Trauma and Crime Scene Technician cheat sheet

Scene safety is a continuous re-assessment, not a single entry check; re-evaluate at every personnel change, lighting change, and shift handover.

Establish an inner perimeter, an outer perimeter, and a command post; only sworn or authorized personnel cross the inner perimeter, and all crossings are logged.

Universal precautions apply to every scene: assume all blood, urine, saliva, and tissue are infectious regardless of appearance or history.

Structural, electrical, and chemical hazards are cleared by the appropriate specialist (fire, utility, hazmat) before evidence work begins, and the clearance is documented.

Firearms are rendered safe by a qualified person before handling; a weapon is photographed and documented in place, then unloaded following agency procedure with serial number recorded.

Fentanyl and other potent opioids: do not field-test suspected powders; use nitrile gloves, avoid raising dust, and follow naloxone-availability policy for responders.

Carbon monoxide, hydrogen sulfide, and clandestine-lab atmospheres require atmospheric monitoring before entry; a single unresponsive person in an enclosed space is a rescue-with-hazmat scenario, not a lone entry.

Weather, temperature, and time-on-scene are recorded because heat, rain, and UV degrade biological evidence and affect scene reconstruction.

Bloodborne pathogen exposure control relies on engineering controls, work-practice controls, PPE, and hepatitis B vaccination offered at no cost to at-risk employees.

PPE selection is task-based: nitrile gloves for blood and body fluids, eye and face protection for splash risk, fluid-resistant gown or suit for saturation risk, and N95 or higher for aerosol-generating procedures.

Sharps are never recapped by hand; place them in a rigid sharps container at the point of use, and document any needlestick immediately.

Post-exposure steps: wash the site with soap and water, flush mucous membranes, report immediately, and seek source testing and prophylaxis per protocol; time to prophylaxis matters.

Decontamination sequence is outside-in and top-down; remove PPE without touching the outer surface, bag it as biohazard waste, then wash hands.

Biohazard waste is segregated at the point of generation into labeled red bags or rigid containers; liquid blood in quantities is solidified or absorbed per local regulation.

Bloodborne pathogens of concern include HBV, HCV, and HIV; HBV is the most environmentally stable and the most transmissible by needlestick.

Documented exposure records are kept confidential and retained per occupational health regulation, typically 30 years after employment ends.

The first responding officer's duties: render aid, secure the scene, detain witnesses, protect evidence, and start a scene log; the first officer usually does not process the scene.

Scene control uses a command post, a single entry point, a log of all persons entering and leaving with times, and a written scene-security roster.

The lead investigator assigns a scene photographer, evidence collectors, sketch/mapping personnel, and a log keeper; one person may hold multiple roles in a small scene, and roles are documented.

Search patterns are chosen by terrain and scene type: line/strip for open ground, grid for thorough coverage of small areas, spiral for a focal point, zone for large or multi-room scenes, and wheel for a central point in open space.

The scene is processed in a defined order: photograph and document before moving anything, then collect, then release; any deviation is documented with a reason.

Transfer of the scene from first responder to investigator to evidence custodian is documented at each handoff with names, times, and condition of the scene.

Scene release requires documented authority, notification of the property owner, and a record of what was taken and what remains secured.

A written scene narrative, sketch, photo log, and evidence log together form the scene record; a missing element is a defensible gap that opposing counsel will probe.

Chain of custody records every transfer: item number, description, date and time of transfer, releasing person, receiving person, and purpose of transfer.

The evidence log and the chain of custody form are separate documents; the log tracks the scene inventory, the chain tracks custody from collection to disposition.

Each item gets a unique identifier that is written on the item, the packaging, the log, and the report; a mismatched identifier is a documentation defect.

Contemporaneous notes are the foundation of testimony; record times, conditions, persons present, and observations, not conclusions.

Sealed packaging is signed across the seal by the sealer; a broken seal is documented with the reason and the person who broke it.

Gaps in custody are not automatically fatal, but they must be explained; an unexplained gap invites a challenge to authenticity and integrity.

Photographs, sketches, and measurements are documented with a reference to the item number and the direction of the shot or the datum point used.

Reports are written in plain, factual language, distinguish observation from opinion, and use the same terminology as the evidence log to avoid inconsistency.

Evidence categories: testimonial, documentary, physical, and demonstrative; physical evidence is further classed as transient, pattern, conditional, transfer, or associative.

Transient evidence degrades with time or environment (odors, temperature, impressions in snow, blood wetness) and is documented first.

Conditional evidence is produced by an action or event (lights on or off, a door open or closed, a weapon cocked) and must be documented before anything is moved.

Locard's exchange principle: every contact leaves a trace; look for transfer in both directions between suspect, victim, and scene.

Associative evidence links a person to a place or another person (fingerprints, DNA, footwear, fibers, digital device data).

Negative evidence is the absence of something expected (no blood where a wound should have bled, no forced entry) and must be documented as found.

Document the item in place, then in relation to a scale and a fixed reference, then collect; moving before documenting destroys context.

Fragile and perishable evidence (biological, digital, volatile) is prioritized for collection, and its condition at collection time is recorded.

Paper packaging is used for biological and damp items so they can dry and breathe; plastic is used for non-biological items that need moisture protection.

Each item is packaged separately; never combine items from different locations or different suspects in one container.

Wet biological items air-dry at room temperature, away from direct heat and sunlight, before sealing; sealing wet items promotes degradation and mold.

Control samples are collected with the evidence: substrate controls for stains, buccal reference standards from known persons, and blank swabs for reagent testing.

Lift techniques: powder and tape for non-porous latent prints, casting compound for impressions in soil or snow, and gel or electrostatic lifters for dust impressions.

Firearms are unloaded, made safe, and packaged in a rigid container with the magazine and cartridges separately secured; do not insert items into the barrel.

Digital devices are isolated from networks (airplane mode or Faraday bag) and powered per policy; do not browse the device, and document the state at seizure.

Storage conditions are recorded: temperature, humidity, and light exposure for biological evidence, and dry, dark, room-temperature storage is the default for DNA-bearing items.

Photographic sequence: overall, mid-range, close-up, and close-up with a scale; every close-up includes a scale and the item number in a second frame.

The photo log records frame number, subject, direction of view, camera settings, lighting, and the photographer; the log makes the image admissible and interpretable.

Use a fixed focal length or set the same zoom for comparison shots; changing focal length between overview and close-up distorts perspective and scale.

Fill the frame with the subject, keep the film or sensor plane parallel to the subject, and use oblique lighting to reveal texture, tool marks, and impression detail.

A scale must be in the same plane as the evidence and labeled with its length; an angled scale misrepresents size.

Mapping methods: baseline or coordinate (two fixed references), triangulation (two datum points), polar (distance and angle from a datum), and total station or photogrammetry for large scenes.

Sketches show the scene to scale with a datum point, north arrow, legend, and measurements; the rough sketch is retained as a record, not discarded.

Video supplements but does not replace still photography; record continuous, narrated sweeps that include the scene entry, and log the recording.

Latent print types: patent (visible, e.g., in blood or ink), plastic (impressed in soft material), and latent (invisible residue, typically eccrine sweat and sebum).

Latent print residue is mostly water and salts with sebaceous oils; it degrades with heat, humidity, and time, and porous surfaces absorb it while non-porous surfaces hold it on the surface.

Processing sequence for non-porous surfaces: visual examination, then powder or cyanoacrylate fuming, then dye stain and laser, then lifting; preserve the item for later DNA sampling.

Porous surfaces (paper, cardboard, untreated wood) are processed with ninhydrin, DFO, or physical developer, and amino acid reagents are applied before or after DNA sampling per lab guidance.

Cyanoacrylate fuming develops prints on non-porous items including plastic bags and metal; dye staining with rhodamine or basic yellow increases contrast under forensic light.

Superglue fuming and powder both contaminate surfaces for some tests; sequence fingerprint and DNA collection so that neither destroys the other, and document the order used.

Known prints (inked or livescan) are collected for elimination, and elimination prints from responders and household members are documented and separated from evidentiary prints.

Documentation: photograph the print in place with a scale before lifting, and record the lift location, technique, and item number on the lift card.

Footwear and tire impressions: photograph with a scale, then cast with dental stone or collect with gel or electrostatic lifters; cast a minimum of two, with a reinforcing material for deep impressions.

Impression evidence is class or individual evidence depending on the number and quality of characteristics; accidental characteristics (cuts, wear, embedded debris) support individualization.

Tool mark evidence: document the tool mark in place, collect the tool or a cast of the mark, and submit both to the lab for comparison; do not test-fit a suspect tool into the mark.

Trace evidence includes hair, fibers, glass, paint, soil, and gunshot residue; collect with clean forceps, tape lifts, or vacuuming, and always collect control samples from the scene.

Glass fracture analysis: radial cracks form first on the opposite side of impact, concentric cracks form on the impact side, and the 3R rule (radial cracks show right angles on the rear) identifies the impact side.

Hair comparison: microscopic characteristics support class association only; nuclear DNA from the root supports individualization, and mitochondrial DNA is maternal lineage evidence.

Gunshot residue collection uses adhesive stubs on the hands and face; results indicate presence of primer elements (lead, barium, antimony), not who fired, and are time-sensitive.

Paint and fiber samples are collected as questioned and known samples from the same area, and each is packaged separately with a location note.

DNA sources: blood, semen, saliva, epithelial cells, hair root, bone, teeth, and touch DNA; the last is low-template and easily contaminated.

Collect the whole item when possible; if swabbing, use a slightly moistened sterile swab, concentrate the stain, air-dry, and submit the swab plus a substrate control.

Avoid excessive moisture, heat, sunlight, and repeated freeze-thaw; store dried biological evidence at room temperature in paper, or frozen for long-term liquid samples.

Prevent contamination: change gloves between items, use disposable tools, speak and cough away from the sample, and wear a mask for touch DNA collection.

Reference samples from known persons are collected with consent or legal authority and are documented; elimination standards from responders are collected when relevant.

Presumptive tests (luminol, Kastle-Meyer, leucomalachite green, acid phosphatase) screen for blood or semen; confirmatory tests (Teichmann, Takayama, RSID, PSA) follow, and results are documented.

Sexual assault evidence collection follows the kit protocol: collect within the kit's time window, maintain drying and packaging order, and document each body site.

Mass disaster and unidentified remains: collect a reference sample from a family member for comparison and record the chain of custody for each sample.

Bloodstain pattern categories: passive (drip, flow, pool), spatter (impact, cast-off, arterial, expiratory), and altered (void, wipe, transfer, saturation).

Impact spatter is driven by force; the higher the energy, the smaller the droplets, but the relationship is not a reliable measure of the number of blows.

Cast-off patterns form linear trails of droplets from a bloody object in motion; direction of travel and the number of swings are interpreted cautiously.

Arterial spatter shows a repeating pattern from a breached artery, with droplets varying in size and direction as the victim or source moves.

Angle of impact: sin θ = width / length of an elliptical stain; the angle is derived from the stain's dimensions, and the direction of travel is from the round end toward the tail.

Area of origin is estimated by projecting lines through the long axes of stains back to a point in space; the result is an estimate, not a precise location.

Void patterns are absences of stain where an object blocked the blood; they indicate the position of an object or person at the time of deposition.

Documentation: photograph each pattern with a scale and label, record the surface and its orientation, and avoid cleaning or moving items before documentation.

Forensic pathologist determines cause (the disease or injury that produced death), mechanism (the physiological derangement), and manner (natural, accident, suicide, homicide, undetermined).

Livor mortis (dependent lividity) begins within about 1-2 hours, becomes fixed in roughly 8-12 hours, and indicates body position after death.

Rigor mortis begins in small muscles within about 2-4 hours, peaks around 12 hours, and resolves in 24-48 hours; it is affected by temperature and body mass.

Algor mortis is postmortem cooling; the rate depends on ambient temperature, body mass, clothing, and air movement, so it is used as a range, not a precise time.

Sharp-force injury: incised wounds are longer than deep, lacerations are deeper than long with tissue bridging; the distinction matters for weapon and mechanism.

Blunt-force injury: contusions, abrasions, and lacerations; pattern injuries (e.g., from a belt buckle or shoe sole) can be compared to a suspected object.

Gunshot wounds: entrance wounds show abrasion rings and soot or stippling at close range; exit wounds are typically larger and irregular, and the track is documented.

The death investigator documents the body position, lividity, rigor, injuries, and scene conditions, and secures the body and personal property under chain of custody.

The Fourth Amendment governs searches and seizures; a warrant, valid consent, exigent circumstances, or another recognized exception is required for a lawful search.

The plain view doctrine requires lawful presence, lawful access, and immediately apparent evidentiary character; it does not authorize a general search.

Chain of custody and authentication are evidentiary foundations; the proponent must show the item is what it is claimed to be and has not been materially altered.

Daubert and Frye standards govern expert testimony; the court considers testability, peer review, error rate, and general acceptance.

Expert testimony must stay within the witness's training and experience; opinions outside that scope are objectionable and damage credibility.

Testimony rules: answer only the question asked, do not guess, distinguish what you observed from what you were told, and correct errors immediately.

Ethical duties include impartiality, truthful reporting of results including inconclusive findings, and disclosure of exculpatory evidence.

Contemporaneous, legible notes and reports are the best defense on the stand; if the report and testimony differ, the report controls and the discrepancy must be explained.