know where the bodies are buried

as you know

as it is already known.

buried treasure

Something valuable that is concealed for a long time and then rediscovered.

dead 'n' buried

Contraction of dead and buried.

dead and buried

Of an issue, moot, passed, irrelevant, forgotten.

fuck if I know

I have no idea whatsoever

hell if I know

Synonym of I don't know.

I don't know about that

I am not sure that I agree; expressing doubt or skepticism.

I hardly know her

A joking retort that draws attention to the possibility of sexual innuendo when a word ends with a schwar.