1. If an employee identifies multiple witnesses that were “in the room,” or observed an event, how many should be interviewed?

I would suggest that the answer to the question would depend on the relationship of the witnesses to the employee. If two are the employee’s close friend and one is not, I would begin with the person most likely to be neutral. I also think that if you can identify people who were “in the room” that were NOT named by the employee, that those witnesses would offer a “cleaner” version. With that said, I would say to the employee, “If I can only interview two or three of these witnesses, who would be most important for me to speak with and why?” and make sure that at least one person s/he identifies is interviewed.

2. Are there times that an employer should disregard a witness because their credibility is questionable, i.e. a friend of a complainant might have a motive to lie?

One of the most powerful witnesses can be one who speaks against their own interest.  I remember several years ago thinking that it would be a waste of time to interview a witness because of her close association with the respondent. She said to me, “She is my best friend, and I hate to say this, but she did it.” Here, a witness that had every reason to defend her friend did the opposite. If I had skipped that interview, things would still be inconclusive. I would not disregard a witness simply based on a relationship, however, I would use my knowledge about that relationship to “push back,” perhaps asking, “do you believe your friendship with … is affecting your perspective on this issue?”