Are you sure about that? It's hard to bury people in the Keys because of hard limestone just under the surface. I read that the victims of the 1935 hurricane had their bodies piled in pyramids and then set ablaze.
OK, I stand corrected. They were cremated and the ashes put in an above ground crypt.
You are correct.
I doubt the mass grave angle unless they had machinery that digs through cap rock in the 30’s.