lone gunman

From the Warren Commission's lone gunman theory, that the assassination of U.S. President John F. Kennedy was the work of a single individual, subsequently applied to numerous other political assassinations and shootings.

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lone gunman (plural lone gunmen)

1. (idiomatic) An individual person who acts on his or her own initiative, without partners, especially one who has sole responsibility for doing something questionable, confidential, or iniquitous.
   • 2002, Jed Mercurio, Bodies, →ISBN, page 340:

     He continues, "So when someone blows the whistle, the hospital has to start looking for a scapegoat. The hospital looks for the lone gunman—the individual, acting alone, acting counter to his training, who, through a gross act of incompetence . . . ."

   • 2008, John Grisham, The Appeal, →ISBN, pages 197–198:

     Trial lawyers, always a colorful and eclectic bunch. . . . Most were lone gunmen too eccentric to keep much of a staff.

   • 2008, Lee Raffel, I Hate Conflict! Seven Steps to Resolving Differences with Anyone in Your Life, →ISBN, page 260:

     The Wilson family had been sorely conflicted because each member had gone off in his or her own direction, thinking that they were all lone gunmen.

• maverick
• rogue

• march to the beat of a different drum
• scapegoat