Expert witnesses (Forensic Science)
Every person is presumed to be a competent witness. So long as a witness has the ability to observe, recollect, communicate, and speak truthfully, the witness is declared competent. It is the role of the judge to determine a witness’s competency to testify, but it is the role of jurors to determine what weight, if any, they will give to a witness’s testimony. Diminished capacity goes to the weight rather than the admissibility of the testimony. The credibility of a witness’s testimony can be impeached by evidence of dishonesty, conviction of a crime, prior inconsistent statements, or actions demonstrating bias or prejudice. The jury may determine that the testimony of a witness, while admissible, is not probative; alternatively, the testimony may be weakened in the eyes of the jury by one of the factors noted above.
Expert witnesses often work in scientific, technical, or other specialized fields; they are witnesses who have knowledge in particular subjects beyond that of the average person, sufficient that others may rely on their specialized opinions about evidence or matters at issue. Factors that judges consider in determining a witness’s expert status include training and education, experience, familiarity with standard references and authorities in the field, membership in professional associations and societies, and publications. Judges also consider the relevance of the proffered testimony and whether it will actually aid...
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Areas of Expertise (Forensic Science)
Typically, both sides in civil disputes rely on experts for their opinions on matters such as the severity of an injury, its presumed effect on a person’s life, and whether the injury is permanent; the cause of failure of a product or machine; and loss of future earning power. Experts can testify in any case in which their expertise is relevant. In criminal cases, forensic scientists or forensic psychologists are likely to provide expert testimony. Forensic experts who are employed at state crime labs or other public organizations with very high volume of cases requiring them to testify in court frequently prepare reports far in advance of their court appearances.
In 2000, the Federal Judicial Center published the results of a 1998 survey of federal judges and lead attorneys for both plaintiffs and defendants regarding the use of expert witnesses. This study found that medical and mental health cases used more than 40 percent of the experts presented overall. Physicians in all specialties accounted for approximately one-third of all expert witnesses, engineers and other safety personnel accounted for 24 percent, and law, business, and finance experts made up 22 percent of all experts, with economists being the largest type within this group. Scientific experts accounted for about 7 percent of all expert witnesses. When asked about the specific legal issues to which expert testimony had been directed, judges reported that...
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Expert Opinion and Lay Opinion (Forensic Science)
Where jurors are competent to draw their own conclusions on an issue, the use of expert testimony is not proper. Examples are issues of innocence or guilt, fault, and negligence. Sometimes, lay witnesses as well as experts may testify on the same issue from various perspectives, such as the value of property (the owner may give an opinion), the cause of an accident or occurrence, and identity or likeness of handwriting (when a layperson is familiar with the evidence at issue).
Lay witnesses are permitted to offer their opinions about matters with which everyone is familiar: dimensions, including size (large, small), shape (round, flat), and length (short, long); color; weight; sound; time; sense recognition (heavy, bitter in taste); a person’s appearance as it relates to condition (the witness appeared disheveled, elderly, strong, sloppy, wet, agitated, drunk, sober, sleepy, dizzy, irrational, in pain); apparent age; and matters of opinion based on perception or observation, such as the approximate speed of a vehicle (even a “glimpse” goes to the weight rather than the admissibility of the testimony). As long as the witness is not testifying as an expert, the witness’s testimony in the form of opinions or inferences is limited to those opinions or inferences rationally based on the witness’s perception that are helpful to an understanding of the witness’s testimony or the determination of a fact in...
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Relevant Case Law (Forensic Science)
Three court decisions in the 1990’s set out and clarified guidelines for federal judges to use in determining whether and when a particular witness should be allowed to testify as an expert. Daubert v. Merrell Dow Pharmaceuticals, a 1993 U.S. Supreme Court case, established the “gatekeeper” function for judges, in which the judge acts as a filter and is empowered and charged with determining whether a particular expert is allowed to testify in a certain case. The judge can exclude unqualified experts as well as those who deliver unreliable and irrelevant opinions. Factors having a bearing in this area include whether the theory or technique has been tested, whether it has been subjected to peer review, the known or potential error rate, and whether the theory or technique has been generally accepted by the scientific community.
Until 1993, under the “Frye test” or “Frye standard,” which was based on the court’s decision in Frye v. United States, a 1923 D.C. Circuit case, expert testimony had to be based on scientific tests or principles “generally accepted” in the particular field in which the test or principles belonged. The attorneys introduced their chosen experts, and the jury decided what weight to give to the experts’ opinions. Under Frye, therefore, the scientific community rather than the judge determined admissibility of expert testimony. With...
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Battles of the Experts (Forensic Science)
When two or more expert witnesses testify on opposite sides in a case, the jury understandably must decide which opinions to believe. The degree of confidence that jurors place in expert witnesses is related to the witnesses’ experience, training, and credentials and whether the witnesses have performed all the tests necessary. Jurors sometimes feel that they are not qualified to make decisions in complex cases and are grateful to experts who explain technical issues simply and in ways that help the jurors with their task. When both sides bring in highly qualified experts who contradict each other, however, jurors tend to base their ultimate decisions on factors such as the perceived credibility, honesty, and forthrightness of the witnesses and how convincing their explanations are—factors collateral to the testimony.
Juries generally find experts intimidating because the experts have sophisticated and technical knowledge beyond that of the jury. Jurors understandably expect the testimony of expert witnesses to be complicated, confusing, and boring. At the same time, jurors wonder whether expert witnesses are biased because they are “hired guns” paid by the parties for whom they are testifying. In many cases, jurors think that expert witnesses are “too young” to have so much expertise and experience. Such doubts are usually resolved, however, when expert witnesses present their testimony to the jury in a...
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Challenging the Experts (Forensic Science)
Opposing attorneys often attempt to impeach the credibility of an expert witness on the other side by pointing out to the jury that the expert is being paid a fee to testify and a fee to prepare a report and that the expert testifies on a regular basis for the particular law firm. The attorney who called the expert witness to testify can often resolve this situation by affording the expert an opportunity to explain. If an expert has testified on behalf of both plaintiffs and defendants in the past, the expert is not necessarily “neutral.” On cross-examination, opposing counsel may be able to establish that the expert finds favorably for whichever side pays the expert’s fees. This type of inquiry can seriously undermine an expert’s credibility in the eyes of jurors.
Potentially the most effective technique that attorneys use to discredit expert testimony is that of attacking the bases of the experts’ opinions; this is a fundamental element in the cross-examination of opposing experts. If an attorney can convince the jury that an expert was either insufficiently informed or misled because of a failure to consider certain key facts or that key facts were withheld, this can produce a significant impact on the jury. Expert witnesses may also be impeached with prior testimony, prior inconsistent statements, or statements from other witnesses in the case. Inconsistencies place the credibility of expert testimony in...
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Further Reading (Forensic Science)
Broun, Kenneth S., ed. McCormick on Evidence. 6th ed. St. Paul, Minn.: Thomson/West, 2006. Considered the ultimate standard reference on evidence law. Contains detailed explanations and numerous references to case law.
Mauet, Thomas A. Trial Techniques. 7th ed. New York: Aspen, 2007. Handbook covering all aspects of the trial process includes extensive examples of patterns of questions that attorneys use in examining expert witnesses.
Rothstein, Paul F., Myrna S. Raeder, and David Crump. Evidence in a Nutshell. 5th ed. St. Paul, Minn.: West, 2007. Provides a succinct summary of the law of evidence. Useful for both students and practitioners.
Smith, Fred Chris, and Rebecca Gurley Bace. A Guide to Forensic Testimony: The Art and Practice of Presenting Testimony as an Expert Technical Witness. Boston: Addison-Wesley, 2003. Focuses in particular on the use of information technology by expert witnesses.
Stopp, Margaret T. Evidence Law in the Trial Process. Albany, N.Y.: West/Delmar, 1999. Undergraduate textbook intended primarily for paralegals discusses the principles of the law of evidence. A chapter on lay and expert witnesses includes cases and examples.
Wecht, Cyril H., ed. Crime Scene Investigation: Crack the Case with Real-Life Experts. Pleasantville, N.Y.: Reader’s Digest Association, 2004. Accessible work provides a detailed look at...
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Expert Witnesses (World of Forensic Science)
Many criminal and civil investigations turn to expert witnesses in court to help resolve cases where the facts are unclear or in need of some explanation. An expert witness is a person who can provide information and opinion drawn from the body of knowledge that makes up their own area of expertise. An expert witness does not need to be legally qualified. Commonly the witness will be a forensic scientist or forensic pathologist providing information outside the realm of common knowledge about the circumstances of a crime. For instance, a scientist with knowledge of paint analysis or soil can help interpret trace evidence. A pathologist can help with the difficult questions such as the cause of death when a body is recovered from water or what bloodstain evidence might really mean in terms of how someone was killed.
Being an expert witness is not a profession in its own right. The expert witness is created and recognized as such by the judge and the court. There are many databases of people willing to act as expert witnesses in various specialties, and they also have their own professional organizations to represent their interests. The expert witness will have been vetted for suitability; they will also have undergone training in court procedures so that evidence may be given to the best of their ability to help the judge and jury come to a decision. Although many expert witnesses come from a forensic science or medical discipline, they can be drawn from any area of expertise, depending on the circumstances and background of the case. Document examiners and structural engineers may be called in to advise and give evidence, as may those from non-scientific disciplines as diverse as art history, mountaineering, or martial arts.
Either prosecution or the defense may call in an expert witness. He or she is expected to look at the evidence relevant to their discipline and put it in the context of the whole case. They will produce a report that can be taken up into the witness stand. First of all, the party who engaged the expert witness will ask questions that prove identity, experience, and background to the court. Then they will ask questions that generally take the court through the expert witness' report.
The expert witness can expect to be cross-examined by the opposing counsel. That is, an expert witness for the prosecution will be questioned by lawyers for the defense, and vice-versa. The other side may also engage their own expert witness. The purpose of cross-examination is to find flaws in the evidence and conclusions presented by the expert witness. Many people are experts in their own subjects, but it takes special skill and training to defend one's findings in public while still remaining objective and impartial.
The expert witness has a large responsibility, as the manner of giving evidence can influence the judge and juryhe decision makers in the case. Expert testimony is especially important when other evidence is insufficient to help come to a clear verdict. At the same time, in a stalemate situation, the expert
The expert witness is the only one in court who is allowed to give opinion as well as facts. This is because the court has confidence in the facts and knowledge on which the opinion is based. Thus, the forensic psychiatrist is allowed to say, "I believe this man to be capable of this murder, with this degree of violence, based upon my assessment of his mental state." With other evidence, that opinion may be what is required for judge and jury to make up their minds in the case.
SEE ALSO Evidence.