IAI SP5 cheat sheet

Impact spatter: stains are small (typically <4 mm), numerous, and radiate from a point of convergence; directionality follows the long axis of individual stains.

Passive drops falling vertically produce circular stains on horizontal surfaces; an elliptical stain indicates an angled impact, and the ellipse's minor-to-major axis ratio approximates the sine of the impact angle.

Angle of impact formula: sin θ = width / length of the stain; measure the ellipse's minor axis (width) and major axis (length).

Point of origin in 3D is found by stringing or computing lines from individual stains at their impact angles back through the point of convergence.

Arterial spatter shows a repeating, gushing pattern with varying stain sizes along a projected arc, reflecting the heartbeat rhythm.

Expirated blood appears as fine mist mixed with air bubbles and mucus, often near the nose/mouth of a victim.

Cast-off patterns form linear trails of stains; the number of stains and spacing can indicate the number of swings and the weapon's arc.

Void patterns (absence of blood where surrounding areas are stained) can indicate an object or person was present at the time of bloodshed.

Transfer stains result from direct contact between a bloody object and a surface; they may show the shape of the object (e.g., footwear, fabric weave).

Scene security and preservation come first: establish a perimeter, log entry/exit, and use a scene log to maintain chain of custody.

The four scene search patterns are line/strip, grid, spiral (inward or outward), and zone/quadrant; choose based on scene size and terrain.

Chain of custody must record every transfer of evidence: collector, date/time, location, description, and each subsequent handler.

Sketching conventions: note the datum point and reference measurements; include case number, scale, compass direction, and legend.

Photograph the scene before alteration: overall, mid-range, and close-up with and without a scale.

Physical evidence classes include transient (perishable), pattern, conditional, transfer, and associative evidence.

Biological evidence should be air-dried and packaged in paper; wet items in plastic risk mold and degradation.

The CSI's role is documentation and collection, not determination of guilt; interpretations belong to the analyst/examiner.

Contamination control: change gloves between items, use disposable tools, and avoid talking/coughing over DNA-bearing evidence.

Footwear impressions are classified as latent (invisible, e.g., on paper), patent (visible, e.g., in mud or blood), or plastic (3D, e.g., in snow or soft soil).

Casting 3D impressions uses dental stone; mix to a consistency that flows into detail, and reinforce with a support structure for large prints.

Lifting 2D impressions: electrostatic dust print lifter for dry residue on hard surfaces; gelatin or adhesive lifters for dust on porous surfaces.

Examination compares class characteristics (general pattern, size, manufacturer design) and individual characteristics (wear, cuts, embedded debris).

Tread design and manufacturing marks identify the brand/model; individual wear patterns and accidental marks may allow source attribution.

Photograph footwear impressions with an oblique light source and an ABFO-style scale; fill the frame and keep the film plane parallel.

Tire impressions: record track width, wheelbase, and tread design; sidewall markings and tread wear help identify the tire.

Enhancement techniques include powder, dye stains, chemical reagents (e.g., leucocrystal violet for blood), and oblique lighting.

Elimination prints from scene personnel and known shoes should be collected to distinguish scene-related impressions.

Forensic art includes composite drawing, age progression, image enhancement, demonstrative evidence, and postmortem reconstruction.

Composite drawing relies on witness interview techniques: cognitive interview, open-ended questions, and feature-by-feature recall.

Facial features are described by type (e.g., nose shape, eye spacing, hairline) using standardized reference charts to reduce ambiguity.

Age progression uses known aging patterns: craniofacial growth, skin laxity, weight changes, and lifestyle factors.

Two-dimensional reconstruction from the skull uses tissue-depth data (average thickness at landmarks) to estimate facial contours.

Three-dimensional clay reconstruction builds tissue depth markers at anthropometric landmarks before sculpting muscle and skin.

Demonstrative evidence (e.g., diagrams) must be accurate and non-prejudicial; it illustrates testimony rather than replacing it.

Image enhancement for identification should preserve original files and document every alteration to maintain admissibility.

The photographic triad: aperture controls depth of field, shutter speed controls motion blur, and ISO controls sensor sensitivity/noise.

Use a 1:1 reproduction ratio (or fill-the-frame) for evidence close-ups; include a scale (e.g., ABFO No. 2) in the same plane as the evidence.

Depth of field increases with smaller aperture (larger f-number); for macro work, use f/16–f/22 and a tripod.

Oblique lighting reveals texture (e.g., tool marks, impressions); diffuse lighting reduces shadows; backlighting silhouettes transparent evidence.

Photograph overall (wide), mid-range, and close-up views; include a scale in each close-up and note orientation/direction.

Alternate light sources (UV, IR, forensic light) reveal latent evidence such as biological fluids or altered documents.

Digital image integrity: preserve original files, use write-once media, and document any enhancement steps.

Photogrammetry and 3D scanning can document scene geometry; measurements require calibrated references.

Video evidence must be preserved in its original format; avoid transcoding before analysis, and hash the original file.

Frame rate and time base: know the camera's frames per second to calculate time intervals between events.

Enhancement (contrast, brightness, sharpening) should be documented and applied to copies, never the original.

Measurement of speed/distance from video requires known reference distances and camera calibration (e.g., using a known object).

Facial identification from video is limited by resolution, angle, and lighting; compare with caution and document limitations.

Chain of custody for video includes the recording device, storage media, and any transfer or copy process.

Video metadata (timestamp, codec, resolution) can be altered; verify with original device and hash values.

Multi-camera synchronization helps reconstruct events across views; note camera positions and fields of view.

Latent prints are invisible deposits of sweat and oils; development methods depend on the surface: porous vs. non-porous.

Porous surfaces (paper, cardboard): use ninhydrin, DFO, or physical developer; non-porous (glass, metal): use powder, cyanoacrylate fuming, or vacuum metal deposition.

Cyanoacrylate (superglue) fuming develops latent prints on non-porous surfaces; follow with dye staining (e.g., rhodamine) for contrast.

Ninhydrin reacts with amino acids in sweat; it is used on porous surfaces and requires heat/humidity for development.

ACE-V: Analysis, Comparison, Evaluation, and Verification - the standard latent print examination methodology.

Individualization requires agreement of sufficient ridge characteristics (minutiae) such as ridge endings, bifurcations, and islands.

Ridgeology considers ridge flow, ridge characteristics, and pores; clarity and distortion affect the value of the print.

Photograph latent prints with oblique or coaxial lighting; use a scale and record the development method.

AFIS searches latent prints against tenprint databases; the examiner makes the final identification, not the system.

Tenprint cards record rolled impressions of all ten fingers plus plain (slap) impressions; rolled prints capture the full ridge area.

Fingerprint patterns: arches (plain, tented), loops (ulnar, radial), and whorls (plain, central pocket, double loop, accidental).

Ridge count: the number of ridges between the delta and the core; used in classification and comparison.

Henry classification system uses pattern types and ridge counts to group tenprint records for manual filing.

AFIS/NGI searches tenprints against latent and tenprint databases; candidates are reviewed by a trained examiner.

Quality control: check for smudging, missing fingers, and correct finger labels; reject and reprint poor impressions.

Palm prints and major case prints supplement tenprints for identification.

Fingerprint comparison follows ACE-V; verification by a second examiner is standard practice.