We have a problem at work. Known employee continues to "dirty" the toilet seat daily while ignoring it. Help!!?

Every day we can count on a fellow employee to apply a dirty smear on the toilet seat condsisting of a combination of sweat, hair, & what appears to be a bit of feces. It appears to be strategically placed in the back center of the seat every time. We have 3 stalls and each is supplied with flushable paper toilet seat covers which he obviously deems unnecessary considering we clean up after his every "move". Our heavy-set "Brown Bandit" favors the roomier handicap stall. After years of this going on, we've placed a spray bottle of Simple Green cleaner in that stall so the next victim is able to clean the smear mark. It's really gross and it's the last thing you want to have to deal with when duty calls. Everyone knows who it is but, considering his size and the risk of denied accusation, no one has said anything. I've considered consulting HR and even putting up a tactful sign in the stall suggesting that you check the seat for skid marks before you leave. For years we've hoped that he would realize his infractions and take responsibility for cleaning up after himself or at least using the readily available seat covers. No such luck. Our primary suspect has been caught in the act through careful detective work. Myself and other employees have seen him emerge from the stall leaving the seat in its gritty glory. No one in their right mind would have sat in what we're sure he left there (even him) so he's the obvious infractor. A co-worker of mine even watched him exit the stall a few months ago and, in an attempt to cover his tracks said, "Man! someone left a mess on that seat!" This was just after he finished using it! Come on man!!! I hate when idiots think everyone else is dumber that they are. To give everyone a brief profile of this dude, he's a big burly fellow who's very large. He has a long ponytail & unkept facial hair. Pardon my disrespectful description of this sbag but he's the epitomy of a neanderthol, mentally AND physically. We are all at our wits end and we just can't take this anymore. Does anyone have any feasible suggestions for putting an end to this? I wouldn't have taken the time to address this problem here unless it was out of control or if we felt we had another course for resolve. Please help. Our HR department is very strict about what we say to our coworkers and nobody wants to say anything for fear of their lives. What do we do?? I can only imagine what this guy's toilet at home looks like. Especially withous us to clean up after him. Can you believe he's married??? Maybe she's become used to it but I know we won't. Thank you for reading and I'm sorry if you just ate.