IAI CBPA flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

Angle of impact formula

θ = arcsin(W/L), where W is the ellipse width and L is the ellipse length. The angle is measured from the target surface plane, so a circular stain gives 90 degrees.

Point of convergence

The two-dimensional point on a target surface where lines drawn through the long axes of multiple bloodstains intersect. It locates the source position in the plane of the surface.

Point of origin

The three-dimensional location of the blood source. Height above the convergence point equals tan of the impact angle multiplied by the distance from the stain to the convergence point.

Directionality of a stain

The tapered tail of an elongated stain points in the direction the droplet was traveling. The long axis aligns with the trajectory projected onto the target surface.

Terminal velocity of blood drops

A falling blood drop reaches terminal velocity after roughly six to seven meters of fall. Beyond that height, stain diameter no longer increases, so size alone cannot establish fall height.

Impact spatter

A pattern of droplets radiating from a point of impact. Droplet size decreases as the energy of the impact increases, with fine mist associated with gunshot or explosive mechanisms.

Cast-off pattern

A linear trail of elongated stains produced when blood is flung from a moving weapon. Stain size and spacing decrease along the arc as the blood supply is depleted.

Arterial spatter

A gushing, pulsatile pattern with large volume and spine-like projections, produced when a breached artery projects blood. It can indicate the victim's position and movement.

Expirated blood pattern

Fine droplets containing air bubbles and mucus, concentrated near the nose or mouth. It can be mistaken for impact spatter but reflects exhaled air rather than mechanical impact.

Drip pattern

Vertically aligned stains of similar size, often with satellite spatter, produced by blood falling from a stationary source onto a horizontal surface.

Flow pattern

Passive staining that follows surface contours under gravity and pools at low points. It can indicate the orientation of the surface at the time of deposition.

Pooling

Accumulation of blood in a low area, indicating the victim or source remained stationary. The pool shape and flow direction can establish body position and later movement.

Transfer pattern

A stain that records the shape of a contacting object, such as footwear, fabric, or a hand. The pattern can identify the object and its orientation at contact.

Wipe pattern

A smear produced by lateral motion through wet blood on a surface. It alters an existing stain rather than creating a new deposition pattern.

Swipe pattern

A transfer produced when an object bearing blood contacts a clean surface. It differs from a wipe, which involves motion through blood already on a surface.

Void pattern

An absence of blood in an otherwise stained area, marking where an object or person blocked deposition. It can indicate the position of a body, weapon, or furniture during the event.

Satellite spatter

Small droplets surrounding a parent stain, formed when the parent drop breaks up on impact. Satellites are not independent stains for reconstruction purposes.

Skeletonized stain

A stain with a darker rim and lighter center, formed when a later stain overlays an earlier one. It indicates the earlier deposit and helps establish sequence.

Tide mark

A halo at the edge of a dried stain produced by re-wetting, which carries blood outward. Its presence can indicate a second wetting event.

Passive stain

A stain formed under gravity or capillary action, such as a drip, flow, or pool. Passive stains indicate the orientation of the surface and the source's position.

Altered stain

A stain changed after deposition by dilution, absorption, wiping, or removal. Interpretation must account for cleaning, fire, or decomposition at the scene.

Surface texture effect

Rough or porous surfaces increase satellite spatter and distort stain shape, while smooth non-porous surfaces preserve circularity and give the most reliable angle measurements.

Porous surface limitation

Wood, fabric, and concrete absorb blood and distort stain shape. Angle-of-impact calculations on these surfaces are less reliable than on smooth, non-porous targets.

Blood as non-Newtonian fluid

Blood's behavior on impact depends on droplet size, velocity, and surface. Identical mechanisms can therefore yield different stain shapes on different targets.

Impact angle reference values

A width-to-length ratio of 0.5 corresponds to a 30-degree impact; 0.71 corresponds to 45 degrees; 1.0 corresponds to a 90-degree perpendicular impact.

Stain diameter reference

A 0.05 mL blood drop falling about one meter onto a smooth surface yields a stain roughly 10 to 13 mm in diameter. Larger stains suggest greater volume or height.

Minimum stains for origin

At least two stains are needed for a convergence point, but three or more are preferred to assess error and consistency in the origin calculation.

Documentation sequence

Photograph overall, mid-range, and close-up views with a scale and color reference. Record measurements and sketches before any enhancement or collection.

Chemical enhancement caution

Luminol and similar reagents detect latent blood but can dilute DNA and alter stain appearance. Document the untreated scene first and record all reagent applications.

Chain of custody

A documented record of who handled bloodstain evidence at each step. It covers swabs, reference samples, and controls, and gaps can invalidate DNA results.

Pattern analysis versus identification

Pattern analysis reconstructs the mechanics of blood deposition. DNA and serology determine identity; pattern interpretation must not be used to infer individual identity.

Peer review in casework

Independent verification of angle measurements and origin calculations by a second analyst. It reduces error and is standard practice in bloodstain casework and court testimony.

Court testimony limits

Testimony should explain the basis for each conclusion, the limitations of the method, and the distinction between findings that are consistent with a scenario and those that are conclusive.