Internal investigations are more important than ever before, with reports of alleged wrongdoing in the workplace becoming increasingly public. Whether prompted by alleged fraud, regulatory non-compliance, company policy violations, sexual harassment, or other misconduct, internal investigations all depend upon a fundamental element: witness interviews.

In all investigations—even the most paper-heavy—witnesses are required to narrate the story. Witness statements provide critical context to existing documents and data and are often the sole source of information on central topics. Investigators routinely rely on witness statements as the basis for their investigative findings and client recommendations, meaning an investigator's subjective belief that a statement is true or false may lead to termination, loss of licensure, loss of revenue, civil or criminal fines, or even prison time. Given the important role witness interviews play within the investigative process, investigators must carefully parse witness statements to determine whether and to what extent they are credible.

But can you tell if someone is telling the truth?

The simple answer is often no. There is no such thing as a human lie detector. Be skeptical of someone who purports to be able to tell whether a person is lying based on facial expressions or body language. These signals can be useful with someone you know very well, but are much less so when the subject is unfamiliar. Over-reliance on "gut instinct" and demeanor evidence can impede a true credibility assessment and result in biased decision making. To avoid these outcomes, investigators must assess both the statement and the witness using the following factors:

  • Is the witness's story inherently plausible? A statement is more credible if it makes sense and can be believed on its face. To be believed, a witness's statement should be reasonable in light of the other evidence. Any inconsistencies—both external and internal—should be carefully examined with the witness before making a determination on credibility.
  • Are the witness's statements corroborated by other evidence? Corroborating evidence is strong indicia of credibility and can include statements from others with knowledge of the underlying incidents or who previously spoke with the witness about them, as well as physical evidence, like documents, e-mails, text messages, and surveillance footage that support the witness's statements.

To identify potential corroborating evidence, ask, "If this is true, what else must be true?" For example, an account manager's statements that he overbilled employee hours on an invoice due to inadvertent error, rather than fraud, could be corroborated by documents showing the overbilled amounts were passed through in wages to the manager's hourly employees, rather than pocketed as company profit.

  • Does the witness have a motive to lie? A witness is motivated to lie if he or she has a personal stake in the outcome of the investigation. This factor should be interpreted broadly and could include anything from fear of disciplinary action or lost profits to a relationship with a more involved party. Any witness who could gain or lose from the outcome of the investigation has a motive to lie.
  • Did the witness have the ability and opportunity to know, remember, and relay the facts? Was the witness in a position to clearly observe what they are reporting? Are there any impediments to the witness's perception, such as distance, lighting, obstruction, intoxication, or lack of sleep? Does the witness's age or experience affect his or her ability to understand what is being observed and accurately describe it? A lack of ability or opportunity to know and accurately relay the facts weighs against credibility.
  • How (and how well) does the witness know the facts? Investigators should consider how the witness came to learn the facts at issue—e.g., through firsthand knowledge, review of documents, discussions with others—as well as the clarity with which the witness can recall them. Witnesses should be questioned about their preparation for the interview and discussions of the subject matter with others to identify potential issues with their ability to recall the incident(s) in a credible manner, including confirmation bias. For example, witnesses who repeatedly discussed a colleague's odd behavior may conflate and misremember what they personally observed.
  • What was the witness's manner? Did the witness seem frank and direct or were they evasive? Did they appear to be telling the truth? Investigators should avoid placing too much weight on witness demeanor, which can vary across and between cultures, to reduce potential unconscious bias and bad findings. But inconsistent statements, a tendency to exaggerate, or prior instances of misconduct can significantly impact an investigator's credibility assessment.

Factors focused on the statement itself evaluate what facts are being reported, while factors examining the witness focus on who is reporting those facts. Each is important to assessing credibility and should be carefully considered before making investigative findings or recommendations. As courts commonly instruct juries, however, you should rely in the last analysis on your own experience, good judgment, and common sense.

The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.