Forty years ago, two unanswered questions loomed over the murky history of the FBI’s infamous pursuit of Rev. Martin Luther King Jr.: who were the top-secret informants who had fingered King’s confidante Stanley Levison as a former top Communist functionary, and who was the Atlanta informant who had burrowed into the headquarters of King’s Southern Christian Leadership Conference?

Across 1979 and 1980, I pursued those two mysteries. On the first, Emory University scholar Harvey Klehr provided a crucial assist; on the second, thousands of pages of imperfectly redacted documents sent to me pursuant to the Freedom of Information Act offered decisive clues. When I telephoned former FBI intelligence chief Charles “Chick” Brennan to cite brothers Jack and Morris Childs as the FBI’s top Communist sources, Brennan’s response confirmed Klehr’s clue: “How do you know those names?” Within 24 hours, FBI counterintelligence unit chief Michael Steinbeck called to say he was coming to visit me.

Steinbeck’s message was clear: should I proceed to publish the Childs brothers’ names, and that of former SCLC comptroller James A. Harrison as the FBI’s mole close to King, the Bureau would seek my indictment under the Espionage Act of 1917. I declined proffered meetings with President Jimmy Carter and then his successor, Ronald Reagan. In September 1981, my book “The FBI and Martin Luther King, Jr.”, was published, and The Washington Post named the Childs brothers on its front page while The Atlanta Journal did the same with Harrison. The FBI’s threat evaporated, but being told one should not publish accurate, historically important information may have had a formative effect upon me.