The Open Door and the Area of Origin
A woman is found assaulted in a living room. On the north wall, 11 elliptical bloodstains are documented, each with a major axis of about 16 mm and a minor axis of about 8 mm; several have tails pointing downward and to the left. A door in the same wall, found open into the hallway, has six similar stains on its hallway-facing side. The door was reportedly closed during the assault and opened by the first responder. The analyst strings the 11 wall stains and obtains a point of convergence; the calculated area of origin is a region about 0.6 m from the wall at a height of 1.3 m. A defense expert argues that the 'void' on the wall in the shape of the door proves the attacker stood in the doorway. The analyst must decide how to treat the door and the void.
1. Calculate the impact angle for the wall stains and explain how the analyst should use that angle when estimating the area of origin.
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The impact angle comes from the ratio of the minor axis to the major axis: sin θ = 8/16 = 0.500, so θ is about 30°. That means the blood struck the wall at roughly 30° relative to the wall surface. The angle is used to project each stain's long axis back into space; the point of convergence is the 2D intersection on the wall, and the area of origin is the 3D region built from those angles. The 0.6 m and 1.3 m values are estimates with a margin of error, not a precise point. The analyst must also confirm that the tails are consistent with the long-axis orientation; if the tails conflict, the angle should not be used. The area of origin describes a region where the event could have occurred, not a fixed body position.
2. How should the door stains and the door-shaped void be treated in the reconstruction?
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The door was reportedly closed at impact, so the six stains on its hallway-facing side may be part of the same spatter event. However, because the door was opened after the event, its current position cannot be used for stringing; the geometry has changed. The 11 wall stains are on a fixed surface and can be used. The door-shaped area on the wall that lacks stains is not a true void caused by a person standing there; it is the shadow of the closed door, which intercepted the spatter. The defense expert's interpretation is therefore unsupported. The analyst should document the door's position at discovery, photograph the door stains, and treat them as a separate, displaced surface. If the door's position at impact can be established, the door stains could be used to test the area of origin, but not by stringing them in their current position.
3. What follow-up would you recommend to test the competing interpretations?
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First, DNA-typing the wall and door stains would show whether they share a source and whether the door stains are relevant. Second, examine the door edge, frame, and handle for transfer or contact stains that could indicate when the door was opened relative to the bloodshed. Third, reconstruct the door's position using the hinge geometry and any floor marks; if the door could not have been closed at impact, the shadow interpretation changes. Fourth, use a laser or stringing method on the wall only, and report the area of origin with an error range. Avoid claiming the void proves a body position. The key is to separate what is fixed from what was moved.