The Corrugated Door: Area of Origin on a Curved, Low-Count Surface

Yes, but only as a region, and only after excluding two stains.

Method: for each suitable stain, measure the ellipse length (L) and width (W) and compute the impact angle from sin θ = W/L. The direction of travel lies in the plane containing the long axis and the local surface normal, so each stain yields a trajectory line projected outward at angle θ. Intersecting multiple lines from stains in different locations gives a 3D region.

Problems specific to this door:

• Curvature. Each flute face is only locally planar. The long axis of an ellipse encodes direction relative to the local tangent plane, not the door's overall plane. Treating the whole door as one flat plane puts a systematic error of tens of degrees into lines from valley and crest stains, and the error grows with distance from the surface. The local orientation must be estimated from the flute geometry at each impact point.
• Exclusion of distorted stains. The two crest stains have smeared, irregular margins. Their shapes do not reflect a free-flight droplet, so including them would corrupt the angles. Exclude them from quantitative work and use them only qualitatively (they confirm direction and the event).
• Low count. Nine usable stains across three flutes gives a small number of trajectory lines. Reconstruction quality depends on having several lines from well-separated positions; here the convergence will be broad.
• Consistency check. All nine long axes agreeing on an up-and-left direction is a strong internal validation that the stains are one event, which supports the reconstruction even with a modest count.

Report a volume, not a point, and state which stains were used and which were excluded.

I would decline the single dot and explain why, in terms the detective and prosecutor can use.

Reasons the dot is unsupportable:

1. Every measurement carries uncertainty. Ellipse width is read to the nearest 0.1 mm; at small impact angles, a tiny width error produces a large angular error.
2. The impact angle describes the droplet's path only at the instant of contact with the local surface. On a curved door, the local plane must itself be estimated, adding another error term.
3. Nine stains produce far fewer independent convergence checks than a typical reconstruction; the confidence region on curved geometry with a small count is large.
4. Blood droplets are not infinitely small points, so each trajectory is a cone, not a line.
5. A reconstructed origin is a location in space where blood was travelling from. It is not the position of a person, a weapon, or a body part, and it does not identify who was there.

What I report instead:

• The method, software (if used), minimum stain criteria, and the exact stains included and excluded.
• A three-dimensional region, with dimensions and the software's confidence settings stated explicitly.
• The principal error sources, ranked, and a statement of how the region would change if the curved geometry were approximated as flat.
• A plain statement that the region is consistent with a source in a given area of the garage, and that the body position should be evaluated separately against it.

Framing the answer as 'here is what the data can and cannot support' is more defensible on the stand than any dot, and it protects the conclusion from a challenge that the analyst manufactured precision.

The two crest stains:

• Photograph them first, in place, with a scale and oblique lighting, and record their exact position relative to the flute geometry, including which way the smearing runs.
• Document them as distorted and classify their shape quality plainly. A smear indicates the droplet struck an edge or was dragged; this is information about the geometry, not noise to be discarded silently.
• Exclude them from measurement. Averaging a smear into an ellipse fit is one of the more common ways a reconstruction gets quietly wrong.
• Use them qualitatively: if their general direction agrees with the nine measurable stains, say so and note that this supports a single event.

The door:

• Record the door's real-world orientation before anything moves: plumb, level, height of each stain cluster above the floor, and the direction the door faces. Trajectories are only meaningful relative to a documented reference frame.
• Photograph the whole door square-on with a scale, then close-ups with scale and a plumb reference.
• If the door must be removed, coordinate with the scene and photograph the removal so the orientation record survives. Removal changes the physical reference, and a later examiner cannot recover it.
• Do not clean or treat the surface. Note any rust, oil, or condensation that could be mistaken for blood and flag it for presumptive and confirmatory testing.

If destructive sampling is requested, take substrate controls from adjacent unstained flutes and document exactly where each sample came from.