Flashcards Chapter Review: Introduction to Criminal Evidence

Evidence in Criminal Investigations: From Discovery to Forensic Culture

• Overview: The process starts with locating physical evidence, then identifying what it is, collecting it, handling it properly, cataloging it, and preparing it for analysis. This sequence goes beyond mere discovery of a blood droplet or hair; it encompasses everything around finding and readying evidence for lab work and presentation in court.

Categories of Evidence (foundational ideas)

• Testimonial evidence

  • Definition: Testimony about what a person saw, heard, or knows; essentially verbal accounts from witnesses or involved parties.

  • Role: A cornerstone of criminal prosecutions; often drives cases even though it is not scientific.

  • Real-world note: People can be unreliable witnesses or biased, yet testimonial evidence is generally accepted as valid.

• Documentary evidence

  • Definition: Evidence that exists in documents or records (e.g., attendance sheets, birth certificates, deeds, court records).

  • Example: A class attendance sheet showing who was present on a specific date can supplement or corroborate testimony.

  • Significance: Documents can support or counter testimonial recollections when memory is imperfect.

• Demonstrative evidence

  • Definition: Helpful illustrations that clarify facts but are not themselves direct records or testimony.

  • Examples: Diagrams of a house, maps, blueprints, or a weighted representation of a tool (e.g., a baseball bat’s impact characteristics) used to illustrate a point.

  • Function: Aids the finder of fact (jury) in understanding complex information.

  • Note: Demonstrative evidence is not the actual object or event but a representation of it.

• Physical evidence

  • Definition: Tangible objects that can be touched and handled; can range from microscopic samples to large items.

  • Subtypes: Direct evidence and indirect evidence; circumstantial evidence falls under indirect evidence in many cases.

  • Importance: Physical evidence is the core of most forensic investigations and lab analyses.

Direct vs Indirect vs Circumstantial Evidence

• Direct evidence

  • Definition: Proves the fact in question without needing additional inference (e.g., a video showing a person committing an act).

  • Example: A video recording of someone striking another person.

• Indirect evidence

  • Definition: Tends to incriminate or exculpate but does not on its own prove the fact beyond a reasonable doubt.

  • Example: A security hallway video showing a suspect exiting near the time of the incident; the video does not show the act itself but suggests possible involvement.

• Circumstantial evidence

  • Definition: A category of indirect evidence that, taken together with other evidence, can support guilt beyond a reasonable doubt.

  • Key point: In the justice system, circumstantial evidence can be as dispositive as direct evidence when sufficient evidence is presented.

  • Example: A witness testifies to seeing a person run from the scene; other corroborating evidence links the suspect to the location.

• Associative evidence

  • Definition: Evidence that links a suspect to a location or object (e.g., fingerprints, DNA at a scene).

  • Strength varies: Can be powerful but is not always probative (depends on context and the totality of evidence).

  • Caveat: Presence at a location does not by itself prove guilt.

• Probative vs competent evidence

  • Probative evidence: Tends to prove guilt or innocence; evaluated for its quality and relevance.

  • Competent evidence: Evidence that is legally admissible and properly collected/secured; must meet standards of value to be usable in court.

Key Terms and Concepts in Forensic Evidence

• Trace evidence

  • Definition: Extremely small physical evidence (e.g., fibers, hair, pollen, dust) that leaves a trail and requires careful analysis.

  • Significance: Can provide important links between a suspect, victim, and crime scene when larger items are not available.

• Prima facie evidence

  • Definition: Evidence that, on its own, would be sufficient to prove guilt or a key element of a crime under a statute.

  • Reality: In most cases, few or no instances of prima facie evidence exist; guilt beyond a reasonable doubt usually requires a compelling collection and presentation of multiple types of evidence.

  • Example: A statutory blood alcohol content (BAC) threshold such as BAC = 0.08 may constitute prima facie evidence in certain DUI contexts, though the overall case still requires proper proof.

• Associative evidence

  • You can be linked to a crime scene by items or data found at the scene (e.g., fingerprints, DNA, hair).

  • Limitation: Associative evidence alone may not prove guilt; context matters.

• Probative value

  • Definition: The capacity of evidence to prove something important in a case.

  • Assessment: Courts weigh how much a piece of evidence tends to prove guilt or innocence relative to other evidence.

• Competent evidence

  • Definition: Evidence that is legally admissible and collected in a proper way, meeting standards of reliability and relevance.

  • Dependency: Competence often hinges on how evidence was collected, identified, and secured (chain of custody).

Examples and Illustrative Scenarios from the Transcript

• Identifying evidence beyond discovery

  • Scenario: Finding a shard of bone in the wilderness prompts questions about whether it is human bone or animal bone, illustrating the need to identify the material before analysis.

• Demonstrative vs real evidence in court

  • Demonstrative example: A baseball bat used in a crime is not the actual impact instrument but a demonstration of what the force might have been like; a demonstration can help juries understand the context.

  • Real evidence: The actual physical object (the bat) remains in evidence and may be subjected to lab analysis.

• The Herbert murder case (indirect evidence in a real homicide)

  • Facts: A mother dies in a mobile-home fire; authorities find marks on the body suggesting prior strangulation; the suspect claims to have woken to walk the dog; later, investigators question him and a fire marshal finds accelerant start points.

  • Indirect/ circumstantial chain: The suspect’s actions and the lack of direct evidence linking him to the murder (e.g., no one else seen) build a case through indirect evidence.

  • Outcome: The suspect is convicted based on circumstantial evidence (indirect evidence) rather than a direct confession or direct proof of the murder itself.

• The purse theft case and the CSI effect in play

  • Scenario: A woman is caught on video stealing a purse; defense argues that there is no DNA or fingerprints on the purse in court.

  • Lesson: Jurors often expect scientific evidence (DNA, fingerprints, ballistics) even when not directly applicable; this illustrates the CSI effect and the demand for forensic data that may not exist in many cases.

• The “paint transfer” example in a DUI-like scenario

  • Scenario: A suspect’s car paint matches paint at the crime scene; jurors expect significant forensic paint analysis data, and the lack of a full molecular paint comparison undermines the prosecution’s case.

  • Lesson: Jurors may demand highly specific scientific evidence (e.g., molecular-level paint transfer data) that was not available, influencing verdicts despite circumstantial evidence.

• The role of DNA in cases and the danger of contamination

  • Anecdote: A crime lab employee’s contamination led to false associations of DNA across multiple cases; highlights the importance of preventing cross-contamination and maintaining rigorous laboratory controls.

• The gender-based/victim-focused implication of DNA evidence collection

  • Issue: Victims of rape may be reluctant to preserve DNA evidence if they choose to shower or clean themselves, which can destroy crucial forensic material and reduce the ability to obtain DNA evidence.

Forensic Science: What It Is and What It Is Not (CSI effect and tech effect)

• Forensic science definition

  • Application: The use of natural sciences (biology, chemistry, physics, and related fields) to gather, analyze, and interpret physical evidence for legal purposes.

  • Strengths: Helps identify suspects, narrow down possibilities, and provide objective data to support investigations.

  • Limitations: Not infallible; results depend on collection, handling, interpretation, and context; not all cases yield a full set of scientific data.

• The CSI effect

  • Definition: A cultural phenomenon where Hollywood portrayals glamorize forensic science and create unrealistic expectations about the availability, speed, and certainty of scientific evidence in real cases.

  • Consequences: Jurors may demand DNA, ballistics, or other advanced testing in cases where such evidence is not applicable, available, or necessary.

  • Statistics and perceptions highlighted in the lecture:

  • Approximately 42\% of jurors expect DNA to be present in every case.

  • Approximately 56\% expect fingerprint evidence in every case.

  • Approximately 49\% expect ballistics in every gun-related crime.

  • A notable portion of jurors also expect to see other sophisticated forensic evidence, influenced by media portrayals.

  • The tech effect (a related concept): Public awareness of modern technology and capabilities can further shape jurors’ expectations, sometimes driven by popular media depictions (e.g., “Jason Bourne”-style hacking or instant digital analyses).

  • Real-world impact: These expectations can influence trial strategy, evidence presentation, and juror decision-making; professionals must manage expectations and explain limitations where appropriate.

• Practical implications for investigators and students

  • Realistic expectations vs. media portrayals: Recognize that forensic science is powerful but not omnipotent; evidence must be appropriate to the case and collected properly.

  • Training and communication: When presenting evidence, explain the scope, limitations, and significance in plain terms to ensure jurors understand the strength and uncertainties of forensic data.

  • Ethical and professional responsibilities: Avoid overstating findings; maintain rigorous chain of custody and lab quality controls to prevent contamination or misinterpretation.

Practical Takeaways for Investigators and Students

• Always think in terms of categories and how each category contributes to the whole case:

  • Testimonial: Reliability, memory limitations, bias, and corroboration needs.

  • Documentary: Authenticity, records management, and corroboration of memory.

  • Demonstrative: Clarity for the finder of fact; ensure it accurately reflects the underlying facts.

  • Physical: Direct vs indirect vs circumstantial; validate through corroboration, chain of custody, and lab analyses.

• Understand the strength and limits of different evidence types:

  • Direct evidence provides strong, straightforward proof when genuine (e.g., video). It is rarely the sole basis for a conviction.

  • Circumstantial evidence can be decisive when multiple strands fit together—jury decisions hinge on the totality of the evidence.

  • Associative evidence links a person to a scene or object but must be contextualized to assess guilt.

  • Trace evidence, while small, can be highly probative when properly analyzed and matched.

• Remember the chain of custody and evidence handling principles:

  • Proper collection, labeling, storage, and transport.

  • Avoid contamination; track all who handle evidence and maintain documentation.

  • Secure storage until analysis and court presentation.

• Be mindful of the CSI and tech effects in real trials:

  • Do not overstate findings; acknowledge limitations.

  • When DNA or other high-stakes forensic results are absent, use strong non-forensic evidence to build a credible case.

  • Prepare jurors for the realities of forensic science, including the fact that not every case yields DNA, fingerprints, or ballistic data.

• Foundational math and data points to remember

  • Blood Alcohol Content threshold in many jurisdictions: BAC = 0.08 (example of prima facie legal standard in DUI contexts).

  • The CSI effect has been a public cultural factor for roughly 25\text{ years}, shaping expectations in modern trials.

  • Juror expectation statistics from the lecture: roughly 42\% expect DNA in every case, 56\% expect fingerprint evidence, and 49\% expect ballistics in gun-related cases.

Connections to Foundational Principles in Law and Science

• Burden of proof: Beyond a reasonable doubt remains the standard; evidence must collectively meet this standard, not merely exist.

• The role of credibility: Eyewitness testimony, documentary records, and the reliability of forensic analyses all contribute to the finder of fact’s assessment.

• The interplay between science and law: Forensic science shapes investigative decisions and courtroom outcomes, but it must be applied correctly and communicated transparently.

Final Reflections

• For investigators and students, the key is to integrate multiple forms of evidence, understand their strengths and limitations, and communicate clearly to avoid the pitfalls of the CSI effect.

• Ethical practice requires rigorous collection, careful interpretation, and honesty about what the evidence can and cannot prove.

• The goal is to use science to illuminate truth while acknowledging human factors, uncertainties, and the standards of the legal system.