A woman boss at the BPA (federal Bonneville Power Administration) in Portlandia kept coming into her office, only to find piss and sometimes a loaf as well. The act was very intermittent. This was just before the era of small video cams and DNA. Well, by long term process of deduction, the investigators finally figured they had their guy. But somehow, he got tipped off or got wise to what was coming. Next thing ya know, he's checked into a mental health treatment program for severe work related stress. And instantly became untouchable, and as long as he completed the program, all sins forgiven. Because this was now a health issue, everyone including the boss were forbidden to bring it up, discipline or retaliate. So basically he got away with pissing and crapping in her office for over a year. Once he completed the course, he returned and immediately announced he was retiring.
In my own company, someone left a loathe loaf on a ball breaker boss's desk. It was a one time shot. They never figured out the culprit, and there were apparently too many suspects.