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