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Law 101: Legal Guide for the Forensic Expert


Cross-examination: The expert witness may be called upon to retrace his steps, explain and justify his position, and harmonize his views in the case with prior writings, depositions or trial testimony from other matters/cases.

Cross-examination is one of the most misunderstood aspects within the adversarial system. It need not be a fearful experience for the expert. Cross-examination is designed to guarantee a fair trial. With regard to experts, cross-examination has six general purposes. These are to establish the expert's:

  • Lack of perceptive capacity or application (i.e., failure to do one's homework).
  • Inadequate recollection of the applicable facts.
  • Bias, prejudice or interest in the outcome (or motivation to give a particular testimony).
  • Questionable character, reputation or qualifications.
  • Prior inconsistent statements or conduct (i.e., if the expert testified to different conclusions in another case in which the facts and evidence were approximately the same, that can be used to impeach their testimony).
  • Inconsistency with recognized published authorities, so-called learned treatises.

Cross-examination can present an opportunity to solidify and drive home the expert's conclusions and opinions previously stated during direct examination. Witnesses should be honest and should rely on their technical expertise and the scientific method, on which their testimony is based. They should provide credible and effective expert testimony and should be able to use cross-examination in a positive way. (See Trial for further information.)

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