IAI SP9 common mistakes
IAI SP9 · Understand the traps and how to avoid them.
Treating every bloodstain as a passive drip or gravity-driven pattern and classifying spatter by the stain shape alone, without first reconstructing the impact angle and point of origin.
Candidates memorize pattern names from textbook diagrams and then pattern-match on individual stain silhouettes, but IAI bloodstain items usually present a described scene where directionality, angle of impact, and convergence/stringing must be computed before a label is defensible.
What to do instead
For each described stain set, explicitly compute the angle of impact from width/length ratio (sin θ = W/L), determine direction of travel from the tapered end and satellite distribution, and converge the long axes to a point or area of origin before selecting a pattern term. Practice with worked numeric examples until the sequence is automatic.
Confusing the classification thresholds between low-, medium-, and high-velocity impact spatter and applying velocity categories to mechanisms that are not impact (e.g., expiration, cast-off, arterial).
Older training materials still use velocity terminology with loosely stated ranges, and candidates apply a single stain diameter cutoff to every case rather than recognizing that mechanism and stain-size distribution must be assessed together.
What to do instead
Learn the mechanism-based categories (impact, cast-off, arterial, expiration, transfer, flow, drip, void) and the stain-size ranges conventionally associated with each, then drill items where the same stain size appears in two different mechanisms so you must use context, distribution, and scene geometry to choose.
Describing crime scene documentation as a checklist of 'photograph, sketch, collect' without sequencing the steps, establishing the scene perimeter and entry/exit control, or explaining how documentation supports later reconstruction and court presentation.
Candidates study documentation as a list of tasks rather than a defensible process, so they omit initial walk-through, scene security log, baseline/overall/mid-range/close-up photo sequence, and the chain-of-custody link to the sketch and report.
What to do instead
Build a fixed narrative template: secure and log, initial walk-through, overall then mid-range then close-up photography with scale, sketch with measurements tied to fixed reference points, evidence collection with packaging and chain-of-custody entries, and final scene condition. Rehearse the template against hypothetical scenes until the order is automatic.
Overstating footwear conclusions, e.g., asserting a specific shoe made a questioned impression from class characteristics alone, or ignoring the possibility of multiple shoes sharing the same outsole design.
Candidates conflate 'consistent with' with 'identification' and do not separate class characteristics (size, tread pattern, general design) from individual characteristics (wear, damage, acquired defects), which is exactly where footwear items test judgment.
What to do instead
Practice writing conclusions in the graded language of the discipline (identified, very strong, strong, moderate, limited, excluded, inconclusive) and always state which features support the level. For each practice item, list what would be needed to move from class to individual association.
Treating footwear impression recovery as a single technique, rather than matching the recovery method to the substrate (e.g., electrostatic lifting for dry dust on hard surfaces, gelatin or casting for three-dimensional impressions in soil or snow).
Candidates learn one or two lifting methods and apply them universally, missing that substrate, moisture, and impression type dictate the appropriate enhancement and recovery sequence.
What to do instead
Create a substrate-to-method matrix (dry residue on tile, blood on fabric, impression in mud, impression in snow, impression in dust) and for each entry state the enhancement, lifting or casting method, and the reason. Test yourself by covering the matrix and reconstructing it from memory.
Approaching forensic art items as pure drawing skill and ignoring the procedural constraints, such as avoiding leading suggestions during a composite interview and documenting the witness's own descriptors before any image is produced.
Candidates underestimate the cognitive-interview and bias-avoidance content of forensic art and answer on aesthetics or software features instead of on how the image is elicited and validated.
What to do instead
Study the composite process as a protocol: pre-interview instructions, open-ended recall, feature-by-feature elicitation, neutral prompting, iterative review with the witness, and documentation of revisions. Practice identifying leading or contaminating questions in sample interview transcripts.
Answering forensic photography items on camera settings alone while ignoring the requirements for evidentiary validity: scale placement, perspective and distortion control, lighting consistency, and the need for overall-to-close-up coverage.
Candidates equate good photographs with technically exposed photographs and forget that an image must be reproducible in scale and free of avoidable distortion to be useful for comparison and court.
What to do instead
For every photography item, check four things explicitly: is a scale present and in the same plane as the subject, is the camera axis perpendicular to the subject plane, is lighting even and documented, and is the image part of a complete overall/mid-range/close-up series. Learn the specific distortion effects of oblique angles and short focal lengths.
Treating forensic video as frame-by-frame viewing and offering an identification or measurement from an enhanced or upscaled image without addressing original-file preservation, frame rate, compression artifacts, or the limits of enhancement.
Candidates are drawn to the visual output of enhancement tools and do not appreciate that upscaling cannot create detail, that compression and interlacing introduce artifacts, and that the original must be preserved and hashed before any processing.
What to do instead
Study the workflow in order: acquire and hash the original, work only on copies, document every processing step, and distinguish enhancement (contrast, stabilization, frame averaging) from interpolation that invents pixels. Practice stating, for a given described clip, what can and cannot legitimately be concluded.
Confusing the levels of latent print conclusion and the criteria behind them, e.g., calling a comparison 'identified' on quantity of matching ridge features alone without assessing clarity, distortion, and the sufficiency of the latent.
Candidates memorize a numeric feature threshold and apply it mechanically, but modern latent print reporting requires evaluating the quality and clarity of the latent and the rarity of the features, not just counting minutiae.
What to do instead
Practice using the graded conclusion scale (identification, exclusion, inconclusive, no value) and, for each practice comparison, write a short justification citing clarity, distortion, pressure, substrate, and specific corresponding features. Learn to articulate why a low-clarity latent with many features may still be of no comparison value.
Mixing tenprint and latent print concepts, such as applying tenprint rolling and classification rules to latent comparisons, or misapplying Henry classification and ridge-count rules in tenprint items.
The two domains share vocabulary but differ in purpose, quality expectations, and procedure, and candidates who study them together blur the boundaries under exam pressure.
What to do instead
Build a side-by-side comparison of tenprint versus latent work covering purpose, capture method, quality requirements, classification use, and reporting language. Drill tenprint-specific skills separately: pattern interpretation, ridge counting and tracing, and correct application of the classification formula.