In a workplace investigation, a corroborating witness is a person whose evidence supports or confirms the evidence of another witness, including a complainant or respondent. Given that people’s memories naturally fade over time, minor inconsistencies between witness accounts are often not significant and, in many cases, to be expected. But what about identical or near-identical witness accounts that emit that “too good to be true” feeling?

If this happens, an investigator may be looking at two possibilities. The first is collusion. This occurs when witnesses intentionally conspire to fabricate a version of events or agree to tailor their evidence so that they appear to be reciting a consistent and reliable story. The second is the inadvertent tainting of evidence, which occurs when witnesses unintentionally influence one another’s evidence by discussing the incident that is the subject of the workplace investigation.

It is not unusual that people who have witnessed the same incident will discuss it. Very often this has already happened before an investigator has been assigned and has had a chance to caution witnesses against discussing their evidence with one another. Rumour and gossip can also fuel discussions about incidents in the workplace.

Being alive to the possibility of collusion and inadvertent tainting is part of an investigator’s job when it comes to weighing the evidence before them. Some signs of collusion and/or tainting include:

• • The use of identical (or strikingly similar) words, phrases, or expressions by two or more witnesses: This could mean that witnesses have intentionally coordinated their evidence, or it could suggest something more innocent. Witnesses may have shared information with one another at some point, with the unintentional consequence of altering the way they talk about an incident, and possibly even their memory of the incident itself.

• • Evidence that sounds rehearsed: Evidence that is rehearsed because of collusion can present in a variety of different ways. For example, a witness may have a stilted manner of speech as they struggle to retrieve information that they memorized in concert with another witness, or the specificity with which they recount certain details may stand in stark contrast with the vagueness of the remainder of their evidence.

• • Evidence that shifts during the course of the investigation: If a witness changes their evidence between their first interview and a follow-up interview, and their new evidence happens to align with the evidence of another witness, an investigator may be looking at collusion. This is especially the case where the witness has no reasonable explanation for the change.

Beyond recognizing these and potentially other red flags, an investigator ought to know how to factor collusion and inadvertent tainting into their fact finding. Figuring out which of these two is at play is key to guiding the investigator’s assessment of the evidence. A good place to start is to ask the witnesses in question if they have discussed their evidence with anyone else. Moreover, asking this question is necessary to ensure a fair process. An investigator should not draw conclusions about a witness’ credibility without giving them an opportunity to respond to the investigator’s suspicions.

If witnesses are open and forthright about having discussed their evidence with one another, and there are otherwise no issues with their credibility, this likely eliminates concerns about collusion while leaving open the possibility of evidence tainting. On the other hand, collusion is more likely if witnesses deny having spoken to one another, but the red flags noted above suggest otherwise. In the end, the investigator must consider the totality of the evidence, including the motivations of the witnesses and the plausibility of collusion, in deciding what is likely to have occurred.

To be clear, an investigator is not making a separate finding of fact with respect to collusion or inadvertent tainting, unless this is part of their mandate. Rather it is the likelihood, on a balance of probabilities, that either of these are at play that factors into a witness’ reliability or credibility.

The existence of collusion leads to a relatively straightforward credibility assessment. Collusion is inherently deceptive and detrimental to a witness’ credibility, regardless of whether it is done to completely make up a story or to avoid giving inconsistent evidence about an incident that occurred. The evidence of those who collude will inevitably be diminished because the investigator cannot trust the honesty and sincerity of their accounts. And while the fact that witnesses colluded does not mean that an incident did not occur, it does mean, at the very least, that their evidence is less reliable.

By contrast, the fact that witnesses have innocently discussed their evidence requires a different and more nuanced analysis that focusses on the reliability of their evidence.¹ The fact, alone, that witnesses have discussed an incident that is the subject of an investigation does not necessarily mean that their memory of the event is unreliable. An investigator should ask questions to determine who shared what with whom, and the level of detail that was discussed. The likelihood of evidence tainting will be higher where, as noted above, witnesses use identical words or phrases to describe an incident. However, this should not automatically lead to an investigator discounting, in its entirety, the evidence of the relevant witnesses. The reliability of each witness’ evidence should be weighed independently with reference to all the relevant circumstances, and this analysis should be clearly articulated in the final investigation report.

Unfortunately, collusion and inadvertent tainting come up from time to time in workplace investigations. An investigator who knows what to look for and what to do next is well-equipped to weigh the evidence before them in a thoughtful and thorough manner.

¹ See R. v. C.G., 2021 ONCA 809 (CanLII), at paragraphs 27-40, where the Ontario Court of Appeal discusses the differences between collusion and inadvertent tainting that are addressed in this blog, and how a trial judge is to deal with this evidence. Although the decision is in the criminal context, the Court’s comments are applicable to the credibility assessments that occur in workplace investigations.

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