I have been through this type of thing a few times, once to appear before a grand jury and and a couple of times was deposed at a lawyers office. All were work related. The grand jury was an EPA criminal case, one of my employees had moonlighted during a slow period - and they were after the guy he moonlighted for. The deposing - I was the expert witness.
Without a doubt, the deposing was horrible!! The other lawyer grinding on and on and on. Asking the same question twenty different ways. I didn't have a personal lawyer there, and no judge to step in and say that's enough.
Your situation would be more like mine with the grand jury, pretty painless. Tell them what you did see, keep your answers short - yes sir, no sir, I don't know sir.
IF it actually gets that far -You will be fine!!