Of American-English origin, the phrase to know where the bodies are buried means to have personal knowledge of the secrets or confidential affairs of an organisation or individual.

A similar image is found in the phrase a skeleton in the closet, or in the cupboard, denoting a secret source of shame or pain to a family or person.

The Oxford English Dictionary (3^rd edition, 2010) erroneously states that to know where the bodies are buried first appeared in the 1940 script of the film Citizen Kane, written by the American film-director and actor Orson Welles (1915-85) and the American screenwriter Herman Jacob Mankiewicz (1897-1953).

In fact, this phrase appeared earlier as to know where the body is buried; the earliest instance that I have found is from one of the unconnected paragraphs making up the column Something to Think About, by Bruno Lessing, in The Monroe News-Star (Monroe, Louisiana) of Friday 6^th April 1928:

It would not be fair to quote more from this book. But something ought to be done to suppress this chap. He knows too much about us. He knows where the body is buried.
                                   (Copyright 1928 King Features Syndicate, Inc.)

The second-earliest instance that I have found is from the column Will Rogers Says, by William Penn Adair ‘Will’ Rogers (1879-1935), American actor, humorist, newspaper columnist and social commentator, published in the Olean Evening Times (Olean, New York) of Saturday 12^th July 1930:

Beverley Hills, Cal., July 12 (Special to Olean Times)—The Republicans are trying to get rid of the chairman of their national committee. They can’t throw him out—he knows where the body is buried.
The next time they hire one his contract will have a two weeks’ cancellation clause in it. They think this fellow don’t add the proper class to the party.
The Republicans want a man that will lend dignity to the office, and the Democrats want a man that will lend some money.
Yours,
Will Rogers.

The earliest instance of to know where the bodies are buried that I have found is from the Daily News (New York, N.Y.) of Sunday 25^th January 1931, which published Hollywood Blackmail Spectre Looms, an article by the American reporter and author Florabel Muir (1889-1970) about “the blackmail racket” in the film industry:

Eddie Doherty, whose accurate reporting more than once gave Hollywood chills and fever in other days, told me when I first came out here:
“These people don’t know you yet. Give ’em time and they will. They’ll find out that you shoot square. Then they’ll start telling you things, things you can’t believe about other people. The funny part is that they will all be true, the things they tell you, hoping you’ll publish them. All of Hollywood is a great spy system with every one trying to get something on the other fellow.”
He was right. You see some obvious incompetent hoisted into a job away over his head and immediately the whisper goes round, “he knows where the bodies are buried.”