The buck stops where in public corruption?

There are chains of command in bureaucracies.

Within chains of command, the laws of physics seem to conflict;
shit rolls downhill, while responsibility flows uphill.
Gravity seems to favor the first. The second, while eminently
justifiable from a philosophical standpoint, disappears entirely
in the face of entrenched corruption; the little guys heads roll,
the heads of the folks who were supposed to be keeping them
out of trouble rarely do.

Take for example the current public corruption and incompetence scandal involving John Dantis, link. Heads will roll, some already have. But what about the person, who did not participate directly in the corruption, but who failed to prevent it?

Is part of the job of any politician or public servant to police the people over which they have direct supervision, or does
"I knew nothing" get them off the hook?

Isn't "I knew nothing", nonfeasance?