Skeleton in the closet

Skeleton in the closet is a colloquial phrase and idiom used to describe an undisclosed fact about someone which, if revealed, would damage perceptions of the person. It evokes the idea of someone having had a human corpse concealed in their home so long that all its flesh had decomposed to the bone.
It is known to have been used as a phrase as early as at least November 1816. In the most derisive of usage, murder, or significant culpability in a years-old disappearance or non-understood event, may be implied by the phrase.