Crime Scene Investigation Techniques

Why This Matters

Crime scene investigation sits at the intersection of science and justice—it's where physical evidence meets legal accountability. You're being tested not just on what investigators do, but on why each technique matters for establishing facts in court. Understanding the scientific principles behind evidence collection—chain of custody, Locard's exchange principle, pattern analysis, and biological degradation—will help you connect individual techniques to broader criminological concepts like evidentiary standards, wrongful conviction prevention, and the forensic science reform movement.

Don't just memorize a list of techniques. Know what each method proves, why contamination destroys its value, and how different evidence types work together to reconstruct criminal events. When you encounter exam questions about forensic evidence, you should immediately think: What does this technique establish? How could it be compromised? What legal standards must it meet?

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Scene Management and Documentation

Before any evidence can be analyzed, it must be protected and recorded. These foundational techniques establish the integrity and context that make all subsequent analysis legally admissible.

Securing and Isolating the Crime Scene

• Perimeter establishment—first responders create physical boundaries using tape, cones, or officers to prevent contamination from unauthorized personnel
• Access control logs document every person entering the scene, creating accountability and supporting later challenges to evidence integrity
• Scene integrity directly impacts admissibility; a compromised scene gives defense attorneys grounds to challenge all evidence collected

Documenting the Scene Through Photography and Sketching

• Systematic visual documentation captures wide-angle context shots and close-up evidence photos before anything is moved or collected
• Measured sketches provide spatial relationships between evidence items, victim positions, and entry/exit points—critical for reconstruction
• Time-stamped records establish scene conditions at discovery, which becomes essential when analyzing evidence degradation or witness timelines

Chain of Custody Procedures

• Continuous documentation tracks evidence from collection through court presentation, with every transfer logged and authorized
• Tamper-proof packaging using sealed containers and signature strips prevents and reveals any unauthorized access
• Legal foundation—breaks in chain of custody can render even conclusive forensic evidence inadmissible, making this the backbone of forensic credibility

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Biological Evidence Analysis

Biological evidence provides the strongest links between suspects and crime scenes through Locard's exchange principle—the idea that every contact leaves a trace. These techniques identify individuals and reconstruct events through bodily materials.

DNA Collection and Analysis

• Biological sample collection (blood, saliva, hair with follicles) requires sterile tools and proper storage to prevent degradation of genetic material
• PCR amplification allows analysis of minute samples by copying DNA segments millions of times, revolutionizing cold case investigations
• DNA profiling creates unique genetic fingerprints with accuracy rates exceeding 99.9%, though contamination or degraded samples remain significant limitations

Fingerprint Analysis and Collection

• Latent print visualization uses powders, chemicals (ninhydrin, cyanoacrylate fuming), or alternate light sources to reveal invisible prints on various surfaces
• AFIS databases enable rapid comparison of collected prints against millions of records, dramatically accelerating suspect identification
• Uniqueness and permanence—fingerprints remain unchanged throughout life and no two individuals share identical patterns, making them powerful individualizing evidence

Blood Spatter Analysis

• Pattern interpretation examines shape, size, and distribution of bloodstains to determine the dynamics of violence—impact velocity, directionality, and number of blows
• Geometric reconstruction uses spatter angles to calculate the point of origin, revealing victim and assailant positions during the attack
• Limitations acknowledged—this field has faced scientific scrutiny, and examiners must distinguish between what patterns definitively prove versus suggest

Toxicology Analysis

• Biological screening of blood, urine, and tissue samples detects drugs, alcohol, poisons, and therapeutic medications
• Concentration analysis determines not just presence but levels, which indicates whether substances contributed to incapacitation or death
• Behavioral reconstruction—toxicology results help establish victim or suspect mental state, supporting or undermining claims of intent, self-defense, or diminished capacity

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Trace and Transfer Evidence

Trace evidence demonstrates contact between people, objects, and locations. These microscopic materials often go unnoticed by perpetrators but provide crucial corroborating evidence.

Trace Evidence Collection (Hair, Fibers, Etc.)

• Meticulous collection using tweezers, tape lifts, or vacuuming captures materials invisible to the naked eye without introducing contamination
• Individualized packaging prevents cross-contamination between samples, which would destroy their evidentiary value
• Corroborative power—trace evidence rarely identifies a specific individual but powerfully supports or contradicts suspect narratives about presence at a scene

Forensic Entomology

• Insect specimen collection from remains provides biological clocks through analysis of species present and their developmental stages
• Post-mortem interval estimation uses known insect life cycles to calculate minimum time since death, often more reliable than other methods for decomposed remains
• Environmental context—temperature, humidity, and access to remains affect insect colonization, requiring careful documentation of scene conditions

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Pattern and Impression Evidence

Pattern evidence captures the physical signatures left by objects at crime scenes. These techniques link specific items—shoes, tires, weapons—to the scene through unique wear patterns and manufacturing characteristics.

Footwear and Tire Track Impression Analysis

• Casting techniques using dental stone or silicone preserve three-dimensional detail from impressions in soil, snow, or soft surfaces
• Class vs. individual characteristics—size and tread pattern narrow possibilities to a type, while unique wear marks and damage can identify a specific shoe or tire
• Scene reconstruction value—impression evidence establishes movement patterns, number of perpetrators, and entry/exit routes

Ballistics and Firearm Evidence Examination

• Projectile and casing collection preserves striations and firing pin marks that link bullets and casings to specific weapons
• Trajectory analysis uses bullet holes, ricochet marks, and wound patterns to reconstruct shooter position and sequence of shots
• NIBIN database comparison connects firearm evidence across cases, potentially linking seemingly unrelated crimes to the same weapon

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Digital and Reconstructive Analysis

Modern investigations increasingly depend on electronic evidence and systematic reconstruction. These techniques synthesize multiple evidence types into coherent narratives.

Digital Forensics and Electronic Evidence Collection

• Device seizure protocols prevent data destruction through immediate isolation from networks and use of Faraday bags to block remote wiping
• Forensic imaging creates bit-by-bit copies of storage media, preserving metadata and deleted files while maintaining original evidence integrity
• Expanding scope—digital evidence now includes cloud data, social media activity, GPS records, and IoT device logs, requiring continuous adaptation of forensic methods

Crime Scene Reconstruction

• Evidence synthesis combines physical evidence, witness statements, and forensic analysis to recreate the sequence of events
• Hypothesis testing uses reconstruction to evaluate competing theories about what occurred, eliminating scenarios inconsistent with evidence
• Court presentation—diagrams, 3D models, and animations help juries understand complex spatial and temporal relationships

Forensic Anthropology Techniques

• Skeletal analysis determines biological profile (age, sex, ancestry, stature) from human remains when soft tissue identification is impossible
• Trauma interpretation distinguishes ante-mortem, peri-mortem, and post-mortem bone damage to establish cause and manner of death
• Identification collaboration—anthropologists work with odontologists and DNA analysts to identify unknown remains, crucial in mass disasters and cold cases

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Quick Reference Table

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Self-Check Questions

1. Which two techniques both establish individual identification but differ in whether they can work with degraded samples? What makes one more reliable than the other for cold cases?

2. A defense attorney argues that evidence was contaminated. Which techniques and procedures would the prosecution use to counter this claim, and how do they work together?

3. Compare and contrast how blood spatter analysis and forensic entomology each contribute to reconstructing a crime's timeline. What different questions does each answer?

4. If an FRQ asks you to explain how Locard's exchange principle applies to crime scene investigation, which three techniques would best illustrate your answer and why?

5. A body is discovered in a remote location with skeletal remains and insect activity. Which combination of forensic techniques would investigators prioritize, and what specific information would each provide?