Well at least it was someone just taking a dump instead of having real malice. Unfortunate that your toilet didn't work.
Supposedly a common thing criminals with real malice do, from way back in prehistory to now, is poop on the center where the family gathers. In the old days it used to be the hearth; these days it's generally the dining room table. You got the toilet. Could be worse.
Though clean-up of a non-working toilet sounds pretty difficult ...