The phrase piano player in a brothel, and its variants, are used of a person who is implicated in an activity but accepts no responsibility for it.

This phrase occurs, for example, in Dingell has America’s problems in focus, by Bob Talbert, published in the Detroit Free Press (Detroit, Michigan, USA) of Tuesday 17^th February 1987:

“Do you believe Ronald Reagan?” said powerful U.S. Rep. John Dingell Jr. (D-Mich.). The sarcasm was curling around the name as we discussed the Iranian-Contra arms scam and cover-up. “Reagan sits there like a piano player in a bordello when asked if he knows what’s going on upstairs: ‘Me? I don’t have the vaguest idea. I’m just the piano player here.’”

The phrase piano player in a brothel and variants were used in particular during the Watergate scandal by William Bart Saxbe (1916-2010), Senator from Ohio, to characterise Richard Milhous Nixon (1913-1994), President of the United States.

The earliest occurrences of the phrase piano player in a brothel and variants that I have found are as follows, in chronological order:

1-: From CRY, my beloved country, about South Africa, by the South African-born British journalist and lyricist Herbert Kretzmer (1925-2020), published in the Sunday Dispatch (London, England) of Sunday 3^rd April 1960:

It has been said of the English in South Africa that while the fear the Boer they fear the black man more—so that they are reduced to the status of piano-players in a brothel who prefer to shut their eyes to what is going on.

2-: From the transcript of the parliamentary debates that took place at the Australian House of Representatives in Canberra, Australian Capital Territory, on Thursday 21^st September 1972—source: Parliament of Australia:

SYDNEY TRADES HALL VIOLENCE

Mr BURY—My question is addressed to the Minister for Labour and National Service. Have there yet been any successful prosecutions following the violence in the Sydney Trades Hall 3 or 4 weeks ago and, apart from those, have any prosecutions been begun or conducted, or has effort been made to hush the whole thing up in the hope that the public will forget it? To what extent do these crude and brutal louts and larrikins cow and dominate the union movement? Is it appropriate at this stage for the Australian people to make these law breakers our law makers and rulers? In the last 2 years, has the relative number of offices held by, and the strength of, the Communist Party within the trade union movement greatly increased and, with that, has the application of bullying and physical violence increased? Have the trade union leaders paid any more than lip service to decrying violence? Have they taken any effective action or have they adopted the general, traditional attitude of the man playing the piano on the ground floor of the brothel and affecting neither to know nor care what goes on upstairs?

3-: From Impeachment Is a Dangerous Thing, an editorial published in The Portsmouth Herald (Portsmouth, New Hampshire, USA) of Thursday 7^th June 1973:

We would agree with the President’s critics that his complicity at least in the coverup of the Watergate scandal is becoming increasingly obvious. The President of late has been too much like the proverbial piano player in a brothel, always pretending that he didn’t know what was going on upstairs.

4-: From the following story, published in several Canadian newspapers on Wednesday 31^st October 1973—for example in The Ottawa Citizen (Ottawa, Ontario, Canada):

WASHINGTON (Reuter)—Senator William Saxbe (Rep. Ohio), who once suggested President Nixon had taken leave of his senses, said Tuesday White House officials had preliminary discussions with him on the possibility of his becoming attorney general of the United States.
[…]
The 57-year-old senator said during last December’s heavy American bombing of Cambodia that he thought the president had taken leave of his senses.
He also once said that for the president not to have known what was going on in the Watergate political espionage affair was like a piano player in a brothel not knowing what was going on in the bedrooms upstairs.

5-: From KNOWN FOR PUNGENT PHRASES Saxbe has his own law of speech, published in The Star-Ledger (Newark, New Jersey, USA) of Sunday 11^th November 1973:

WASHINGTON—[…] We’ve been treated during the past few days to reruns of some of Saxbe’s salty rhetoric. Among them were his publicly questioning the President’s mental state during the Cambodian bombing, his likening of Nixon’s Watergate defense to that of the piano player in a bordello who claims not to know what goes on upstairs, and his suggestion in Hong Kong and elsewhere that incriminating tapes would never see the light of day.

6-: From an article about William Saxbe, by Nick Thimmesch (1927-1985), published in several U.S. newspapers in January and February 1974—for example in The Sun (Baltimore, Maryland, USA) of Tuesday 29^th January:

As senator, he once said he thought the President lost his senses; was like a man playing piano in a bawdy house who said he didn’t know what was going on upstairs, and that the ineptness of Mr. Nixon’s lieutenants entitled them to wear clown suits.

7-: From Morality of Human Research Debated, by Toni Martin, published in The Hartford Courant (Hartford, Connecticut, USA) of Friday 10^th January 1975:

Thomas Halper of the department of political science at City University of New York said that any researcher who participates in a study with a purpose he abhors is like “the piano player in a brothel who insists he’s only there for the music.”

8-: From Data Panel Stands Firm In Recommending Itel For Computer Contract, by Maureen Brown, published in The Columbus Dispatch (Columbus, Ohio, USA) of Tuesday 14^th November 1978:

The Franklin County Data Processing Board reaffirmed its recommendation Monday to award the bulk of a computer hardware contract to Itel Corp. of Cincinnati, while one member lambasted IBM for its maneuvering to get the contract.
[…]
County Treasurer Dana G. Rinehart, a member of the data board, told IBM representatives at a board meeting Tuesday he was stunned by their 11^th-hour attempts to circumvent the board and the task force.
“I am absolutely stunned at your conduct, Mr. McCullough, with respect to this contract,” Rhinehart said to Paul McCullough, an IBM salesman.
HE SAID IBM could have contacted the task force anytime during its 14-month study of the computer contracts, but instead chose to wait until the last minute.
McCullough responded that his company did not have all the information it needed until last week. Rinehart rejected that contention, saying it was similar to a piano player in a brothel claiming to be unaware of the establishment’s true business.