IAI SP5 common mistakes
IAI SP5 · Understand the traps and how to avoid them.
Treating every spatter pattern as impact spatter and classifying it by droplet size alone, without first deciding whether the mechanism is impact, expiration, cast-off, or projection.
Droplet size is the most visually obvious feature, so candidates jump straight to a size table and skip the mechanism-based classification step that the pattern actually requires.
What to do instead
Before assigning any category, document the whole pattern: directionality, distribution, volume, and relationship to the source. State the mechanism first, then use size and velocity as supporting descriptors. Practise with mixed-mechanism scenes where size alone is misleading.
Reading bloodstain direction of travel from the pointed end of a single stain without accounting for the surface angle and the difference between the stain's long axis and its direction of travel.
Textbook diagrams show an ideal ellipse on a flat, non-absorbent surface; real stains on textured, angled, or absorbent substrates distort, and candidates apply the rule mechanically.
What to do instead
Work through angle-of-impact and directionality problems on tilted and porous surfaces. Always record the substrate and its orientation, and note when a stain is too distorted to support a direction call rather than forcing one.
Documenting a scene by photographing only the items of evidence and not establishing overall, mid-range, and close-up coverage with a scale and a consistent reference point.
Candidates treat photography as a record of objects rather than a record of spatial relationships, and time pressure pushes them toward the most obviously relevant items.
What to do instead
Use a fixed three-tier sequence (overall, mid-range, close-up) for every scene and every item, with and without a scale. Build the habit of shooting the transition shots that link one tier to the next so a reviewer can walk the scene from the images alone.
Failing to establish and maintain the chain of custody and contemporaneous scene notes, reconstructing details later from memory.
The technical work feels like the real job, and documentation is seen as administrative overhead; candidates underestimate how much a defence challenge will focus on continuity and timing.
What to do instead
Write notes at the point of collection, recording time, location, collector, packaging, and seals. Practise timed exercises where notes are graded as strictly as the evidence handling, and rehearse explaining continuity gaps honestly instead of papering over them.
Making an identification or exclusion from footwear outsole impressions based on pattern similarity alone, without assessing wear, damage, and the individual characteristics needed to support that conclusion.
Class characteristics are easy to see and produce a satisfying match; individualising features require slower comparison and an understanding of the limits of the evidence.
What to do instead
Separate the conclusion into class-level (make/model/size) and individual-level, and state which level the evidence supports. Practise comparisons using known prints with heavy wear and damage, and write conclusions that explicitly state the basis and the limitations.
Photographing footwear and tire impressions without the correct lighting angle and scale, producing images that cannot support comparison.
Candidates rely on ambient light and standard flash, which flattens two- and three-dimensional impression detail and obscures fine tread edges.
What to do instead
Use oblique lighting for two-dimensional impressions and adjust angle to reveal edge detail; place an L-shaped or linear scale in the same plane as the impression. Re-shoot if the tread edges are not crisp, and learn to judge image adequacy before leaving the scene.
Attempting facial comparison or age progression without documenting the limits of the method and the quality of the source images.
Forensic art tasks invite confident visual judgements, and candidates present a conclusion without discussing image resolution, pose, illumination, or the assumptions built into an age progression.
What to do instead
Always pair the product with a statement of source quality, method, and limitations, and avoid expressing identification certainty from imagery alone. Practise writing caveats that are specific to the images used rather than generic disclaimers.
Enhancing images (sharpening, contrast, resampling, or filtering) and presenting the result as if it were the original evidence, without preserving and documenting the unaltered source.
Enhancement makes images look clearer and more evidential, and the processing steps are easy to forget once the output looks good.
What to do instead
Preserve the original file with a hash, perform all processing on working copies, and log every step with parameters so the result is reproducible. Present enhanced and original side by side and state clearly what was changed and why.
Comparing latent prints to known prints by scanning for a few matching ridge features and stopping once a match is found, without an ACE-V-style disciplined sequence or documentation of the analysis and comparison stages.
Once a candidate sees a plausible correspondence, confirmation bias drives the rest of the comparison, and the analysis stage that should define what is usable in the latent gets skipped.
What to do instead
Work the sequence explicitly: analyse and document the latent's clarity, distortion, and usable area before looking at the known; compare; evaluate; verify independently. Practise on non-matching latents to build the discipline of stopping and reporting inconclusive or exclusion.
Confusing tenprint classification and search decisions with the identification decision itself, and mishandling marginal or poor-quality tenprint cards.
Tenprint work is often taught as a classification exercise, so candidates treat a classification code or a candidate list as the answer and under-attend to print quality, finger identification, and the verification step.
What to do instead
Separate the tasks: classification and searching produce candidates; verification against the actual impressions produces the identification. Practise with smudged, rolled, and mislabelled cards, and always confirm finger position and print quality before submitting or concluding.