Assessing Witness Credibility—Is it Really Just “Opinion”?


I was challenged recently by a participant during an in-depth webinar on conducting investigations of employee misconduct that I was leading. As I discussed how to assess witness credibility—one of the most difficult challenges investigators face—the participant sent me a message that said, “Not to contradict you, but the Association of Certified Fraud Examiners (ACFE) states that investigators should not rely on their opinion in reaching a conclusion.” Of course, the participant was contradicting me, but more importantly, they were implying that that assessing witness credibility is really just a matter of subjective opinion. It’s not an uncommon view, but it is one I wholeheartedly reject. Here’s why:

The Investigator’s Role—More than Evidence Gatherer

The key to understanding the validity of witness credibility assessments lies in the investigator’s role. The investigator’s job is not to simply collect evidence. Instead, after collecting as much evidence as is reasonable and feasible, the investigator must analyze the evidence to determine what it suggests actually occurred.

It is the rarest of rare investigations in which all of the evidence points solely in one direction. Instead, there almost always is some inconsistency/conflict between different pieces of evidence. 

When there is conflicting evidence, the investigator must carefully review and determine which evidence is most reliable—and thus persuasive—in helping determine what actually happened. This is true for documents and records just as much as it is for witness statements.

Analyzing Evidence: A Typical Scenario

To help illustrate how witness credibility assessments are not just subjective opinion, let’s first think about conflicting documentary evidence.

Imagine, for instance, that you are investigating an allegation that a particular employee accessed a database of highly confidential information without authorization. You have clear evidence from the IT department showing that the computer assigned to the accused employee, and to which only he was given the logon and password, was used to gain the unauthorized access. The employee, however, denies that he was even at work on the day the unauthorized access occurred.

When you check the records of which employees entered the building on the day in question, the records confirm that the accused employee did not enter the premises, just as he claimed. (Employees are required to use their badge to open every external door to the building, and the accused employee’s badge was not used on the day in question.)

Evaluating Conflicting Evidence

When confronted with conflicting evidence like this, a good investigator examines the evidence to determine if there are potential weaknesses in it. He/she also seeks additional evidence (corroboration) that will help clarify which report—the IT logs or the entry/exit records—is more reliable.

For example, is it possible for employees to follow someone else into the building after that person uses his or her badge to open the door? Did the accused employee give his logon and password to anyone else, or could someone have discovered them?

Ultimately, the investigator analyzes the degree to which each of the original documents is reliable and then weighs that them, along with all other evidence gathered in the investigation, to determine what the evidence collectively indicates most likely occurred. (Remember, without perfect, air-tight evidence, we are always dealing with probabilities regarding what occurred.)

Assessing Witness Credibility  

When one witness contradicts another, the process is the same—the investigator analyzes the degree to which each witness is reliable.  To do this, we recommend that investigators use five “credibility assessment factors” to help structure their analysis:

  •          Plausibility of the witness’s statement
  •          Witness demeanor
  •          Corroboration
  •          Past record
  •          Motive

No single factor proves that a given witness is truthful or lying, but—collectively—the factors help the investigator assess the degree to which a witness’s statement should be relied upon in reaching a conclusion. Thus, in the same way that the investigator examines documentary or electronic evidence for weaknesses/reliability, she/he examines information gathered from witnesses and determines the degree to which that evidence is reliable. 

In other words, the credibility assessment is not subjective opinion but, instead, reasoned analysis based on the evidence.

Finally, for those who doubt the validity of assessing witness credibility, consider this: Witness credibility assessments are a standard, essential part of what judges, juries, and other fact finders do as they assess what actually happened in the case before them.

To gain even greater insight into best-practices for all aspects of ethics and compliance investigations, consider joining me for my upcoming one-day online training seminar, Seven Steps to Investigate Alleged Employee Misconduct & Writing Investigative Reports. More details about the seminar and registration can be found here.


DISCLAIMER: Because of the generality of this update, the information provided herein may not be applicable in all situations and should not be acted upon without specific legal advice based on particular situations.

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