A good 42 years before Edward Snowden pilfered secret National Security Agency documents detailing broad government surveillance, a band of eight antiwar protesters broke into an FBI field office in Media, Pa., and stole boxes of documents. The internal FBI memos and records, once sent to journalists, exposed widespread counterintelligence efforts by J. Edgar Hoover's FBI designed to crush America's antiwar and civil rights movements.

The thieves were never caught, despite the efforts of some 200 FBI agents, and they didn't reveal themselves. Betty Medsger, a former Washington Post reporter who wrote the first article based on the leaked FBI documents, finally discovered the identities of the burglars, and she persuaded five of them to come forward in her new book, The Burglary: The Discovery of J. Edgar Hoover’s Secret FBI, out this week.

The man who hatched the plan, Haverford College physics professor William C. Davidon, died last year. Retro Report got three of the surviving burglars — former taxi driver Keith Forsyth and academics John and Bonnie Raines, a couple then raising a young family — to talk on video about their raid on the FBI office.

Their story, told in the video above, is a good tale in its own right, filled with the clever plotting — they broke in on March 8, 1971, during the world heavyweight boxing match between Joe Frazier and Muhammed Ali — and the mundane travails of amateur burglars. But the documents they sent to the press, under the name the Citizens' Commission to Investigate the FBI, changed history.

The records revealed FBI efforts to spy on and infiltrate the antiwar movement and destroy it by sowing paranoia among its members. One document with the mysterious word "Cointelpro" led to the discovery of a dissent-quashing FBI program — dubbed the Counterintelligence Program — that stretched back to 1956 and included an effort to blackmail Martin Luther King Jr. into killing himself. "It wasn't just spying on Americans," Loch K. Johnson, a former aide to Sen. Frank Church (D-Idaho), tells The New York Times. "The intent of Cointelpro was to destroy lives and ruin reputations."

These revelations led to the Church Commission into domestic spying abuses, broad reforms at the FBI and CIA, and the creation of the Foreign Intelligence Surveillance Act (FISA) court now at the center of Snowden's revelations. What makes the 1971 FBI break-in all the more remarkable is that, as Retro Report puts it, it is "the greatest heist you've never heard of." And for 43 years, its protagonists were happy to let their work quietly speak for itself.