This will take some investigation.
Who in their right mind would accidentally shit on the toilet seat and then walk away and leave it? Who wouldn't even make an attempt to clean up after themselves?
I can think of only one person who might commit such a deed with forethought...
...The Serial Shitter.
Which is kind of odd, because I don't think that the man we've always suspected of BEING the Serial Shitter even came in yesterday.