Evidence and Expert Testimony

Expert Testimony  Two Types of Witnesses: Fact and Expert  Fact -- have personal knowledge of facts of case  Cannot give opinion on what happened  Expert -- can give opinion  Allows jury to understand something technical that they would not otherwise understand  Forensic scientist:  Acts as scientist in analyzing evidence  Acts as expert witness

Expert Testimony  Judge is a “gatekeeper” -- decides when expert testimony is necessary  Basic issue: Is the evidence relevant and reliable?  Standards that the judge applies:  Old standard: “Frye” Test (1923)  Procedure underlying expert testimony must be “generally accepted by the scientific community.”  New standard: “Daubert” Test -- much broader  “Generally accepted” is only one factor  Has the technique been tested?  Has the technique been subject to peer review or publication?  Are there known or potential error rates?  Are there standards that control how technique is done?

Expert Testimony  Federal Rules of Evidence: Rule 702  Governs testimony by expert witnesses  Expert must be qualified by his or her “knowledge, skill, experience, training or education”  Don’t need to be a scientist  Have to base the testimony on “sufficient facts and data”

Evidence  Evidence is ANYTHING that has “probative” value  Probative = proves a fact  FRE 401: Evidence must be relevant  Is “of consequence” in determining action  Makes a fact “more or less probable”

Evidence  Direct vs. Circumstantial  Direct: proves a fact without any other inferences or conclusions in the middle  Mary saw John stab Sue.  John’s fingerprint is on the knife.  Circumstantial: needs middle inference or conclusion to link it to crime  Mary sees John run away from Sue and finds Sue stabbed.

Forms of Evidence  Witness Testimony (testimonial)  Physical Evidence  ANYTHING that shows crime committed or links crime to either victim or perpetrator  “CSI” Effect: Juries are now demanding more physical evidence  No longer relying solely on witness statements  Unrealistic expectation that every crime will have physical evidence