IAI SP4 common mistakes
IAI SP4 · Understand the traps and how to avoid them.
Photographing a scene or item before placing a scale and evidence/photo identifier in the frame, then trying to add scale information later from notes.
Candidates rush to capture the overall view and treat the scale as a formality, forgetting that an unscaled close-up is often evidentially worthless for later measurement or comparison. Under time pressure the 'document first, scale second' habit carries over from casual photography.
What to do instead
Adopt a fixed shooting sequence for every subject: overall, mid-range, and close-up, with the scale and identifier placed before the shutter release in the mid-range and close-up frames. Practise a mental checklist ('fill the frame, level the camera, place the scale, check the identifier, shoot') until the scale placement precedes the shot by reflex.
Describing a latent print comparison conclusion in absolute identification language ('this is the suspect's print', 'match') rather than using the accepted conclusion scale and stating the basis for the opinion.
Candidates confuse the everyday meaning of 'match' with the disciplined vocabulary of friction ridge examination, and they may not have internalised the conclusion categories (identification, exclusion, inconclusive, no value) or the requirement to articulate the basis.
What to do instead
Memorise the accepted conclusion terminology and the three levels of detail (ridge flow, minutiae, pore/edge/ridge shape). For every answer, state the conclusion category, the level(s) of detail relied on, and the quality/quantity of the comparable area. Practise writing short conclusions that a reviewer could audit without seeing the prints.
Handling biological evidence with wet or damp packaging, or sealing a bloodstained item in an airtight bag before it is thoroughly air-dried.
Candidates focus on 'protect from contamination' and reach for the most secure-looking container, not realising that trapped moisture promotes bacterial degradation and mould that destroy DNA. The drying step is easy to skip when items are collected in a hurry.
What to do instead
Apply the rule: biological items are air-dried at room temperature, then packaged in breathable paper (or rigid container with ventilation) and sealed with tamper-evident tape. Keep a written drying log with time and location. Only package liquid blood in a sterile tube with preservative, and never freeze a damp item.
Breaking the chain of custody by omitting a transfer entry, leaving a time or signature blank, or letting an item pass through an unrecorded courier or temporary storage step.
Candidates treat the form as paperwork to complete at the end rather than a contemporaneous record, and they underestimate how a single gap allows opposing counsel to challenge authenticity and integrity.
What to do instead
Record each transfer at the moment it happens: full name, agency/ID, date and time, purpose, and signature. Use a single continuous form with no blank rows, and if a correction is needed, strike through, initial, and date rather than erasing. Rehearse a full evidence lifecycle (scene to property room to lab to court) and check the form at every handover.
Failing to separate elimination prints and known reference standards from questioned evidence, or collecting known prints without documenting the collection method and consent/authority.
Candidates see elimination prints as a courtesy and known exemplars as trivially available, so they skip the documentation and segregation that keeps the comparison valid and the seizure lawful.
What to do instead
Treat elimination and known prints as evidence: label them distinctly, store them separately from questioned items, document who was printed, when, by whom, and under what authority (consent, warrant, or lawful arrest). Note the inking/scanning method and the quality of the exemplar, and record any refusal.
Answering fingerprint classification questions by pattern name alone (e.g. 'whorl', 'loop') without giving the subclassification, ridge count, or delta/core detail the question is actually testing.
Candidates learn the broad pattern families first and stop there, so they miss that classification asks for specific subtypes (plain whorl, central pocket loop, double loop, accidental; ulnar versus radial loop) and quantified features such as the ridge count between delta and core.
What to do instead
Build a decision tree: is there a delta? how many? does the recurving ridge touch the delta? then assign the subtype and count ridges along the specified path. Practise on clear reference exemplars and always state the subtype plus the supporting features, not just the family name.
Collecting trace evidence with a single swab or taping method regardless of the substrate, contaminating the tool between samples, or losing control samples.
Candidates default to one familiar technique and forget that adhesive tape, swabbing, vacuuming, and picking each suit different surfaces and particle types, and that the absence of a control sample weakens interpretation.
What to do instead
Match method to substrate and analyte: tape lifts for dry particulates on smooth surfaces, damp swabs for biological stains on non-porous items, scraping or vacuum with filters for debris and hair. Change gloves and tools between samples, collect a substrate control from an unstained area, and document the method and area for each sample.
Photographing a scene with on-camera flash at oblique angles and no exposure or colour reference, producing glare, hard shadows, or colour casts that misrepresent the evidence.
Candidates rely on automatic settings and flash because it guarantees a visible image, without considering how flash angle, white balance, and colour reference affect the evidential value of the photograph.
What to do instead
Use a colour and grey reference card in the first frame of each lighting setup, set white balance manually or include a reference for correction, and control lighting deliberately: diffuse or bounce flash, off-camera flash at a low angle for texture, and oblique or alternate light sources for latent prints. Bracket exposures and review the histogram and focus on the camera back before moving on.
Overstating the strength of a forensic association in a report or testimony, or offering opinions outside the examiner's competence and the validated limits of the method.
Candidates conflate 'consistent with' and 'originated from', and they want to give a decisive answer. They may also be unfamiliar with the distinction between the examiner's role and the court's role, and with the duty to disclose limitations and exculpatory findings.
What to do instead
Study the reporting standards for the discipline: state findings, the basis, and the limitations, and avoid source-attribution claims beyond what the method supports. Use calibrated language, disclose alternative explanations, and never opine on guilt, intent, or legal conclusions. Practise peer-reviewing your own draft report against a checklist before release.
Skipping or superficially completing quality-assurance steps: no competency or proficiency test records, no verification of reagents and equipment, no technical review of notes before the report is issued.
Candidates see QA as administrative overhead separate from casework, and under exam conditions they may not connect accreditation requirements (document control, validation, proficiency testing, technical review) to the reliability of the evidence itself.
What to do instead
Learn the QA cycle as part of the case: method validation before use, reagent and instrument checks logged, analyst competency and proficiency records current, contemporaneous notes, and an independent technical review before release. In answers, name the specific control and the record that proves it was done.