I think the intern put poop in the fridge

I'm a first year at a smaller regional bank and my team always takes one or two off-cycle interns. Our off-cycle intern this year is great, funny, and picks up fast. 

Unfortunately, I came in with a few other analysts this morning and found an unpleasant surprise in the fridge. Someone put a rather large piece of poop on a paper plate and wrapped it up like a plate of cookies. I was among the last to leave the night before, and the only person working that morning before me was the intern.  

The intern said they didn't know about anything unusual, but they couldn't stop laughing when I told them what we found. Word got around quickly, key card logins were checked, and it was either one of two VPs from the night before, or the intern that morning. 

I don't even know what to do - I don't think we have any solid proof, and they have publically and privately denied all wrongdoing. We'll see what happens. I'll release her name here if she confesses to it.