Rotation 1 – Scene Documentation, Photography, and Evidence Collection — Crime Scene / Forensic Technician

Objective. The student will independently or co-operatively document at least five scenes or evidence submissions using photography, sketching, and written notes that meet agency and IAI CCSI competency standards.

Rotation 1 – Scene Documentation, Photography, and Evidence Collection

Your first externship rotation places you directly in an agency environment where real cases are processed, real evidence is handled, and real chain-of-custody records are signed. Everything you do here carries legal weight. Work carefully, ask questions, and never act outside your supervisor's authorization.

Scene Photography: The Overview–Midrange–Close-Up Sequence

Every scene you photograph must be documented in a logical, court-defensible progression. The agency standard — and the IAI CCSI competency expectation — requires three tiers of coverage.

Overview (establishing) shots capture the entire scene and its relationship to fixed landmarks such as streets, building entrances, and vehicles. Shoot from multiple compass points so that any viewer can orient themselves without visiting the site.

Midrange shots close the distance to a specific area of interest — a broken window, a bloodstain pattern, a tire impression. The viewer should be able to locate the subject within the larger scene.

Close-up shots fill the frame with the evidence item itself. Always take two close-up images of each item: one without a scale and one with an ABFO No. 2 ruler or agency-approved scale ruler placed beside (never on top of) the item. Record camera model, lens focal length, aperture (f-stop), shutter speed, ISO, white-balance setting, flash or lighting used, and ambient conditions in your annotated image log sheet at the time of capture — not later.

If you must move the camera or change settings between shots, note the change on the log. Courts have rejected photo evidence because metadata contradicted written logs. Consistency and accuracy protect the case.

Scene Sketches: Permanent Dimensional Records

Photographs can distort perspective. A to-scale sketch is often the most trusted dimensional record in a courtroom. Your sketch must include:

A north arrow (obtain compass bearing or confirm with agency mapping tools)
A written scale (e.g., 1 inch = 4 feet) or the notation "not to scale" with all measurements written in
All measurements recorded by two-point measurement or triangulation from fixed reference points
A legend identifying every symbol used
Your name, date, case number, and supervisor's signature before it enters the file

Two-point measurement locates an item by measuring its distance from two fixed, permanent reference points (e.g., a wall corner and a door frame). Triangulation uses two measured distances from separate fixed points so that the intersection pinpoints the item — useful in open outdoor scenes with no right-angle walls.

If CAD software is available, confirm with your supervisor which program and file format the agency accepts. Save a backup and a printed copy for the case file.

Evidence Collection: Categories and Packaging

Across your rotation you will collect at least ten items spanning four categories.

Biological evidence (blood, saliva, hair with root) requires paper packaging in most cases. Plastic traps moisture and promotes bacterial growth that destroys DNA. Use paper bags or druggist-fold (bindle) paper, label, and seal.

Impression evidence (footwear, tire, tool marks) should be photographed with oblique lighting before any casting or lifting attempt. Casting materials and lifting tape are chosen after photography is complete.

Trace evidence (fibers, glass fragments, gunshot residue) is extremely fragile. Use forceps, not bare hands. Package in rigid containers or folded paper bindles to prevent cross-contamination. Change gloves between items.

Digital media (phones, USB drives, SD cards) must never be powered on or connected to an unvalidated device. Place in a static-shielding or Faraday bag and document the item's power state at collection.

Chain of Custody: The Unbroken Record

Every person who touches an evidence item must be documented. The chain-of-custody form captures: who collected the item, when, where, its condition, and every subsequent transfer. A single undocumented transfer can make evidence inadmissible.

Before handing any package to the evidence room, your supervisor will verify it against the agency's standard evidence submission checklist. Errors found at that stage require corrected documentation and resubmission — the original flawed form is retained in the file as a record of the correction, never discarded.

Safety on Scene

Assume all biological material is potentially infectious. Wear nitrile gloves, safety glasses, and a mask as a minimum; wear a full face shield and Tyvek suit if blood or body fluids are present in quantity.
Sharp objects (needles, broken glass, knives) go into rigid puncture-resistant containers — never loose into a paper bag.
If a scene is not yet cleared by law enforcement as safe, you do not enter. Confirm scene clearance with the lead officer before approaching.
Tag and isolate any chemical hazard (unknown substances, fuel spills) and notify your supervisor immediately. Do not collect unknown chemicals without a hazmat-trained officer present.
Photograph your PPE donning and doffing sequence if agency protocol requires it; this documents that contamination controls were followed.

Key terms10

Overview shotA wide-angle photograph that establishes the entire scene and its relationship to surrounding fixed landmarks, taken before any evidence is moved.

Midrange shotA photograph taken at an intermediate distance that places a specific area of interest within the broader context of the scene.

Close-up shotA photograph that fills the frame with a single piece of evidence; taken twice — once without a scale and once with an approved scale ruler placed beside the item.

Two-point measurementA method of locating an item's position by measuring its straight-line distance from two separate fixed reference points in a scene.

TriangulationA scene-measurement technique that uses two measured distances from different fixed points whose intersection precisely locates an item; especially useful in open outdoor scenes.

Chain of custodyThe documented, unbroken record of every person who collected, transferred, examined, or stored a piece of evidence from the moment of collection through final disposition.

Bindle (druggist fold)A method of folding paper into a self-sealing packet used to package small or trace evidence items to prevent loss or cross-contamination.

Faraday bagA shielded pouch that blocks wireless signals, used to isolate digital devices and prevent remote data wiping or alteration after collection.

Annotated image logA written record completed at the time of photography that captures camera settings, lighting conditions, scale references, and image sequence for each photograph taken at a scene.

Oblique lightingA technique in which a light source is held at a low angle to the surface to cast shadows that enhance the three-dimensional detail of impression evidence before casting or lifting.

Worked examples3

1. You photograph a shoe impression. The image log requires you to record magnification data. Your lens is set to 50 mm focal length, aperture f/8, shutter 1/60 s, ISO 400. The impression measures 30 cm long. Your close-up frame width in the viewfinder spans 35 cm. What is the approximate reproduction ratio (image size : subject size) for this shot, and what does that tell you about whether the ABFO scale in the frame will be accurate?

Step 1 – Identify the sensor or film frame width. A full-frame DSLR sensor is 36 mm (3.6 cm) wide.
Step 2 – The subject width in the frame is 35 cm. Reproduction ratio = sensor width ÷ subject width = 3.6 cm ÷ 35 cm ≈ 0.10 : 1 (roughly 1:10 scale).
Step 3 – At 1:10, the ABFO scale in the frame is also reproduced at 1:10. As long as the scale is in the same focal plane as the impression surface and the camera back is parallel to the ground, the scale will render accurately and measurements taken from the print will be reliable.
Step 4 – Record in the log: 50 mm lens, f/8, 1/60 s, ISO 400, ambient overcast daylight, supplemental oblique flashlight at approximately 15° from the left. Note 'scale in frame, same plane as impression.'

Answer: Reproduction ratio ≈ 1:10. Because the ABFO scale occupies the same focal plane as the impression, it will reproduce at the same ratio and measurements from the photograph will be accurate, provided the camera back is held parallel to the surface.

2. You must locate a bloodstain on a hardwood floor using two-point measurement. Fixed Point A is the northeast corner of the room. Fixed Point B is the base of a door frame 4.2 m directly west of Point A along the north wall. You measure: stain to Point A = 2.1 m; stain to Point B = 2.7 m. Confirm that these distances are geometrically consistent (i.e., the stain is inside the room and not on the wall) by checking the triangle inequality.

Step 1 – Label the three sides of the triangle: side a (Point A to Point B) = 4.2 m; side b (Point B to stain) = 2.7 m; side c (Point A to stain) = 2.1 m.
Step 2 – Apply the triangle inequality: each side must be less than the sum of the other two. Check: 4.2 < 2.7 + 2.1 → 4.2 < 4.8 ✓; 2.7 < 4.2 + 2.1 → 2.7 < 6.3 ✓; 2.1 < 4.2 + 2.7 → 2.1 < 6.9 ✓.
Step 3 – All three inequalities hold, so a valid triangle exists and the stain can be plotted at the unique intersection of a 2.1 m arc from A and a 2.7 m arc from B.
Step 4 – Draw arcs on the sketch at those radii from each fixed point; mark the intersection south of the north wall. Record all three measurements on the sketch legend.

Answer: The triangle inequality is satisfied on all three checks, confirming the measurements are geometrically consistent. Plot the stain at the intersection of a 2.1 m arc from Point A and a 2.7 m arc from Point B on the sketch.

3. You are logging photographs of a scene with 18 shots. Images 1–4 are overview shots, images 5–10 are midrange, and images 11–18 are close-ups (each evidence item shot once without scale and once with scale, totaling 4 items × 2 shots). How many distinct evidence items received a complete close-up documentation set, and what is the minimum number of additional shots needed if a supervisor finds that one item's 'with-scale' image is out of focus?

Step 1 – Close-up shots total 8 (images 11–18). Each item requires 2 shots (without scale + with scale), so number of items = 8 ÷ 2 = 4 items.
Step 2 – One item's 'with-scale' image is unusable. That item's documentation set is incomplete.
Step 3 – To remedy, retake the 'with-scale' close-up for that item: minimum 1 additional shot needed. (Best practice is to take 2–3 retakes and select the sharpest; however, the minimum to meet the 'complete set' requirement is 1 acceptable image.)
Step 4 – Record the retake in the image log with a notation explaining why it was taken, cross-referencing the original image number.

Answer: Four distinct evidence items received close-up coverage. At minimum, 1 additional retake of the 'with-scale' shot is required to complete that item's documentation set; the retake must be noted in the annotated image log.

The math in this lesson1

In class: Under supervisor oversight, photograph a minimum of five scenes or evidence sets using the agency's established overview-midrange-close-up sequence; submit each image set with an annotated log sheet showing camera settings, lighting conditions, and scale references. · Prepare hand-drawn or CAD-assisted scene sketches for at least three assignments, including north arrow, scale, measurements taken by two-point or triangulation method, and a legend; have the supervisor review and sign each sketch before it enters the case file. · Collect, package, and complete chain-of-custody documentation for at least ten evidence items across different categories (biological, impression, trace, digital media); supervisor uses the agency's standard evidence submission checklist to verify each package before submission to the evidence room.
Materials: Agency-issued DSLR or mirrorless camera, tripod, scale rulers, measuring tape, total station or measuring wheel (if available), sketch paper or CAD software, evidence packaging supplies (paper bags, plastic bags, bindle paper, evidence tape, tamper-evident seals), chain-of-custody forms, agency case management software, IAI CCSI certification candidate handbook
Check: Supervisor scores each documentation set using the agency photo and sketch checklist; all five scene documentation packages must receive a 'meets standard' rating (equivalent to 80% on a 10-point rubric) with no chain-of-custody errors; errors require corrected resubmission before rotation ends.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.