ACSP exam 2

What can BPA help us determine

• Direction and angle of travel of droplets.

• Area of origin and point of convergence.

• Force type and number of blows or impacts.

• Relative positions of individuals and objects.

Pasive stains

drops, pools, flows

gravity driven stains that may clot or show serum separation

Transfer

swipe, wipe and pattern transfers

contact between surface and source

projected/impact

cast-off, arterial, expiratory

formed by external force, indicate directionality

Miscellaneous

fly spots, skelotonized voids

irregular or secondary pattern types

Impact angle formula and what stains to look for

: Θ = sin⁻¹(width/length). Elliptical stains provide more accurate directionality than circular stains.

Documentation of blood stains

• Notes: Describe appearance, size, and location of stains.

• Sketches: Cross-projection to show vertical and horizontal relationships.

• Photography: Overall, mid-range, and macro close-ups with L-scale.

• Roadmapping: Label each pattern alphabetically (A, B, C) and individual stains numerically (A-1, A-2). • Scale Placement: Align parallel to the stain’s long axis.

• Collection: • Swab representative stains for DNA testing.

• Target patterns of most evidentiary value. • Collect known buccal swabs for comparison.

What type of stains are to be prioritized when documenting

Symmetrical stains

Select stains that are clearly isolated and formed on smooth, non-absorbent surfaces. Circular stains (≈ 90° impact) provide less directional information than elliptical ones.

directionality and point of convergence

Directionality is determined by the tail of the stain, which points in the direction of travel. Measure along the major axis of each stain, ensuring photographic scales are aligned parallel to that axis for accuracy.

The point of convergence represents the intersection where trajectories from multiple elliptical stains meet. This combined with the angles of impact can demonstrate approximate origin of a blood event.

Internal ballistics

Fire arm examiner

analyze firearms and ammunition

external ballistics

CSI

Projectile trajectory once fired

Terminal ballistics

Pathologist

interaction with human body

Shooting documentation

• Firearm and ammunition placement'

• Spent casings, bullet defects, and trajectories

• Gunshot residue and bloodstain correlation

• Wounds and impact surfaces

• Witness statements and corroborating evidence

Bullet defect documentation

• Measure defect dimensions, height from floor, and distance from fixed points.

• Use trajectory rods, center guides, plumb bob, protractors, and strings/lasers for perforating defects through two planes with a straight trajectory.

• Use angle impact equation for other defects, though lots of error.

Surfaces effected by a bullet

• Frangible surfaces (e.g., concrete) tend to crumble and produce smaller or fragmented defects.

• Non-frangible surfaces (e.g., sheet metal) stretch or tear, creating larger or irregular defects.

Glass and bullets

o Sequence of shots – radial fractures from subsequent shots will terminate at the radial fractures of the first shot (glass)

o Direction of force – beveling/coning present on exit side (glass)

o Direction of force – 3R Rule: Radial fractures form a Right angle on the Reverse side of force.

o Tempered glass forms a mosaic pattern with irregular subsequence shots devoid of concentric or radial fractures.

Fire scenes

Objectives: Determine the origin and cause of the fire using systematic scene documentation and evidence collection.

Fire causes

Accidental: unintentional ignition via machine failure, short circuit or other factors.

Natural: acts of god such as lighting

Incendiary: deliberate acts of arson

Undetermined: insufficient data

Fire Documentaion

• Methodology: exterior to interior, least to most damage.

• Document fire and soot patters (ex: 'V' patterns, clean burn areas, and direction of f lame movement.)

• Record possible ignition sources, melted materials, and accelerant indicators.

• Multiple areas of origin suggest incendiary fire.

• Handle human remains carefully; pugilistic pose results from heat contraction.

• Collect samples in unlined paint cans or nylon bags. Avoid plastic containers.

Underwater scene processing

Circle: expanding radius from fixed point used for isolated objects

Arc pendulum: Diver sweeps back and forth around a fixed point

Jackstay: Two divers move along a measured line for grid-like coverage; most thorough.

Snag-line: Weighted line drags across area to snag large items quickly.

Underwater documentation

• Mark items with buoys or tie-downs; prepare surface and underwater sketches.

• Photograph with scale references—consider 33% magnification underwater.

• Understand light complications – reduced light, murkiness, more blue/green wavelengths at greater depths.

• Recover bodies or evidence in bags underwater to prevent evidence loss.

• Understand five phases of motion of bodies: settling, bottom movement, ascent, surface drift, final descent.