I dont think police have ever said it was blood, or not.

Most of the case info discussed is similarly unconfirmed.

Cops is either dumb or genius depending on who comments.
Supposedly they want a calm public, but they let wild speculation go on worldwide about what that substance on an OUTSIDE wall is. Horror movie stuff.

If the case can be comprised by the public knowing if that is blood, just say its not. And if its not, just say its not. Maybe they like the public chasing nonsense?

It provides a gory invite for looky-loos to the case.

I think they are leery of saying anything at all, so just clam up.
So wild speculation continues.