Correction: An earlier version of this obituary incorrectly identified Mr. Judge in the photo caption and in the text as “Mr. Gray.” The article has been corrected.

“I tell people you can call me a conspiracy theorist if you call everyone else a coincidence theorist,” Mr. Judge, who died at 66, once remarked. (Bob Gray)

John P. Judge, an independent researcher who tirelessly amassed and disseminated evidence supporting alternative explanations — some called them conspiracy theories — for President John F. Kennedy’s assassination, the 9/11 terrorist attacks and other historic events, died April 15 at a nursing facility in the District. He was 66.

Through years of investigation and activism, Mr. Judge developed a devoted following in the community of skeptics who question official or commonly accepted narratives of the past. He co-founded and directed the Coalition on Political Assassinations, an organization whose activities include investigating the deaths in the 1960s of John Kennedy, his brother Robert F. Kennedy, civil rights leader Martin Luther King Jr. and black nationalist leader Malcolm X. News outlets, with some frequency, featured Mr. Judge and his work.

He turned his Washington home into a repository of thousands of volumes and documents on political assassinations and other matters, supporting himself over the decades through odd jobs and fundraising work. He was once described as a “professional conspiracist,” but he considered himself an “alternate historian,” according to his Web site,

“I tell people you can call me a conspiracy theorist if you call everyone else a coincidence theorist,” Mr. Judge quipped to the publication National Journal.

His most noted work involved President Kennedy’s death in Dallas on Nov. 22, 1963. Like legions of others doubters labeled conspiracy theorists, Mr. Judge rejected the Warren Commission’s finding that Lee Harvey Oswald had been the lone gunman.

Mr. Judge’s working theory, he told interviewers, was that the assassination had been organized by the Joint Chiefs of Staff. “I don’t think this is an insoluble parlor mystery,” he once told the Dallas Morning News. “I don’t think we are just flailing in the dark.”

Mr. Judge helped organize in Dallas annual commemorations of Kennedy’s death. He and others gathered on the grassy knoll, the spot where another gunman, according to some theories, was stationed. Those memorials became the subject of controversy last year, when Dallas marked the 50th anniversary of Kennedy’s death.

After contentious discussions with event organizers, the Coalition on Political Assassinations agreed to hold its ceremony in a parking lot several blocks away from the usual spot, which was restricted to ticket-holding participants.

“We’ll be here,” Mr. Judge had said. “We may have to crawl through the sewer system and pop our heads up where the assassin was, but we’ll be here.”

In his work regarding more recent history, Mr. Judge cofounded the 9/11 Citizens Watch to monitor the operations of the official 9/11 Commission, the independent and bipartisan body created by congressional legislation to prepare a full account of the attacks.

He briefly worked as an assistant to then-U.S. Rep. Cynthia McKinney (D-Ga.), who was widely rebuked when she suggested that President George W. Bush’s administration might have had advance notice of the terrorist strike.

Former congressman Dennis J. Kucinich (D-Ohio), who met Mr. Judge during his Capitol Hill employment, described him as “brilliant” and said he had been “very impressed” by Mr. Judge’s research abilities.

“I may not have agreed with him on everything,” Kucinich said of Mr. Judge in an interview, but he was “an original, independent thinker and someone who immersed himself in hidden history.”

At the time of his death, Mr. Judge was working toward the establishment in Washington of the Museum of Hidden History, which would include an archive and library. Among other missions, according to its Web site, it would “inform and educate the public about little-known aspects of local, national and international history.”

“It erodes the rational approach when you talk of conspiracies involving a small cabal in a board room controlling world history,” Mr. Judge once told the Boston Globe. “But it’s a common human trait to want an explanation for all the unexplained things that are happening — some kind of grand unified theory.”

John Patrick Judge was born Dec. 14, 1947, in the District, and he grew up in Falls Church, Va. Both his parents worked at the Pentagon.

Mr. Judge graduated in 1970 from the University of Dayton in Ohio, where he studied theology and where he recalled being obliged to participate in the Reserve Officers’ Training Corps. He later joined the American Friends Service Committee as a draft counselor during the Vietnam War.

In the District, Mr. Judge became what the Washington City Paper described as “the voice of military dissent in D.C. public schools.” He sought to counter military recruiting efforts by attending career days and informing students of what he alleged were discrimination and deprivation of rights within the military.

Mr. Judge’s survivors include his companion of four years, Marilyn Tenenoff of York Haven, Pa. She said that Mr. Judge had a stroke in March but that the cause of death had not been determined. The D.C. medical examiner’s office had not ruled on the case, according to a spokesman.

Tenenoff said she plans to request an outside review of the autopsy report, when it is available, to assuage the concerns of anyone who may doubt its accuracy.