IAI SP9 flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Angle of impact formula

The impact angle of a blood droplet is calculated as the inverse sine of width divided by length of the stain. The width is the minor axis and the length is the major axis.

Area of origin calculation

Lines drawn through the long axes of several stains converge at a point. Height above that point for each stain is distance times tangent of the impact angle.

Cast-off pattern

A linear trail of bloodstains along the arc of a swinging object, with stains decreasing in size as the weapon slows. Each swing creates a separate trail.

Expirated blood pattern

Fine blood mist containing air bubbles or mucous strands, produced from the mouth or nose. It is often found on surfaces near the victim's face.

Void pattern

An absence of bloodstaining where an intervening object blocked deposition. It can indicate the position of a person or object at the time of the event.

Chain of custody elements

A record of every transfer of evidence, including item number, description, collector, date and time, and the receiving party. Gaps can affect admissibility.

Grid search pattern

Two passes over the scene at right angles to each other, providing thorough coverage of an area. It is slower than a line search but reduces missed evidence.

Locard's exchange principle

Every contact between two objects leaves a trace of one on the other. Investigators treat the scene as a source of transfer evidence.

Packaging biological evidence

Damp biological items are air-dried and packaged separately in paper containers. Airtight plastic is avoided because moisture promotes degradation and contamination.

Three levels of footwear detail

Class characteristics include manufacturer, model, and size. Design characteristics include wear and damage. Individual characteristics include random cuts, nicks, and embedded objects.

Electrostatic lifting

A method for recovering dry dust footwear impressions from hard surfaces using a charged film. It is not suitable for impressions in blood or on porous surfaces.

Tire track comparison elements

Comparison uses tread design, tread width, track width, and circumference. Wear patterns and irregular damage may support individualization to a specific tire.

Footwear size limitation

Shoe size is a class characteristic and cannot identify a wearer. It can only suggest a range of possible wearers or exclude some individuals.

Tissue-depth markers

Pins or markers placed at standard facial landmarks during reconstruction, using population-specific tissue-depth tables. They guide the rebuilding of soft tissue over the skull.

Cognitive interview

A witness interviewing technique using open-ended prompts and free recall to reduce suggestion. The witness's own words are recorded and leading questions are avoided.

Composite image limitation

A composite is an investigative lead, not a positive identification. It is released with the caveat that facial features may vary from the actual person.

Frankfort horizontal plane

A reference plane through the upper margin of the external ear canal and the lowest point of the orbital rim. It is used to orient profile reconstruction.

Exposure triangle

Aperture controls depth of field, shutter speed controls motion blur, and ISO controls sensor sensitivity and image noise. The three settings balance to achieve correct exposure.

Three-scale scene photography

Overall photographs show the whole scene, mid-range photographs show evidence in context, and close-ups show detail with a scale in the same plane.

Oblique lighting use

Light directed at a low angle across a surface reveals texture, indentations, and surface detail. It is used for footwear impressions and tool marks.

Digital image integrity

The original file is preserved unaltered, and every enhancement step is documented with an audit trail. Enhancement cannot add information absent from the original.

DVR export best practice

Export the native file together with its player, and document any re-encoding or screen capture. Preserve hash values and maintain a chain of custody for the digital file.

Video time offset

The difference between the recorder's clock and the known incident time, established from a reference event. It is recorded as a correction factor for the analysis.

Height estimation from video

Uses the pinhole camera model with a reference object of known height in the same plane as the subject. Lens distortion and pixel aspect ratio are corrected first.

Interlaced video fields

Each frame of interlaced video contains two fields recorded at different moments. Deinterlacing choices affect measurements and must be documented.

ACE-V process

Analysis, Comparison, Evaluation, and Verification. Verification is an independent examination by another qualified examiner before a conclusion is reported.

Cyanoacrylate fuming

A development technique for latent prints on non-porous surfaces, such as plastic and metal. The print may then be enhanced with powder, dye stain, or alternate light.

Ninhydrin development

A reagent that reacts with amino acids in latent print residue on porous surfaces such as paper. It produces a purple reaction product, often enhanced with heat.

Levels of print detail

Level 1 is ridge flow and pattern, Level 2 is minutiae or ridge path, and Level 3 is pores, ridge width, and edge shape.

Henry classification values

In the Henry system, arch and tented arch are assigned 0, loop is 1, and whorl is 2. Values on even and odd fingers build the primary classification ratio.

Ridge counting rule

Ridges are counted along a straight line from the delta to the core. The count excludes the delta and the core themselves.

Rolled versus plain impressions

Rolled impressions capture each finger from edge to edge on a tenprint card. Plain impressions are taken simultaneously and verify that the rolls are complete and correctly ordered.