IAI SP9 cheat sheet

Impact spatter: stains radiate outward and backward from a point of origin; directionality is read from the long axis of each elliptical stain pointing toward the impact surface.

Angle of impact: sin θ = width / length of the stain; measure the minor and major axes of a well-formed single droplet stain.

Area of origin: draw lines through the long axes of several stains back to a point of convergence, then calculate height z = d × tan θ for each stain (d = horizontal distance to convergence).

Low-velocity spatter: droplets typically 4 mm or larger, produced by gravity drip or low-energy impact; high-velocity spatter: droplets generally under 1 mm from gunshot or explosive force.

Cast-off: linear trail of stains of decreasing size along the arc of a swinging weapon; each swing produces a separate trail.

Arterial spatter: repetitive, gushing pattern with satellite stains and a wave-like appearance, reflecting the heartbeat.

Expirated blood: fine mist with air bubbles and possible mucous strands, often on surfaces near the victim's mouth or nose.

Void patterns: absence of staining where an object or person blocked deposition; used to infer position or later movement of an item.

Transfer and contact stains preserve the shape of the contacting object; direction of transfer is determined from the object's geometry and the stain's edge characteristics.

Sequence of scene processing: secure and preserve, document (notes, photos, sketch), search, collect and package, then release; documentation precedes collection.

Chain of custody: every transfer of evidence records item number, description, collector, date/time, and receiving party; a break in the chain affects admissibility.

Search patterns: line/strip for large open areas, grid for thorough coverage, spiral (inward or outward) for confined spaces, zone for irregular or multi-room scenes, wheel for a focal point.

Rough sketch records measurements, orientation, and fixed reference points; the final or scale diagram is drawn later from notes and measurements.

Wet or biological evidence is air-dried before packaging; each item is packaged separately to prevent cross-contamination.

Paper packaging is used for biological and arson evidence; airtight plastic is avoided for damp items and for accelerant residues.

Locard's exchange principle: every contact leaves a trace; the scene is treated as a source of transfer evidence.

Control samples (substrate, reference, or blank) accompany questioned samples to interpret analytical results.

Three-level identification: class characteristics (manufacturer, model, size), design characteristics (wear, damage), and individual characteristics (random cuts, nicks, embedded objects).

Tread design comparison requires test impressions from a known shoe of the same make and model; design alone cannot individualize.

Photograph footwear impressions with a scale and at 90° to the surface; oblique lighting reveals surface detail.

Impression recovery: electrostatic lifting for dry dust impressions on hard surfaces; gelatin or adhesive lifts for residue on porous or textured surfaces.

Casting with dental stone or plaster is used for impressions in soil, snow, or sand; a soil sample and photographs accompany the cast.

Tire track comparison uses tread width, circumference, track width, and design elements; wear and irregular damage can individualize a tire.

Impressions in blood or on skin require specialized photography and may be enhanced with chemical or lighting techniques rather than lifting.

Shoe size is recorded as length and width in the manufacturer's system; size alone is a class characteristic and cannot identify a wearer.

Facial reconstruction: build tissue-depth markers along standard landmarks (glabella, nasion, mid-pharyngeal, mental eminence) using population-specific depth tables.

Two-dimensional composite methods: feature-by-feature selection (e.g., facial identification catalog systems) and sketch-based drawing from witness description.

Cognitive interview techniques reduce suggestion: use open-ended prompts, avoid leading questions, and record the witness's own words.

Age progression relies on documented growth patterns of the skull and soft tissue; the cranium is largely adult-sized by late adolescence.

Postmortem identification artwork includes reconstructions from skeletal remains and image enhancement of unidentified decedents.

Standard reference planes: Frankfort horizontal plane and the nasion–mental eminence relationship guide profile reconstruction.

Composites are investigative leads, not positive identification; they are released with the caveat that features may vary.

Photograph the scene in three scales: overall (wide), mid-range (evidence in context), and close-up (detail with a scale).

Always include a scale in close-up evidence photographs; the scale is placed in the same plane as the evidence.

Exposure triangle: aperture controls depth of field, shutter speed controls motion blur, ISO controls sensor sensitivity and noise.

Alternate light sources: oblique lighting for texture, ring or coaxial lighting for flat surfaces, UV/IR for latent or altered evidence.

Forced perspective and parallax are avoided by keeping the camera sensor parallel to the evidence plane.

Photogrammetry and 3D scanning record geometry; calibration targets are needed to correct lens distortion.

Digital image integrity: preserve the original file, document any enhancement, and maintain an audit trail of processing steps.

Filters: a polarizing filter reduces glare on non-metallic surfaces; a barrier filter is used with fluorescent techniques.

DVR/NVR exports should include the native file and player; re-encoding or screen capture degrades evidence and should be documented.

Time offset between video and the known incident time is established from a reference event and recorded as a correction factor.

Frame rate and interlace: fields within a frame may show different moments; deinterlacing choices affect measurement.

Height estimation from video uses the pinhole camera model and a reference of known height in the same plane as the subject.

Pixel aspect ratio and lens distortion must be corrected before any measurement; calibration uses known reference objects.

Authentication of video considers metadata, hash values, and continuity of the recording; the chain of custody applies to digital files.

Enhancement (brightness, contrast, stabilization) is documented step by step; enhancement cannot add information absent from the original.

Latent print development sequence: visualize, preserve, then compare; the least destructive technique is applied first.

Porous surfaces: ninhydrin, DFO, and physical developer for amino acid and lipid components; sequence matters.

Non-porous surfaces: cyanoacrylate fuming, then powder or dye stain; fluorescent dyes and laser/ALS enhance developed prints.

Blood-contaminated prints: use protein stains (e.g., amido black, acid yellow) rather than amino acid reagents.

ACE-V: Analysis, Comparison, Evaluation, Verification; verification is an independent examination by another qualified examiner.

Levels of detail: Level 1 (ridge flow and pattern), Level 2 (minutiae or ridge path), Level 3 (pores, ridge width, edge shape).

Sufficiency determination is made at the Analysis stage; a print with insufficient detail is not compared to a known.

Documentation includes photographs of the print in situ with a scale before lifting, and the lift or developed item is preserved.

Henry classification: values assigned to fingers (1 for whorls on even fingers, 2 for whorls on odd fingers) with primary ratio and secondary/other keys.

Pattern types: arch (plain, tented), loop (ulnar, radial), whorl (plain, central pocket, double loop, accidental); loops require a delta and one ridge count.

Ridge counting is performed along a straight line from the delta to the core; the count excludes the delta and the core.

Classification values: arch = 0, tented arch = 0, loop (ulnar or radial) = 1, whorl = 2 in most tenprint classification schemes.

Tenprint cards record all ten fingers with rolled impressions and plain impressions; plain impressions verify the rolls.

AFIS/NGI searches use pattern classification and minutiae; candidate lists are then examined by a qualified latent print examiner.

Ridgeology: ridge flow, ridge path, and third-level detail support the conclusion; no fixed numerical standard is used in the ACE-V framework.