forensic science test 1

what is the type of witness allowed to give their opinion on the case

Expert witness

what is the standard where scientific teqniques must be accepted by experts in the field

frye standard

physical evidence that narrows down a source to a group of items

class evidence

physical evidence that could be linked to one source

individual source

Forensic Science

The application of scientific methods and principles to answer legal questions ("science in service of the law").

Locard’s Exchange Principle:

"Every contact leaves a trace." Whenever two objects or people come into contact, a cross-transfer of physical material occurs.

Expert Witness:

A specialist permitted to state professional opinions and conclusions in court based on specialized training and scientific analysis.

Fact Witness:

A witness who can only testify about what they directly saw, heard, or experienced (cannot give scientific opinions).

CSI Effect:

The phenomenon where popular TV shows cause jurors to have unrealistically high expectations for rapid, high-tech, perfect scientific proof in every trial.

Frye Standard

Scientific techniques/evidence must be "generally accepted" by experts in the relevant field.(1923)

Daubert Standard

The judge acts as a "gatekeeper" and checks testability, peer review, error rates, and general acceptance. (1993)

Class Evidence

Physical evidence that narrows down a source to a group or category of items (e.g., shoe tread pattern common to a sneaker model, blood type A, red cotton shirt fibers, car paint batch)

Individual Evidence:

Physical evidence that can be linked to a single, unique source to the exclusion of all others (e.g., full DNA profile, unique latent fingerprint, matching broken glass fracture edges).

Discrete Data:

Data with a limited, countable set of distinct outcomes (e.g., blood type, coin flips).

Continuous Data:

Data measured along a continuous scale with infinite potential numeric values (e.g., length of a bone, drug purity percentage, refractive index of glass).

Contextual / Confirmation Bias:

When an investigator or analyst allows outside information (like police reports or expectations) to bias or influence how they interpret evidence.

Control / Background Sample:

An uncontaminated sample taken from near an evidentiary stain to confirm that the background surface/substrate does not interfere with chemical test results.

CODIS (Combined DNA Index System)

National database used to compare and match DNA profiles across federal, state, and local labs.

IAFIS / NGI

FBI biometric system used to search and match fingerprints.

NIBIN

National database used to compare ballistic evidence (fired bullets and cartridge casings).

First Responder Duties

1. Render medical aid to injured individuals (life safety always comes before evidence).

2. Secure and isolate the crime scene (establish perimeters, establish a scene log, block unauthorized entry).

1. Notes

Detailed, written records made at the scene recording arrival times, environmental conditions, and actions taken.

2. Photography / Video

Captures overall, mid-range, and close-up views (both with and without scales) before anything is moved.

3. Sketching

Shows exact spatial relationships, room layout, and measured distances from fixed reference points

Line / Strip Search:

Searchers walk parallel straight lines across large or outdoor areas.

Grid Search:

Two overlapping perpendicular line searches (most thorough coverage).

Zone Search:

Scene is divided into sections/quadrants, searched independently (great for large buildings or multi-room scenes).

Spiral Search

Searcher moves in a spiral pattern in or out from a central point (good for open fields).

Biological Evidence (Blood, Saliva, Wet Swabs):

Must be air-dried and stored in breathable paper packaging (paper bags, envelopes). NEVER store in sealed plastic, as trapped moisture causes mold growth and destroys DNA!

Trace & Fragile Evidence (Glass, Metals, Powders)

Packaged in rigid containers (small boxes, plastic canisters, padded envelopes) to prevent puncturing or breakage.

Chain of Custody

A continuous, written record log showing every person who collected, transferred, handled, or analyzed a piece of evidence. If the chain is broken, evidence may be excluded from court!