Cast-Off
Definition
Blood thrown off a swung object (a hammer, a knife, a bat). The trail records the arc of the swing and often the number of blows minus one.
- Cause
- Blood thrown off a swung object
- Typical weapons
- Hammer, knife, bat
- Records
- Arc of the swing
- Blow count clue
- Number of cast-off trails often equals blows minus one
Common questions
Why does the number of cast-off trails tend to be one less than the number of blows?+
The first blow strikes a source with no blood yet on the weapon, so it produces no cast-off, while each subsequent swing flings blood already on the weapon from the prior impact, giving one fewer visible trail than the total blow count.
What can the arc of a cast-off pattern tell an analyst about the scene?+
The trail's curve and the spacing of drops indicate the swing's plane and direction, helping reconstruct the assailant's position and arm motion relative to the victim, and whether the attack involved one arm consistently or a change in stance.
Related terms
- Area of Convergence
- The 2-D point on a surface where the projected trajectories of multiple impact stains intersect. It's the floor-projection of the impact source.
- Area of Origin
- The 3-D point in space where the blood-shedding event occurred, derived from the area of convergence plus the angle of impact for...
- Non-Newtonian Fluid
- A fluid whose viscosity changes with the shear rate. Blood thins under fast shear (a fast swing of a weapon) and thickens...
- Parent Stain
- The primary drop that produces a drip pattern. The smaller surrounding spatters are the satellite spatter; together they tell you about drop...
- Surface Tension
- The cohesive force at a liquid's surface that lets a drop hold a spherical shape in flight. Whole blood sits around 58...