Intro to Forensic Science

Forensic Science

• Science applied to matters of law

• Establishes the facts of the crime - who, when, where, what, why, how

• Corroborates (verifies) the accuracy of testimonial evidence

• May be able to confirm what something is, but now always how it came to be there

Criminal Law vs. Civil Law

• Criminal Law

  • Regulates society as a whole (government represents society)

  • Suit initiated by prosecution

  • Penalties: jail, parole, probation, prison, community service, house arrest, fines

  • The prosecutor must prove guilt beyond a reasonable doubt

  • Cases: murder, terrorism, robbery, assault, kidnapping, battery

• Civil Law

  • Regulates disputes between individuals and/or companies

  • Suit initiated by plaintiff

  • Penalties: fines/restitution/remediation, punitive damages/punishment

  • The plaintiff must prove by the preponderance of the evidence (that it’s more likely than not) and defendant will be found liable

  • Cases: fraud, divorce, money laundering, child custody, embezzlement, car collision

Physical vs. Testimonial Evidence

• Physical Evidence: Tangible material that can assist the trier of fact in understanding events in question and relationship of people to events in question

• Testimonial Evidence: A statement made by a witness, either orally or in writing, that is presented in court as proof of a claim

Sources of inaccuracy/vulnerability in testimonial evidence

• People are not reliable recorders/reporters of events because the brain is constructive, adding and changing details, and many of those details are filtered through our own personal experiences and biases

• Stress, medical conditions, medications, drugs, trauma, lying, and word choice of investigators can influence testimony 

Unknown vs. Known samples

• Unknown (questioned/crime scene)

  • Items that were “happened upon” in the process of investigating the event

  • Their origin is not clear or certain or proven

  • Ex. blood, shoe print, hair strands

• Known (reference/standard/control)

  • Item collected/sought out/looked up on purpose from its original source, in order to compare the unknown back to it to establish the origin of the unknown

  • Ex. DNA swab from original source

Locard Exchange Principle

• Every contact leaves a trace 

• Establishes linkage

7 ways that Physical Evidence can be used

• Identify - What is it?

  • Compare back to a known reference library of drug chemicals and formulations

• Comparison - From where did the material originate?

  • Put 2 samples (usually a known and an unknown) side by side to compare their features/molecules present and absent, quantities of molecules, location/position 

  • Can result in Dissociation, Individualization, Classification

• Linkage - Evidence that shows 2 items were in contact with one another

  • Based on the Locard Exchange Principle

• Corroborate - Testimonial evidence of a witness, victim, suspect

  • Can verify/support or refute/disprove claims

• Reconstruct/Reenact - How did the events take place? Where? What position? When? In what order?

  • Ex. GPS history, camera footage, blood spatter, blood trajectories

• Establish M.O. - How a crime is committed/mode of operations

  • Most useful for repeated crimes

  • Useful to warn the public or link seemingly unrelated crimes

• Investigative Lead - Last resort of what to do it evidence and shows who/where to go next for more information

Individualization vs. Classification

• Individualization: As close to 100% certain as a scientist would ever say, that the 2 samples almost definitely did come from the same origin/source

  • DNA, unique tool marks

• Classification: It is possible, but not certain, that the 2 samples came from the same origin/source; this source can’t be ruled out as a possibility

  • It can narrow down to a specific group of people or smaller subset of possibilities

  • Shed hair, blood type, shoe print, any manufactured product

Disassociation

• These 2 samples (a known and unknown) could not have come from the same origin

• Can rule out suspects and saves time, money, and resources

Jigsaw Fit

• Can be used to individualize paper, clothing, glass, egg shells

Why scientists do not use “match”

• “Match” assumes individualization

Legal Precedent

• Legal standard/what has been decided in the past

Frye v. United States

• Defendant takes and passes a polygraph test claiming innocence but trial court excludes this from being admitted

• Defendant is convicted and appeals the conviction

• The Court of Appeals of the District of Columbia upholds the ruling

  • Scientific evidence must be “sufficiently established to have gained general acceptance in the particular field in which it belongs” to be admitted into court

Daubert v. Merrell

• It was alleged that a drug used to treat morning sickness, Bendectin, was causing birth defects (it was acting as a teratogen)

• The manufacturer of the drug (defendant) presented an expert witness who said none of existing scientific literature supported a cause-effect relationship

• Plaintiffs presented other expert witnesses who cited non-published/non-peer reviewed data and new analyses of previously published data to support a cause-effect relationship

• Lower court ruled plaintiff evidence inadmissible

• Daubert appealed to the Supreme Court 

• Supreme Court upheld the ruling but laid out the Daubert Standard

Daubert Standard

• Evidence must be relevant to the case

• The judge is the gatekeeper of what evidence is allowed in or not

• Evidence must be grounded in scientific knowledge, gained through reliable methods:

  • Tested technique, verifiable by others

  • Peer-reviewed/published

  • Known or potential error rate

  • Standardized protocol/threshold for conclusions

  • Widespread acceptance (Frye)

General Electric Co. v. Joiner

• Joiner was an electrician and developed lung cancer and claimed his exposure to chemicals increased risk

• Plaintiff’s expert witness attempt to use data from animal models to show exposure increased risk of cancer in humans

• Lower court ruled plaintiff’s evidence inadmissible

  • District court reversed it

• Court may limit the extrapolation from a legitimate set of data

Kumho Tire Co. v. Carmichael

• Carmichael sued Kumho when a tire blew out and killed 1 person and injured more

• Plaintiff’s expert witness confirmed the blow out was a result of a defect

• Court ruled this evidence inadmissible because his methodology didn’t meet the Daubert standard

• Confirmed that people with technological expertise/experience can serve as an expert witness, but methods they use must still meet the Daubert Standard

Melendez-Diaz v. Massachusetts

• Police caught Melendez-Diaz selling drugs and searched his car

• He was convicted of drug trafficking

• Certificates of chemical analysis were submitted that said the substance was a drug, but analyst didn’t appear in court

• Defendant appealed, saying he had the right to confront his accuser

• Supreme Court ruled that analysts are compelled to appear in court before the defendant to represent their results

  • Didn’t apply to Melendez-Diaz or any cases before it though!

Graphology vs. Handwriting Comparison

• Graphology: The study of handwriting to interpret personality traits

• Handwriting Comparison: Used to compare writing samples to determine who wrote something

• Both very unreliable!!!

  • But handwriting comparison is still allowed to be admitted into evidence in some places

Deductive vs. Inductive/Empirical reasoning

• Deductive Reasoning: Using a known principle (e.g., "all suspects with this DNA are excluded") to reach a certain conclusion about a specific suspect

  • General → Specific

• Inductive/Empirical Reasoning: Observing multiple similar crime scenes to form a broader theory that a single person committed them

  • Specific → General