Federal Court (Forensic Evidence)

The Federal court system creates the standards, rules, and procedures for use by all of the lower courts in the nation. Four Federal Rules of Evidence are of particular significance in the world of forensic science.

Rule 702 involves testimony by experts. The pertinent text of the Rule states "If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training, or education, may testify thereto in the form of an opinion or otherwise, if (1) the testimony is sufficiently based upon reliable facts or data. (2) the testimony is the product of reliable principles and methods, and (3) the witness has applied the principles and methods reliably to the facts of the case."

In 1993, a Supreme Court case entitled Daubert v. Merrell Dow Pharmaceuticals resulted in a ruling that when expert evidence based upon scientific knowledge is part of the evidentiary proceedings in a trial, and the testimony is questioned or challenged by the litigant, the judge is responsible for acting as a "gatekeeper" who must decide whether the expert testimony should be considered scientifically reliable or valid. The gatekeeping function extends to technical and other potential specialized knowledge as well as to scientific knowledge.

As a result of the Daubert decision, many of the lower courts had to examine whether the Daubert factors applied to decisions about the reliability of expert evidence need also be applied to expert witnesses who were not offering opinions based strictly on scientific principles, but on specialized or technical knowledge. The general consensus was that the Daubert rules should be applied to all expert opinion testimony.

The Daubert rules were extended and clarified in 1999 by another Supreme Court decision, Kumho Tire v. Carmichael, in which it was mandated that trial judges act as gatekeepers who must make certain that only reliable expert opinion evidence and testimony be admitted, and that this rule apply to all possible forms of expert testimony. The text of the Committee Note following that decision is as follows: "The specific factors explicated by the Daubert Court are: (1) whether the expert's technique or theory can be or has been tested—that is, whether the expert's theory can be challenged in some objective sense, or whether it is instead simply a subjective, conclusory approach that cannot reasonably be assessed for reliability; (2) whether the technique or theory has been subject to peer review and publication; (3) the known or potential rate of error of the technique or theory when applied; (4) the existence and maintenance of standards and controls; and (5) whether the technique or theory has been generally accepted in the scientific community."

As a result of the Kumho Tire decision, the Court publicly stressed that these factors might not necessarily be fully applicable to all forms of expert opinion testimony, that the factors were more on the order of guidelines than rigid requirements, and that there might be specific situations or circumstances in which lower courts might give equal consideration to other factors that might best permit assessment of reliability or validity of nonscientific expert opinion testimony offered during a trial.

Among the procedural conclusions of Daubert was an assertion that the judicial decision regarding reliability for admissibility of evidence lay in the principles and methodology of techniques rather than on the conclusions reached by applying them. In the 1997 case General Electric v. Joiner, the Court partially reversed that language, by stating that it is not always possible to separate conclusions from the methods by which they were reached.

In its current wording, Rule 702 directs trial courts to determine not only whether an expert's analytic methods are based upon sound and scientifically accepted principles, but whether the expert used those methods in a reliable and scientifically appropriate manner, in order to reach the conclusions stated in testimony regarding the disputed facts of the case.

The relevant portion of Rule 703, regarding bases of expert opinion testimony, states: "The facts or data in the particular case upon which an expert bases an opinion or inference may be those perceived by or made known to the expert at or before the hearing. If of a type reasonably relied upon by experts in the particular field in forming opinions or inferences upon the subject, the facts or data need not be admissible in evidence in order for the opinion or inference to be admitted. Facts or data that are otherwise inadmissible shall not be disclosed to the jury by the proponent of the opinion or inference unless the court determines that their probative value in assisting the jury to evaluate the expert's opinion substantially outweighs their prejudicial impact."

In the original version of the Federal Rules of Evidence (1975), experts could base their opinions not only on facts brought into evidence, but also on facts not in evidence, and even on facts which would not under any circumstances be admissible as evidence, as long as the non-admitted or non-admissible facts were part of the aggregate body of knowledge that other experts in the same field of study would utilize in making professional judgments in situations not involving litigation. To clarify, the Federal Rules of Evidence sought to allow a subject area expert the latitude to use relevant and appropriate professional tools in order to render the most accurate and informed opinion possible, and to be able to communicate that decision to the participants of a particular proceeding in a court of law.

Rule 701 concerns opinion testimony given by lay witnesses. The significant portion states, "If the witness is not testifying as an expert, the witness' testimony in the form of opinions or inferences is limited to those opinions or inferences which are (a) rationally based on the perception of the witness, (b) helpful to a clear understanding of the witness' testimony or the determination of a fact in issue, and (c) not based on scientific, technical, or other specialized knowledge within the scope of Rule 702."

Members of the general public, as non-expert witnesses, may offer their personal opinions as evidence in situations where they have very strong recollection of specific events. They may testify as to what they observed or perceived: "he appeared to be drunk and his clothing smelled of beer," or "she was driving a great deal faster than the 15 mile per hour speed limit in the school zone." This rule does not permit expert witnesses to offer their perceptions, thoughts, or opinions in the guise of lay testimony.

Finally, Federal Rule 706, in relevant part, states, "(a) Appointment. The court may on its own motion or on the motion of any party enter an order to show cause why expert witnesses should not be appointed, and may request the parties to submit nominations. The court may appoint any expert witnesses agreed upon by the parties, and may appoint expert witnesses of its own selection. An expert witness shall not be appointed by the court unless the witness consents to act. A witness so appointed shall be informed of the witness' duties by the court in writing, a copy of which shall be filed with clerk, or at a conference in which the parties shall have the opportunity to participate. A witness so appointed shall advise the parties of the witness' findings, if any; the witness' deposition may be taken by any party; and the witness may be called to testify by the court or any party. The witness shall be subject to cross-examination by each party, including a party calling the witness...(c) Disclosure of Appointment. In the exercise of its discretion, the court may authorize disclosure to the jury of the fact that the court appointed the expert witness."

Federal Rule 706 essentially states that the court has the discretion to appoint or to deny appointment to any expert witness agreed upon by both parties; it also has the right to select its own expert witnesses, as well as the right to inform the jury that it has done so. In theory, a court-appointed expert is truly objective, as he or she is not employed by either party, the court-appointed expert has no potential loyalty to anything other than an unbiased assessment of the facts at hand.

These Federal Rules of Evidence are of particular importance for the forensic scientist: they inform the way in which expert witnesses may be used, the means with which the term "expert" must be defined, the role of the general public as trial witnesses, and the impeachability of expert witness testimony based on who is the employer of the expert.