Chapter 1 - Introduction to Forensic Science
1. What is forensic science? (Start here)
Forensic science is the application of scientific methods to legal questions, especially criminal investigations.
In simple terms:
Forensic science helps answer who, what, when, where, how, and sometimes why in a crime.
It sits at the intersection of:
Science (biology, chemistry, physics)
Law
Criminal justice
⚠ Important exam point:
Forensic science does NOT solve crimes on its own — it supports investigations with scientific evidence.
2. What forensic scientists actually do
A forensic scientist:
Examines physical evidence
Uses validated scientific techniques
Produces objective results
Testifies in court as an expert witness
They are NOT:
Detectives
Prosecutors
People who decide guilt or innocence
Think this way for exams:
Investigators collect evidence → forensic scientists analyze it → courts interpret it.
3. Types of forensic evidence
Physical Evidence
Anything tangible that can link:
A suspect to a victim
A suspect to a scene
A victim to a scene
Examples:
Blood
Hair
Fibers
Fingerprints
Weapons
Documents
🔹 Class vs Individual Evidence (VERY IMPORTANT)
Class evidence
Narrows things down to a group
Cannot identify one unique source
Examples:
Blood type
Shoe size
Fiber type
Individual evidence
Can be linked to one single source
Much stronger in court
Examples:
DNA
Fingerprints
Toolmarks (sometimes)
📌 Midterm tip:
If you see a question asking “Which is stronger?” → Individual evidence
4. The forensic science process (step-by-step)
Recognition – noticing evidence exists
Documentation – photos, notes, sketches
Collection – careful, controlled gathering
Preservation – prevent contamination
Analysis – lab testing
Interpretation – what does it mean?
Presentation – court testimony
⚠ Chain of custody begins the moment evidence is collected
5. Popular culture vs real forensic science
TV shows (CSI effect) make forensic science look:
Fast
Perfect
Always conclusive
Reality:
Takes time
Has limitations
Results can be probabilistic, not absolute
Exam mindset:
Courts rely on science — but science is never 100% certain.
Key Terms and Concepts.
Accreditation
Official approval that a lab or institution meets set standards.
Think: “This lab has been checked and approved.”
Certification
Proof that an individual (not a lab) is trained and qualified.
Accreditation = lab
Certification = person
Bias
When personal beliefs or expectations affect objectivity.
Bias can make someone “see what they expect to see.”
Contextual information
Extra details about a case that aren’t needed for testing, but can influence results.
Example: Knowing a suspect already confessed.
Falsifiability
A claim must be testable and able to be proven wrong to be scientific.
If it can’t be tested, it’s not real science.
Internally consistent
Results make sense within the same test or system.
No contradictions in the findings.
Junk science
Methods that look scientific but aren’t reliable or valid.
Often used improperly in court.
Pseudoscience
Fake or unproven science that pretends to be real science.
Astrology = pseudoscience
DNA analysis = real science
Reproducibility
Other scientists can repeat the test and get similar results.
If it can’t be repeated, it’s unreliable.
Self-correction
Science improves over time by finding and fixing mistakes.
Science evolves — it’s not perfect.
Peer review
Experts check and critique research before it’s published.
Quality control for science.
Blank
A test sample with no substance used to check contamination.
“Nothing should show up here.”
Blind sample
A sample tested without the analyst knowing what it is.
Prevents bias.
Double-blind sample
Neither the analyst nor the supervisor knows what the sample is.
Strongest protection against bias.
Known
A sample whose source is already known, used for comparison.
Example: a suspect’s fingerprint.
Negative control
A test that should produce no reaction.
If something appears, something went wrong.
Positive control
A test that must produce a known result.
Confirms the test is working.
Quality assurance / quality control (QA/QC)
Steps taken to ensure accuracy, consistency, and reliability.
Rules that prevent mistakes in labs.
Sequential unmasking
Giving examiners information step by step, only when needed.
Reduces bias by limiting unnecessary context.
Standard operating procedure (SOP)
A written step-by-step method for doing tests the same way every time.
No guessing, no shortcuts.
⚖ LEGAL SYSTEM & COURT TERMS
Adjudicated
A case that has been officially decided by a court.
The judge or jury reached a decision.
Adversarial system
Legal system where two opposing sides argue their case.
Prosecution vs defense.
Burden of proof
Who must prove the case.
In criminal cases: the prosecution.
Civil law
Deals with private disputes, not crimes.
Example: lawsuits, money damages.
Criminal law
Deals with crimes against the state.
Punishment can include jail or fines.
Defendant
The person accused of a crime or wrongdoing.
Plaintiff
The person who brings a case in civil court.
Prosecution
The legal team that represents the state in criminal cases.
Prosecutorial bias
When prosecutors push too hard for a conviction, ignoring fairness.
This can pressure forensic scientists.
Plea bargain
An agreement where the defendant pleads guilty for a lesser charge or sentence.
Saves time, avoids trial.
Precedent
A past court decision used to guide future cases.
Courts look to history.
Probable cause
Reasonable grounds to believe a crime occurred.
Needed for arrests or warrants.
Jurisdiction
The legal authority to hear a case.
Depends on location and type of crime.
Felony
A serious crime with harsh punishment.
Example: murder, robbery.
Misdemeanor
A less serious crime.
Example: minor theft, disorderly conduct.
Trier of fact
The person who decides what actually happened.
Judge or jury.