Trial preparation in civil litigation invariably involves the parties deposing one another. But also evidence from a third party—some non-litigant who knows facts pertinent to the case—is important. The rules for deposing a third party, and how testimony from that party may be used at trial, differ significantly from a party’s deposition testimony. Often, however, lawyers do not pay adequate attention to those rules. The consequences can be that valuable third-party deposition testimony will not be admitted at trial, or that harmful testimony may be available to your trial adversary.

Deposing a third party—typically a “percipient witness” who testifies based on what she personally observed, heard, experienced, or participated in—is governed by both rules of civil procedure and rules of evidence.

To have trial ammunition, or to avoid “incoming” from the other side, the lawyer dealing with pretrial testimony of a third party must know these rules and must plan strategically based on them. Whether to depose a third party, how otherwise to preserve a third party’s knowledge, and how to question a third party at a deposition are decisions that should be driven by trial considerations. When confronting a third-party deposition, your mantra should be—“think trial.”