the final report should separate observation from inference.

Blood is a non-Newtonian fluid; its behavior on impact depends on droplet size, velocity, and surface, so identical mechanisms can yield different stain shapes on different surfaces.

Surface roughness increases satellite spatter and reduces stain circularity; smooth glass or tile gives the most reliable angle measurements.

Porous surfaces (wood, fabric, concrete) absorb blood and distort stain shape; angle-of-impact calculations on porous surfaces are less reliable.

Bloodstain evidence should be photographed with a scale and a color reference; measurements should be recorded before any enhancement or collection.

Luminol and other reagents can dilute DNA and alter stain appearance; document the untreated scene first and record all reagent applications.

Chain of custody must be maintained for bloodstain evidence, including swabs, reference samples, and controls; contamination can invalidate DNA results.

Pattern analysis is a tool for reconstruction, not identification; DNA and serology determine identity, while pattern analysis determines mechanics.

Peer review and independent verification of angle measurements and origin calculations reduce error and are standard practice in casework.

Court testimony should explain the basis for each conclusion, the limitations of the method, and the distinction between consistent and conclusive findings.

Droplet diameter from a falling drop increases with height up to terminal velocity, then plateaus; stain size alone cannot establish fall height without controlled experiments.

Impact spatter droplet size decreases with increasing energy; high-velocity spatter (fine mist) is associated with gunshot and explosive mechanisms.

Cast-off stains are elongated and aligned along the swing arc; the direction of the tail indicates the direction of the weapon's motion.

Arterial patterns show large, gushing stains with spine-like projections; the pulsatile pattern can indicate the victim's position and movement.

Expirated patterns contain air bubbles and mucus and are concentrated near the airway; they can be mistaken for impact spatter.

Void patterns mark the position of an object or person that blocked blood deposition; voids are interpreted relative to surrounding stains.

Sequencing by overlap: the later stain interrupts the earlier one; skeletonization indicates an earlier stain partially covered by a later one.

Drying and re-wetting produce tide marks; the presence of a halo can indicate a second wetting event.

Reconstruction requires at least two stains for convergence and three or more for a reliable origin; error analysis should accompany the result.

Angle of impact: θ = arcsin(W/L); measure the ellipse's width and length at the widest and longest points, respectively.

Point of convergence: draw lines through the long axes of stains; their intersection is the 2D convergence point on the target surface.

Point of origin: height = tan(θ) × distance from stain to convergence; the origin is the 3D source of the spatter.

Directionality: the tail of the stain points in the direction of droplet travel; the long axis aligns with the trajectory.

Stain diameter from a falling drop: about 10-13 mm for a 0.05 mL drop from 1 m on a smooth surface; larger stains suggest greater volume or height.

Terminal velocity: reached at roughly 6-7 m of fall; beyond this, stain size does not increase with height.

Impact angle reference: W/L = 0.5 → 30°; W/L = 0.71 → 45°; W/L = 1.0 → 90°.

Spatter classification: passive (drip, flow, pool), spatter (impact, cast-off, arterial, expiration), and altered (wipe, swipe, dilution, absorption).

Documentation: overall, mid-range, and close-up photographs with scale and color reference; sketches and measurements before enhancement or collection.

Impact spatter radiates from the source; stains on vertical surfaces near the impact show upward directionality and elongated shapes.

Cast-off trails: multiple blows produce multiple trails; the number of trails can inform the number of blows, but not with certainty.

Arterial damage: gushing, pulsatile patterns with large volume; the pattern can indicate the victim's position and movement.

Expiration: fine droplets with bubbles and mucus near the airway; often found on surfaces close to the face.

Transfer: contact impressions such as footwear, fabric, or handprints; the pattern shape mirrors the contacting object.

Wipe: lateral motion through wet blood smears it; swipe: an object with blood contacts a clean surface, leaving a transfer.

Void: absence of blood in an otherwise stained area; a void can indicate a body, weapon, or furniture position during the event.

Altered stains: dilution, absorption, and removal; interpretation must account for cleaning, fire, or decomposition.

Reconstruction combines pattern classification, angle measurements, and scene geometry; separate observation from inference in the report.

Blood is a non-Newtonian fluid; its behavior on impact depends on droplet size, velocity, and surface, so identical mechanisms can yield different stain shapes.

Surface roughness increases satellite spatter and reduces stain circularity; smooth glass or tile gives the most reliable angle measurements.

Porous surfaces absorb blood and distort stain shape; angle-of-impact calculations on porous surfaces are less reliable.

Photograph with a scale and color reference; record measurements before enhancement or collection.

Luminol and other reagents can dilute DNA and alter stain appearance; document the untreated scene first.

Chain of custody must be maintained for bloodstain evidence, including swabs, reference samples, and controls.

Pattern analysis is a tool for reconstruction, not identification; DNA and serology determine identity.

Peer review and independent verification of angle measurements and origin calculations reduce error.

Court testimony should explain the basis for each conclusion, the limitations of the method, and the distinction between consistent and conclusive findings.

Droplet diameter from a falling drop increases with height up to terminal velocity, then plateaus; stain size alone cannot establish fall height.

Impact spatter droplet size decreases with increasing energy; fine mist is associated with gunshot and explosive mechanisms.

Cast-off stains are elongated and aligned along the swing arc; the tail indicates the direction of the weapon's motion.

Arterial patterns show large, gushing stains with spine-like projections; the pulsatile pattern can indicate the victim's position and movement.

Expirated patterns contain air bubbles and mucus and are concentrated near the airway; they can be mistaken for impact spatter.

Void patterns mark the position of an object or person that blocked blood deposition.

Sequencing by overlap: the later stain interrupts the earlier one; skeletonization indicates an earlier stain partially covered by a later one.

Drying and re-wetting produce tide marks; the presence of a halo can indicate a second wetting event.

Reconstruction requires at least two stains for convergence and three or more for a reliable origin; error analysis should accompany the result.

Angle of impact: θ = arcsin(W/L); measure the ellipse's width and length at the widest and longest points.

Point of convergence: draw lines through the long axes of stains; their intersection is the 2D convergence point.

Point of origin: height = tan(θ) × distance from stain to convergence; the origin is the 3D source of the spatter.

Directionality: the tail of the stain points in the direction of droplet travel; the long axis aligns with the trajectory.

Stain diameter from a falling drop: about 10-13 mm for a 0.05 mL drop from 1 m on a smooth surface.

Terminal velocity: reached at roughly 6-7 m of fall; beyond this, stain size does not increase with height.

Impact angle reference: W/L = 0.5 → 30°; W/L = 0.71 → 45°; W/L = 1.0 → 90°.

Spatter classification: passive (drip, flow, pool), spatter (impact, cast-off, arterial, expiration), and altered (wipe, swipe, dilution, absorption).

Documentation: overall, mid-range, and close-up photographs with scale and color reference; sketches and measurements before enhancement or collection.

Impact spatter radiates from the source; stains on vertical surfaces near the impact show upward directionality and elongated shapes.

Cast-off trails: multiple blows produce multiple trails; the number of trails can inform the number of blows, but not with certainty.

Arterial damage: gushing, pulsatile patterns with large volume; the pattern can indicate the victim's position and movement.

Expiration: fine droplets with bubbles and mucus near the airway; often found on surfaces close to the face.

Transfer: contact impressions such as footwear, fabric, or handprints; the pattern shape mirrors the contacting object.

Wipe: lateral motion through wet blood smears it; swipe: an object with blood contacts a clean surface, leaving a transfer.

Void: absence of blood in an otherwise stained area; a void can indicate a body, weapon, or furniture position during the event.

Altered stains: dilution, absorption, and removal; interpretation must account for cleaning, fire, or decomposition.

Reconstruction combines pattern classification, angle measurements, and scene geometry; separate observation from inference in the report.