IAI SP4 cheat sheet

Scene documentation proceeds in a fixed order: initial assessment and scene security, then photography before any movement, then sketches with measurements, then detailed notes, then collection; each later step must be traceable to the earlier record.

Sketch types: rough sketch (first working drawing at scene), finished scale diagram (drawn to scale from rough sketch and measurements), and exploded or perspective view used to show vertical relationships and overlapping planes.

Rectangular coordinate method locates an item by two perpendicular distances from fixed reference lines; triangulation uses distances from two known fixed points to the item; baseline method measures offsets from a single established line.

A datum point is a fixed, permanent reference (e.g., a wall corner or utility mark) from which all measurements are taken; every sketch must state the datum, the measurement units, and the compass orientation.

Chain-of-scene control: an entry/exit log records name, agency, time in, time out, and purpose for every person; the log is a legal record and must be preserved with the case file.

First responder priorities in order: render aid and secure safety, secure and preserve the scene, detain witnesses and suspects, then record and release to the investigator; scene alteration before documentation must be noted in the report.

Locard's exchange principle: every contact leaves a trace; it justifies systematic collection of both the obvious items and the contact surfaces between suspect, victim, and scene.

Scene search patterns: line/strip (outdoor large areas), grid (double line, thorough), spiral (circular or inward/outward), zone/quadrant (large or multi-room), and wheel/ray (small central-point scenes).

Notes must be contemporaneous and include date, time, location, weather, lighting, personnel, observations, and any deviations from standard procedure; corrections are made with a single line and initials, never erasure.

Three photographic stages: overall (establishing the scene and its context), mid-range (item in its surroundings), and close-up (detail with a scale); each close-up should be preceded by a mid-range frame that shows where the item was.

A scale must be placed in the same plane as the evidence and photographed so that it is level and unobstructed; an angled or elevated scale introduces perspective error and undermines later measurement.

For a given exposure, depth of field increases with smaller aperture (higher f-number) and with shorter focal length, and decreases with closer subject distance; close-up work therefore needs small apertures and adequate light.

Reciprocity: exposure is the product of intensity and time; halving aperture area (one stop) requires doubling shutter time, and each full stop is a factor of two in light.

Perspective distortion is controlled by keeping the film/sensor plane parallel to the subject plane; a camera tilted upward converges vertical lines, which is unacceptable for scale photographs of impressions.

Oblique lighting (light raked at a low angle) reveals surface texture and indented writing; axial or coaxial lighting is used for reflective surfaces and for flat, high-contrast impressions.

Alternate light sources: UV (reflected or fluorescent) for body fluids, fibers, and some treatments; infrared for dark or bloody substrates and charred documents; lasers and forensic light sources with barrier filters for latent prints.

Photographic documentation must be original and unedited; any enhancement (contrast, cropping, sharpening) is documented and applied to a copy, with the original preserved and hash-verified for authenticity.

Photogrammetry derives measurements from photographs taken with a known scale and camera position; it requires calibration data and is admissible only when the method and error margins are documented.

Latent print development sequence: visual/non-destructive examination first, then powder or cyanoacrylate fuming on non-porous surfaces, then chemical methods (ninhydrin, DFO, physical developer) on porous surfaces; the order matters because some methods destroy others.

Powders (black, bichromatic, magnetic) work on smooth non-porous surfaces; cyanoacrylate fuming polymerizes on the print residue and is followed by a dye stain (e.g., rhodamine, basic yellow) for contrast.

Ninhydrin reacts with amino acids and is used on porous surfaces such as paper and cardboard; heat and humidity accelerate the reaction; DFO is a related amino-acid reagent that fluoresces under laser/ALS.

Physical developer detects prints on porous surfaces after wet or previously wetted conditions, including paper that has been soaked; it is used after ninhydrin because it detects lipid/other components.

Impression evidence: footwear and tire impressions are documented with photographs including a scale, then cast with dental stone or electrostatic lifting for dry residue; comparisons use class characteristics plus randomly acquired individual characteristics.

ACE-V: Analysis (assess the print's clarity, distortion, and features), Comparison (side-by-side, then overlay), Evaluation (determine identification, exclusion, or inconclusive), and Verification (independent second examiner review).

Ridgeology: the study of friction ridge formation and the uniqueness and persistence of ridge detail; identification requires agreement of ridge flow, ridge characteristics (minutiae), and pore/edge detail in sufficient quantity and quality.

Levels of detail: Level 1 (ridge flow and pattern type), Level 2 (minutiae: ridge endings, bifurcations, dots, islands, spurs), Level 3 (pores, ridge width, edge shape, incipient ridges).

Contamination control for latent prints: change gloves between items, avoid touching the print area, package each item separately, and never process or handle prints before photographic documentation.

Chain of custody is a chronological record of every transfer: item number, description, collector, date/time, location, recipient, and purpose; a break in the chain can render evidence inadmissible or reduce its weight.

Package each item separately; never commingle items from different locations or different suspects, because cross-contamination destroys the evidentiary value of trace and biological material.

Paper packaging (envelopes, bags) is used for biological and moist items so they can dry and breathe; plastic bags trap moisture and promote mold and degradation, so they are used only for dry, non-biological items.

Wet or bloodstained items are air-dried before packaging; if they cannot be dried, they are packaged in paper with a warning label and transported promptly to a controlled drying facility.

Sharps (needles, blades, broken glass) go into rigid puncture-resistant containers; firearms are unloaded if safely possible, secured with the action open, and packaged in a rigid container with the muzzle protected.

Seals: each package is sealed with evidence tape across the opening, and the sealer writes initials, date, and time across the seal so that any opening is visible; resealing requires a new seal and a note in the record.

Latent print lifts and swabs are packaged flat and not folded; swabs are air-dried before packaging and stored cold where the protocol requires it.

Hazardous or controlled substances must be documented, weighed, and packaged per agency and legal requirements; the weigh-in and any field test are recorded with the item number.

Documentation of the item includes its exact location, condition, and any apparent alterations; the item number on the package must match the item number in the notes, sketch, and photographs.

Universal precautions: treat all biological material as infectious; wear gloves, eye protection, and a mask where aerosols are possible, and change gloves between items and after contact with any surface.

DNA is degraded by heat, moisture, sunlight, and time; biological evidence is dried, kept at cool temperatures (refrigerated or frozen per protocol), and never stored in plastic or in a hot vehicle.

Bloodstain pattern categories: passive (drops, flows, pools), spatter (impact, cast-off, arterial, expiration), and altered (voids, transfers, saturation); documentation precedes any interpretation.

Impact spatter analysis uses the angle of impact from the ellipse: sin θ = width / length; the point of origin is estimated by back-projecting the long axes of several stains.

Trace evidence includes hair, fiber, glass, paint, soil, and gunshot residue; collection uses tape lifts, forceps, or vacuuming with a clean filter, and control samples from the scene are collected alongside the questioned sample.

Hair: the root sheath indicates whether hair was pulled (follicular tissue) or shed (telogen); hair comparison is class evidence, while nuclear DNA from the root can be individualizing.

Reference and control samples (victim, suspect, scene) are essential; a questioned sample without a control cannot be compared, and controls must be collected and packaged separately.

Gunshot residue collection uses adhesive stubs on the hands and is time-sensitive; the sample must be labeled with the time collected and the person's activities since the event.

Sexual assault evidence: the kit is collected by a trained examiner, each swab and smear is labeled with the body site, and the kit is sealed and refrigerated; the victim's clothing is collected separately in paper.

Henry classification: primary classification uses the presence of whorls in each of the ten fingers, with the fingers paired (1&2, 3&4, 5&6, 7&8, 9&10) and a fraction formed from the sums of whorl-bearing pairs; the value is expressed as a fraction or ratio.

Pattern types: arches (plain, tented), loops (ulnar and radial, with ridge count), and whorls (plain, central pocket, double loop, accidental); the loop count is taken along a straight line from the delta to the core.

A loop must have one delta and one core; a whorl must have two deltas; an arch has no delta; a tented arch has a ridge that rises to a point or angle.

Minutiae types: ridge ending, bifurcation, dot/island, short ridge, spur, bridge, enclosure, and crossover; a comparison weighs the type, position, direction, and relationship of each.

The comparison process: analyze the unknown for clarity and distortion, analyze the known, compare feature by feature, evaluate in context, and verify independently; conclusions are identification, exclusion, or inconclusive, never a probability of identity.

Distortion sources include pressure, slippage, substrate curvature, and the deposition medium; distorted prints may be compared but the distortion must be explained, not ignored.

AFIS/NGI: the tenprint database is searched by classification and feature vectors; a candidate list is returned and every candidate must be visually compared and verified by a qualified examiner; an AFIS hit is not an identification.

Palm prints and partial prints are compared using the same ACE-V framework; the palm's larger area provides more ridge detail, and the thenar/hypothenar areas must be oriented correctly.

Daubert factors for admissibility: testability, peer review and publication, known or potential error rate, standards controlling the technique, and general acceptance; the judge decides admissibility, the jury decides weight.

Frye standard (where used) requires the technique to be generally accepted in the relevant scientific community; the federal and many state courts apply Daubert or a hybrid standard.

The CSI effect: jurors may expect scientific evidence in every case; examiners must not overstate conclusions and must explain limitations in plain language.

Chain of custody and documentation are the primary targets of cross-examination; contemporaneous notes, sealed packages, and complete logs are the best defense against a challenge.

Bias control: examiners should be blind to case context where feasible, use linear sequential unmasking, and document any exposure to contextual information; verification must be independent of the original examiner.

Accreditation and standards: ISO/IEC 17025 and 17020 for laboratory and inspection bodies, the OSAC and NIST standards for forensic methods, and ASCLD/LAB or ANAB accreditation; proficiency testing and audits are required.

Discovery obligations: the examiner's notes, bench notes, photographs, and any exculpatory findings must be preserved and disclosed; destroying or failing to disclose such material is an ethical and legal violation.

Testimony ethics: state qualifications truthfully, distinguish observation from interpretation, concede the limits of the method, and do not testify beyond the scope of the analysis performed.

Error management: document deviations from protocol, conduct root-cause analysis, and apply corrective action; a known error must be disclosed to the court and the affected parties.