12.1 Crime Scene Management & Evidence Handling

12.1 Crime Scene Management & Evidence Handling

The integrity of a criminal investigation hinges directly upon the actions taken by law enforcement officers during the initial stages of a crime scene response. Under Pennsylvania Municipal Police Officers' Education and Training Commission (MPOETC) standards and Pennsylvania criminal procedure, proper scene management, systematic search protocols, meticulous evidence preservation, and strict chain of custody documentation are mandatory to ensure that physical evidence remains admissible in a court of law.

First Responder Responsibilities

When a police officer arrives as the first responder at a crime scene, primary duties must be executed in a rapid, prioritized sequence. The paramount objective is the protection of human life, followed immediately by the preservation of the crime scene.

Primary Operational Sequence

1. Ensure Officer and Public Safety: Assess the scene for ongoing threats, such as active shooters, hazardous materials, structural dangers, or fleeing suspects.
2. Render Emergency Medical Aid: Provide immediate emergency first aid to injured victims or suspects. Medical personnel must be directed along a designated entry path to minimize disturbance to physical evidence. If a victim must be transported to a medical facility, an officer should accompany the victim or document EMT information to collect clothing and dying declarations.
3. Secure the Crime Scene and Establish Perimeters: Establish physical boundaries using barrier tape, barricades, or officer posts to prevent unauthorized entry and contamination.
   • Inner Perimeter: Surrounds the immediate area where the crime occurred, including entry and exit paths, victim location, and primary evidence concentrations. Access is strictly restricted to essential forensic personnel and primary investigators.
   • Outer Perimeter: Surrounds the inner perimeter and serves as a buffer zone. It encompasses the command post, staging areas for equipment, media coordination points, and patrol unit positions.
4. Establish a Crime Scene Entry Log: A dedicated officer must be stationed at the single designated access point of the inner perimeter to maintain an official Crime Scene Entry Log. This log must record the name, rank, agency, badge number, date, time of entry, time of exit, and specific reason for entry for every individual entering the scene.
5. Detain Witnesses and Suspects: Separate witnesses immediately to prevent collusion or memory contamination, obtain initial identification, and secure suspects.

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Crime Scene Search Patterns

Once the scene is secured and preliminary documentation (photography and videography) is underway, investigators must conduct a systematic search. Choosing the appropriate search pattern depends on the size of the area, terrain, indoor versus outdoor setting, number of search personnel, and the nature of the evidence sought.

Detailed Search Methodologies

• Strip/Line Search: Search personnel form a straight line and advance slowly at the same pace across a designated search area. This pattern is highly effective for open fields when searching for discarded weapons, shell casings, or missing persons.
• Grid Search: A modification of the strip search where searchers complete a full line search in one direction (e.g., north to south) and then repeat the search along lines perpendicular to the first pass (e.g., east to west). This double-coverage approach provides maximum thoroughness for locating trace evidence, small shell casings, or dropped items.
• Zone/Sector Search: The scene is divided into manageable geometric zones (such as Room A, Room B, vehicle interior, or quadrant 1). A specific investigator is assigned responsibility for searching and documenting each designated sector. This method is standard for search warrants in residential homes or multi-story structures.
• Spiral Search: Searchers move in a continuous circular pattern, either starting at the outer perimeter and moving inward toward the center (inward spiral) or starting at the focal point of the crime scene and spiraling outward (outward spiral). This method works well in open fields or water search operations where physical boundaries are absent.
• Wheel/Ray Search: Searchers start at a central focal point and walk outward along straight radial paths like spokes on a wheel. While less common due to unsearched gaps between rays as distance increases, it is particularly effective for blast sites or localized explosions.

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Evidence Types & Preservation

Evidence collected at a crime scene falls into major categories including physical, biological, latent, and digital evidence. Each category demands specific handling protocols to prevent contamination, degradation, or evidentiary compromise.

Physical and Biological Evidence

• Biological / DNA Evidence: Includes blood, semen, saliva, skin cells, hair, and tissue. Investigators must wear personal protective equipment (PPE)—including nitrile gloves, masks, and shoe covers—to prevent introducing host DNA.
  • Packaging Mandate: Biological evidence must be thoroughly air-dried at room temperature and packaged exclusively in breathable paper bags or cardboard boxes. Sealing wet biological evidence in plastic bags traps moisture, creating an anaerobic environment that fosters mold growth and rapidly destroys DNA.
• Trace Evidence: Hair, fibers, glass fragments, and soil must be collected using sterile tweezers or vacuum swabbing and placed in paper bindles (pharmacist folds) before secondary packaging in labeled envelopes.

Latent Fingerprints

Latent prints are invisible friction ridge impressions left by natural oils and sweat on surfaces. Processing methods depend on surface porosity:

• Fingerprint Powders (Black / Magnetic Powder): Applied with a camel hair or fiberglass brush to non-porous, smooth surfaces (glass, painted metal, glazed tile). Lifted using transparent fingerprint tape and mounted on a backing card.
• Cyanoacrylate (Superglue Fuming): Used for non-porous items such as firearms, plastic bags, and metal tools. Warmed cyanoacrylate vapors react with moisture and amino acids in latent prints to produce a durable, white polycyanoacrylate deposit that can be photographed and dusted.
• Ninhydrin Processing: Applied to porous surfaces such as paper, cardboard, and untreated wood. Ninhydrin reacts with amino acids present in sweat to yield a purple-colored impression known as "Ruhemann's purple."

Digital Evidence

Digital evidence includes smartphones, tablets, laptops, hard drives, and flash media.

• Signal Isolation: Mobile devices must be placed immediately into a Faraday bag or RF shielding enclosure to block cellular, Wi-Fi, Bluetooth, and GPS signals. This prevents remote wiping, encryption commands, or signal alteration by co-conspirators.
• State Preservation: If a computer is powered on at the scene, investigators trained in digital forensics must capture volatile RAM memory before shutting the system down. Unpowered devices should remain off during transport.

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Chain of Custody Documentation

The chain of custody is the unbroken, chronological record tracking the seizure, custody, control, transfer, analysis, and disposition of physical and electronic evidence. Under Pennsylvania rules of evidence, any gap or unexplainable break in the chain of custody can lead to defense motions to suppress evidence, rendering critical exhibits inadmissible at trial.

Mandatory Documentation Steps

1. Property Tags & Evidence Logs: Every item seized must be assigned a unique item number and logged on an official Evidence Log. Property tags affixed to packaging must record:
   • Incident / Case Number
   • Date and time of recovery
   • Exact physical location recovered (e.g., "North bedroom floor, 3 feet east of bed frame")
   • Full name, badge number, and signature of the recovering officer
   • Detailed item description, including make, model, color, and serial numbers
2. Transfer Logs: Whenever evidence changes hands—whether transferred to a property clerk, delivered to the Pennsylvania State Police Crime Lab, or presented in court—a physical or electronic transfer receipt must be executed. The log must capture the date, time, relinquishing party's signature, receiving party's signature, and specific purpose of the transfer.
3. Storage Security: Evidence must be secured in a temperature-controlled, limited-access property locker with restricted keycard or logbook access to prevent tampering, theft, or environmental degradation.