What Do I Do if An Interviewee Does Not Know the Answers?
What do you do if your interviewee does not participate in the investigation, or does not know what you are asking them? That's kind of two different issues. So, if the person does not participate in the investigation, you need to, again, remind them that their employer expects them to participate, and it is likely something that they could be written up or even terminated over because all employees are expected to abide by a reasonable instruction from the employer.
If they don't know what you're talking about, you need to double-check that it's not your question style, that you're not the reason that they don't know what you're talking about. But if they don't know what you're talking about because they were not in the room, they did not hear the thing, they haven't experienced the damage, whatever it is, you have done your job.
Sometimes it happens that an interviewee tells you, "Oh, Betty heard that," but when you talked to Betty she says, "I have no idea what you're talking about." She didn't hear it at all. And you just write in your report, "We were told that Betty heard it, Betty reported she had not heard that thing or anything similar to it and did not have information about whatever the crux of the issue was." That happens sometimes, that people don't hear the things. And sometimes you need to really poke about what is underneath it. So, asking somebody the question, "Have you ever heard any bullying behavior?" We all interpret the word bullying differently, but if somebody says, "No, I haven't." Okay. Well, "Have you ever heard anybody call anybody else stupid?" Sometimes when you get down to the nitty-gritty, you'll get different answers. Yes. I've heard somebody call Tom down the hall stupid. It was our manager, our manager said that. Oh, okay. But you didn't regard that as bullying. And maybe they will say, "Oh, well, now that you say it, I guess maybe I do." Or "No, that's just how they play around." Anyway, the point is that if somebody doesn't know what you're talking about, you need to double-check that it is not your own question style that's leading to that confusion. Because if it really is that they just don't know, then that's the answer to your investigation.