Who Shot John Meaning

(idiomatic) Something bad; a mess.

Example: 1917 April, Hal B. Stroup, “letter”, The Bricklayer, mason and plasterer, volume 20‎, Bricklayers, Masons, and Plasterers International Union of America, page 25:
  This "Who-Shot-John" stuff about "Love thine enemy" is all very pretty, but I would rather have a little regard and do a good turn for a man that has proved himself my friend by having stuck to the organization that has raised my wages and thereby making It possible for me to give my family more of the necessities of life.
1979, Mr. Morris, quoted in Reauthorization of programs under the Justice System Improvement Act of 1979 : hearing before the Subcommittee on Crime of the Committee on the Judiciary, House of Representatives, United States General Printing Office, page 17,
  I really do not think it is appropriate to come up here and present to this committee or to the Congress the "who shot John" processes by which the President makes decisions.
1987 May 13, Ms. Gradison, quoted in The Clayton Act Amendments of 1987 (railroad antitrust immunity) : hearing before the Subcommittee on Antitrust, Monopolies, and Business Rights of the Committee on the Judiciary, United States Senate, United States General Printing Office, page 88,
  Yes, sir. And I thought that might come up, so I brought the who-shot-John on it.
2004, Thomas Friedman, quoted in International Media Seminar on Peace in the Middle East Staff, Role of Civil Society in Promoting a Just And Lasting Peace in the Middle East: An Israeli-Palestinian Dialogue, United Nations Publications, ISBN 9211009766, page 67,
  That was the intervening event. I raise that not to start this whole who-shot-John-first, but to say that if we are going to talk about these events, we have to talk about them in the full and complete context.
1985, JT O'Reilly, LABOR LAW COLLOQUIUM: The First Anniversary of the Ohio Public Sector Collective Bargaining Law:
  ... Adjudication procedures are great for "who shot John" questions, but not for the great mass of policy issues which will come before the Board in its first few years.
2009, J Bravin, “Justice Stevens Renders an Opinion on Who Wrote Shakespeare's Plays”, Wall Street Journal:
  To her, however, the authorship evidence is inconclusive. Besides, "coming off a college education in postmodern literary theory, I was mildly troubled by the 'who-shot-John?' interest in who the real Shakespeare was," she says. "My view is that the work stands on own."
2008, Theresa Renee White, Media as Pedagogy and Socializing Agent
  "I don't know why you wanna run around looking like Who Shot John," exclaims Monica's mother, played by Alfre Woodard. These words may seem a bit harsh, but they were supposedly said with a loving sentiment.
2012, Cattina C. Coleman, To Have, To Hold, and To Never Let Go
  I know this topic goes both ways because there are women who also fall short in this area and need to douche on a regular basis with the way they are running around smelling like “who shot John”. However, the topic is on you men […]