Forensic Science 1-Bloodstain Pattern Analysis-University of Southern Mississippi

What is crime-scene reconstruction?

A method to support a likely sequence of events using physical evidence and involved parties' statements.

Which disciplines typically collaborate on reconstruction?

Medical examiners, criminalists, and law enforcement.

Name two tools/techniques CSIs use for reconstruction.

Trajectory lasers and bloodstain pattern interpretation.

How can a laser help with shooter position?

Aligns victim wound with a bullet hole (e.g., in glass) to define the shooter search area.

Why are bloodstains useful in reconstruction?

Their location, distribution, and appearance encode what happened during a violent event.

List key questions bloodstain interpretation can answer.

Direction of origin, angle of impact, victim position, movement paths, approximate number of blows, and assailant position.

How does surface texture affect stains?

Hard, non-porous → less spatter; rough/porous → irregular edges, serrations, and possible satellite spatter.

What is satellite spatter?

Small droplets distributed around a larger drop from impact with a surface.

How do you read direction of travel from a droplet?

The pointed end/tail faces the direction of travel; disrupted/feathered edge points that way too.

How does shape reflect angle?

90° impact ≈ circular; as angle decreases, stain elongates (longer tail at smaller angles).

What is the formula for impact angle?

sin A = (width / length); A is the angle of impact (use inverse sine). (~±5° error; measure in mm.)

Define impact spatter.

Pattern produced when an object forcefully strikes a blood source, projecting drops outward.

Differentiate forward vs. back spatter.

Forward travels in the same direction as the force; back spatter travels back toward the source.

Low-velocity spatter—drop size & force?

≥4 mm drops; up to ~5 ft/s; minimal force.

Medium-velocity spatter—drop size & force?

~1-4 mm drops; ~5-25 ft/s; often blunt force.

High-velocity spatter—drop size & force?

Caveat about velocity categories?

Useful descriptively; cannot alone specify exact events—use cautiously as investigative tools.

Name three common sources of spatter.

Impact spatter, cast-off spatter, arterial spray.

What is area of convergence?

2D point where elongated stains' axes (tails) intersect—indicates planar origin of drops.

What is area of origin?

3D space where blood was projected from; shows victim/suspect position when created.

Field method to approximate area of origin?

String method using measured angles of impact.

Describe gunshot spatter.

Fine forward spatter from exit wounds; back spatter from entrance wounds (no forward if no exit).

What is the drawback effect?

Back spatter striking the gunman and/or entering the gun muzzle depending on distance.

Define cast-off spatter.

Blood flung in an arc from a bloodied object/weapon between blows onto nearby surfaces.

What affects cast-off features?

Object size/shape, blood volume, and swing direction. Small/pointed → smaller, linear drops; blunt/large → larger, wider pattern.

How estimate minimum number of blows from cast-off?

Count and pair forward/backward arcs; number of arcs + 1 ≈ minimum blows (guideline).

Define arterial spray spatter.

Pattern from injury to a major artery/heart driven by blood pressure; largest spurt marks the injury site; brighter red (oxygenated).

Define expirated blood pattern.

Blood expelled from mouth/nose due to internal injury—often with air bubbles and/or lighter color (saliva dilution).

What is a void pattern?

Blank area where an object/person blocked spatter deposition; can suggest size/shape/position.

Define contact/transfer pattern.

Blooded object touches a clean surface leaving a recognizable shape; simple transfer shows size/shape.

Swipe vs. wipe?

Swipe: bloody object moves across a clean surface. Wipe: clean/moved object goes across a pre-existing bloodstain.

What are flow patterns?

Blood moving under gravity; flow direction can show movement; interruptions suggest sequence/timing.

What is a blood pool?

Accumulation on a level surface; absorbent substrates cause diffusion and apparent enlargement; drying time can inform timing.

What is skeletonization?

Dried rim forms at stain edges (≈50 s for small drops; longer for larger volumes). If disturbed after, rim remains—useful for timing.

What is a drop trail pattern?

Series of separated drops forming a path from a moving, dripping source—can show direction/speed and lead to weapons; collect for DNA.

Practical steps to find area of convergence.

Draw axes/tails through elongated stains on a 2D map/photo; intersection ≈ convergence point.

Practical steps to approximate area of origin.

Measure width/length → angle for multiple drops; project strings/lasers back from stains at those angles to a 3D origin.

Core documentation guidelines for bloodstains.

Note, photograph, and map each pattern; record which stains were sampled.

Grid method—what is it?

Lay a grid of known-size squares over the pattern for scaled photography and mapping.

Perimeter ruler method—what is it?

Place a rectangular ruler frame around the pattern plus a small scale next to individual stains for photos.

Why should all personnel learn BSP basics?

To correctly recognize, record, and preserve patterns for later expert interpretation.

Professional certification mentioned for BSP?

IAI Bloodstain Pattern Certification (BSP).