Introduction to Forensics

Adjudicated

Settled; a decision is made

Bias

Factors that can influence a criminal investigator’s judgement

Burden of Proof

The prosecutor must prove a defendant guilty beyond a reasonable doubt (must provide evidence)

Civil Law

Cases between individuals or parties (lawsuit or being sued)

Criminal Law

Involve government as the body that is charging

Defendant

Who is accused

Felony

A more serious criminal case

Jurisdiction

Region or geographical area over which law enforcement or legal entity can exercise authority

Misdemeanor

A less serious criminal case

Plaintiff

The party who initiates a civil lawsuit (usual civil law but sometimes criminal law)

Plea Bargaining

Defendant agrees to plead guilty in order to get a shorter sentence

Probable Cause

Legal standard requiring evidence for an officer to believe a crime happened

Prosection

The party that files criminal charges

Trier of Fact

Judge or jury who will make the decision based on the evidence presented

Abductive reasoning

Most commonly used in criminal investigations, based on gathering what is known and using this information to come up with the simplest and most likely explanation

Admissibility

Whether eyewitness testimony, photographs, physical objects, or scientifically generated information such as DNA is legally acceptable for presentation in court

Circumstantial evidence

Basis from which additional information can be inferred (indirect evidence)

Daubert standard

Ensures that the judge is the gatekeeper and that expert testimony is relevant and reliable (not generally accepted by science community like the Frye standard)

Daubert trilogy

Three cases: G.E. v Joiner, Kumho Tire v Carmichael, and the Daubert decision

Deductive reasoning

Using evidence, principles, and logic to come to a conclusion. Compared to algebra and mathematical reasoning. In forensics, it can come from DNA typing. Also referred to as inference

Direct evidence

Information that establishes directly, without the need for further inference, the fact for which the information is offered (eyewitness, video footage)

Exclusive evidence

Excludes a person as a source as the evidence does not match up to them

Exculpatory evidence

any forensic evidence, such as DNA or digital data, that points to a defendant's innocence or creates reasonable doubt about their guilt

Federal Rules of Evidence

Govern what evidence can be presented in U.S. federal civil and criminal trials, aiming to ensure fairness, accuracy, and efficiency in the judicial process

Frye standard

Based on the court case Frye v United States, requires scientific methods to be generally acceptable to a significant proportion of the scientific discipline to which they belong

Inclusive evidence

Includes a person as a source (connected to evidence)

Inculpatory evidence

Evidence that proves a person’s guilt

Inductive reasoning

Uses existing data to make predictions and generalizations

Locard’s exchange principle

Contact or interaction between people or between a person and a place inevitably produces some type of exchange of material between them that is evidence of the interaction

Opinion evidence

Where a forensic scientist offers his or her opinion as part of the body of evidence that is considered in any given case

Physical evidence

Raw material needed by forensics scientists (impressions, guns, fingerprints)

Rules of evidence

Rules designed to ensure that only reliable and relevant scientific information is considered by the court. Admissibility or inadmissibility of trial information is determined by the trial court’s application of the rules of evidence

Testimonial evidence

People other than the suspect or the victim may be present and can act as witnesses (AKA eyewitness evidence)

Transfer evidence

An exchange of material between people or between a person and a place

Case Manager

Assigned to oversee and collect analyses and assist in collecting the information that comes from the analysts

Chain of Custody

Documentation of the found items (before any evidence can be moved or collected)

Control Samples

Samples that are not thought to be related to the event in question but necessary for proper interpretation of evidence collected

Crime Scene Map

Use of imaging technology and GPS to create a 3D map of crime scene

Crime Scene Reconstruction

Done to test competing hypotheses proposed to explain the physical evidence. Evidence and reconstruction must be internally consistent

Elimination Samples

Collected from people who enter the scene as part of the investigation (ex: fingerprints, DNA)

First Responder

Police, fire services, ambulances who provide medical assistance to the victim, which starts with checking for vital signs

Forensic Mapping

Practice of recording scenes using crime scene maps

Macroscopic Crime Scene (Macroscene)

Large scale of a scene (ex: house or lot)

Microscopic Crime Scene (Microscene)

Smaller parts of a scene (ex: room). Could be room in which the initial assault took place

Primary Container

Most items of evidence at crime scene are packaged in here

Primary Crime Scene

Where the initial crime act occurred (ex: house where wife was shot)

Secondary Container

Primary container placed in secondary container

Secondary Scene

Created by acts that follow the original scene (ex: burial site or truck)

Walk-Through

Investigators survey area to see how much must be secured and photos/videos are taken

Forensics

The application of scientific methods and techniques to investigate crimes and examine evidence for use in court

Difference between criminal law and civil law

Criminal law deals with actions considered harmful to society (e.g., murder, theft). Civil law deals with disputes between individuals/organizations (e.g., contracts, property, divorce).

Federal Rules of Evidence (FRE)

A set of rules that govern what evidence is admissible in federal courts, ensuring trials are fair, consistent, and reliable.

Why FRE are exclusionary

Because they exclude evidence that is irrelevant, unreliable, unfairly prejudicial, or illegally obtained. This protects fairness in court.

Admissible

Evidence that is legally allowed to be presented and considered in court.

Frye admissibility standard

 Scientific evidence is admissible if the methodology or principle is generally accepted by the relevant scientific community.

Daubert admissibility standard

 The judge decides if scientific evidence is reliable and relevant, considering factors like peer review, testing, error rates, and general acceptance.

Key differences between Frye and Daubert

Frye: Based only on general acceptance in the scientific community. Daubert: Broader test; judge acts as “gatekeeper” considering reliability, testing, peer review, error rate, and acceptance.

Role of the judge

Acts as an impartial authority, rules on admissibility of evidence, ensures fair procedures, instructs the jury on the law, and may determine verdicts in bench trials.

Bill of Rights

4th–8th Amendments in criminal proceedings –

4th: Protects against unreasonable searches/seizures (requires warrants/probable cause).

5th: Protects against self-incrimination, double jeopardy, guarantees due process.

6th: Guarantees fair and speedy trial, right to counsel, and right to confront witnesses.

7th: Right to a jury trial in civil cases.

8th: Protects against cruel/unusual punishment and excessive bail.

Role of the prosecution

Represents the government; presents evidence to prove the defendant’s guilt beyond a reasonable doubt.

Burden of proof

The responsibility of the prosecution to prove the defendant’s guilt; in criminal trials it is beyond a reasonable doubt.

Role of the defense

Protects the defendant’s rights, challenges prosecution evidence, and presents alternative explanations.

Reasonable doubt

The standard of proof; if the jury has any reasonable uncertainty about guilt, they must acquit.

Exculpatory vs. inculpatory evidence

Exculpatory: Favors the defendant, suggesting innocence. Inculpatory: Suggests the defendant’s guilt.

Why “not guilty” ≠ innocent

 A verdict of “not guilty” only means the prosecution failed to prove guilt beyond a reasonable doubt, not that the defendant is proven innocent.

Failures of visual awareness

When people fail to notice important visual details or changes in their environment.

Inattentional blindness

Failure to notice something visible because attention is focused elsewhere.

Change blindness

Failure to detect a visual change in a scene.

Testimonial evidence

 Statements made under oath (e.g., witness testimony).

Why eyewitness testimony is unreliable

Memory is flawed; stress, suggestion, or bias can distort recall, making eyewitness accounts prone to error.

Locard’s Exchange Principle

 “Every contact leaves a trace.” When two objects/people come into contact, material is transferred.

How physical evidence relates to Locard

 Any trace (hair, fibers, fingerprints) found at a scene shows an exchange between suspect, victim, and environment.

Trace evidence

 Small amounts of material left behind (e.g., hair, fibers, soil, gunshot residue).

Direct evidence

Directly proves a fact (e.g., video of a crime, eyewitness statement).

Indirect (circumstantial) evidence

Suggests a fact through inference (e.g., fingerprints at a crime scene).

Difference in direct and indirect

Direct = proves fact outright; Indirect = requires inference.

Physical evidence

Any tangible item collected from a crime scene (weapons, fingerprints).

Biological evidence

Subset of physical evidence that comes from living organisms (blood, saliva, DNA, hair).

Class evidence

 Links to a group/category, not an individual (e.g., shoe size, car paint).

Individual evidence

Uniquely identifies a person or object (e.g., DNA, fingerprints).

Importance of scale drawing

Provides accurate, permanent documentation of the crime scene for investigations and trials.

Grid

Double-line search; best for large areas.

Linear/Line

Straight lines; good for large, open areas.

Quadrant/Zone

Scene divided into zones; good for houses/buildings.

Spiral

Start at center and move outward or vice versa; good for small areas.

Seven S’s of CSI

Secure the scene

Separate witnesses

Scan the scene

See the scene (photograph)

Sketch the scene

Search for evidence

Secure and collect evidence

Seven S’s explained

Secure: Ensure safety, preserve evidence.

Separate: Prevent collusion.

Scan: Determine primary/secondary crime scene.

See: Take photos/videos.

Sketch: Create rough sketch.

Search: Use search patterns.

Secure/collect: Properly bag, tag, and maintain chain of custody.

Primary crime scene

where crime occured

Secondary crime scene

Related locations (ex: body dumped somewhere)

Chain of custody

The documented record of who collected, handled, transferred, and stored evidence to maintain integrity.