What do I do if someone lies to me during a workplace investigation?

What do you do when someone is lying to you or you think someone is lying to you? First and foremost, you are there to be a neutral person whose primary role is to collect facts. And so I think you tell the person that you have concerns about the integrity of the things they're telling you. You probably don't use words like veracity, but you need to poke around the issue. And if they're not catching on that, you have some concerns or are just hunkering down on what you know to be a lie, tell them, is this completely honest? Is this the information you want me to take back to your employer? And if they still lie, then that's their testimony. It's not your obligation to be a truth finder. You must be a fact-finder. And if the corroboration of the evidence indicates that someone's lied to you, then that's what the sum of the evidence suggests.