When preparing for a cross-examination, the skilled litigator must always first determine his “theory” of the cross: Specifically, it must determine if the suggestion to the jury is that the witness is truthful, honest but mistaken, or purposely exaggerating or shading his testimony to help one particular party. Where the theory of the cross-examination is that the witness is intentionally attempting to mislead the jury, then exposing the reason for the witness’ deception, i.e., his bias, is a crucial goal of the cross-examiner. Asking questions which allow the jury to see that the witness is not as credible as he or she would have the jury believe is a key component of this type of attack. But when dealing with the expert witness, exposing bias is not only an essential part of cross, but one that becomes imperative if counsel is to turn the jury against the so-called “expert.”
To expose such bias, one of the most effective methods is to focus on matters collateral to the central issue(s) in the case. This cross-examination technique, known as the collateral attack, can be one of the most effective methods to discredit the expert. At its core, exposing bias through the use of the collateral attack is one of the greatest and most time-tested techniques available to counsel. It goes without saying that the bias, hostility, or motives of an expert witness are relevant and proper subjects for impeachment.
