1. Introduction to Forensic Science and the Law
Federal Rules of Evidence
In order for scientific evidence to be admitted in a court of law, it must be:
a) Probative: actually proves something
b) Material: addresses an issue that is relevant to the particular crime

2. Introduction to Forensic Science and the Law
Admissibility of Evidence
The Frye Standard
From the 1923 case Frye v. United States
Standard used for determining if scientific evidence may be presented before the court.
The standard states that the court will accept expert testimony on “well recognized scientific principle and discovery’ if it has been “sufficiently established and has received general acceptance” in the scientific community

3. Introduction to Forensic Science and the Law
Admissibility of Evidence
The Daubert Ruling
From the 1993 case Daubert v. Merrell Dow pharmaceuticals
The judge may use expert testimony to “understand evidence” and decide if the evidence can be entered into the trial. Admissibility of new scientific technique or theory is determined by:
be subject to testing and peer review
Be standardized with recognized maintenance of such standards
Have a known and accepted error rate
Attain widespread acceptance

4. Introduction to Forensic Science and the Law
Using Evidence
Evidence is used to:
determine if a crime has been committed
link a suspect to a crime scene
corroborate or refute an alibi or statement
identify a perpetrator or victim
exonerate the innocent
Induce confession
Direct further investigation

5. Introduction to Forensic Science and the Law
Using Evidence
Crime scene evidence is valued for the following:
Corpus Delicti-Latin term which means “the body of the crime” or the essential facts of the crime. Evidence will reveal exactly what type of crime was committed
Modus operandi (MO)-The steps and method (usually repetitive) the perpetrator employed to commit the crime

6. Introduction to Forensic Science and the Law
Using Evidence
Crime scene evidence is valued for the following:
Linkage-association, or linking of a suspect to a crime scene, or victim
Verification-substantiate or refute suspect or witness statement
Suspect Identification-evidence such as fingerprint and DNA can often identify the perpetrator

7. Introduction to Forensic Science and the Law
Using Evidence
Increasing the value of class evidence involves:
Finding as many different items as possible with which to link the suspect to the crime or victim
Use the product rule (statistical analysis) to narrow down your pool of suspect so that the probability of all those pieces of evidence identifying someone else as the perpetrator of the crime is almost impossible.

8. Introduction to Forensic Science and the Law
Analysis of Evidence
Crime scene evidence is analyzed for two reasons:
Identification: determines exactly what a particular item or substance is.
Comparisons: done to see if suspected items share a common origin or source (did they come from the same person, place, or object).

9. Introduction to Forensic Science and the Law
Analysis of Evidence
Evidence that is being analyzed may exhibit:
Class characteristics-not unique to a particular object, but can be narrowed down to a specific group
Individual Characteristics-unique, can be narrowed to single source to make direct connection (DNA, Fingeprint)

10. Introduction to Forensic Science and the Law
Analysis of Evidence
Class evidence can be individualized.
Individualizing the evidence eliminates everyone except the perpetrator.
Evidence is intended to eliminate suspects rather than point the finger at any one person