All that stood between Keith Forsyth and the thousands of confidential papers belonging to the Federal Bureau of Investigation was one simple door.

It was early 1971, and war protestor Forsyth had been tasked with picking the lock that kept the FBI’s satellite office in Media, Pennsylvania, secure. Inside was believed to be evidence that the organization had been engaging in unlawful surveillance of private citizens, infiltrating civil rights groups, and spreading a message of paranoia. Forsyth’s allies, an informal assembly calling themselves the Citizens Commission to Investigate the FBI, planned to offer proof by disseminating the papers to media outlets all over the country.

A cab driver, Forsyth had rallied against the Vietnam war, but his activism had been limited to demonstrations. He was not a skilled locksmith. He took a correspondence course on lock picking, practiced, and waited until the world was busy watching Muhammad Ali fight Joe Frazier to break into the bureau’s offices. What he and the “Commission” found would lead to congressional hearings and widespread changes over the FBI’s alarming conduct.

But first, Forsyth had to deal with the lock—one the FBI had changed just before he snuck in.

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The idea to steal J. Edgar Hoover’s secrets originated with William Davidon, a well-known activist and physics professor at Haverford College in Haverford, Pennsylvania. Davidon had participated in his share of rallies, but felt no significant change would be effected until the general public could see for themselves what he and other protestors had long suspected—that the FBI had been engaging in unchecked surveillance and sabotage of any group they considered subversive.

In fall 1970, eight men and women had been caught attempting to enter an FBI office in Rochester. All eight were tried and convicted, but the incident led Davidon to pursue a similar plan. How could it be different? For one thing, his group wouldn’t attempt to infiltrate a field office in a major city. Philadelphia was out. But Media, with its quaint FBI arm in an office building that kept banker’s hours, was low on security.

Davidon enlisted John and Bonnie Raines, a married couple, for the plan; he also brought in Forsyth, who had some mechanical knowledge and would make for a quick study when it came to breaching the door. The group was joined by four co-conspirators; all of them spent months learning about the comings and goings of the various office residents.

To case the interior, Bonnie Raines tucked her long hair under a cap and posed as a college student looking to know more about opportunities for women in the FBI. While there, she noticed the filing cabinets were kept unlocked, and that the office only had two entry doors.

On March 8, 1971, Forsyth stepped quietly through the halls of the building. When he bent over to inspect the lock, he found it had been changed since he had last passed through. He went over to the second entrance door and used a crowbar to slowly pry it open. Because the door wasn’t in use, a filing cabinet had been moved against it; when Forsyth began to push against the door, the filing cabinet started to tip over. Realizing that if it hit the ground it would wake the entire building, he ran to his car and grabbed a jack stand (later he told CSPAN, “thank goodness this was 1971 ... when they had real jacks in cars”) that he used as a pry bar. For the next 20-plus minutes, he pushed the cabinet slowly along the floor until he could finally get in.

The Citizens Commission ransacked the offices, filling up as many briefcases as they could with documents and being careful not to leave any fingerprints. Driving to a farmhouse an hour away, they spent days combing through the files, occasionally stopping to hold up a piece of incriminating paper. While the Commission suspected the FBI was abusing its powers, the world was about to be surprised by how far that unchecked privilege had gone.

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Betty Medsger was one of several journalists to receive a semi-anonymous package on March 23. A reporter for The Washington Post, Medsger noticed the return address was Media, Pennsylvania. Inside were 14 pages of photocopied documents detailing the FBI’s impropriety. One brief read that the common goal of the Bureau should be to “enhance the paranoia” and to make dissenters believe “there is an FBI agent behind every mailbox.”

The mission statement was mild compared to their actions. As Medsger and other journalists from the Los Angeles Times and The New York Times would learn, the FBI had been persistent in keeping tabs on “militant negroes,” mandating that every agent have at least one informant leaking information about civil rights groups; anyone who had written and signed a letter to a newspaper protesting the war was pegged for investigation; even a Boy Scout troop in Idaho was under surveillance because the scoutmaster may have been planning to take the troop to the Soviet Union.

Then-Attorney General John Mitchell implored the Post not to publish information from the papers, insisting they were stolen property and a matter of national security. After hours of deliberation, the newspaper’s staff ran with the story the following day. Before long, the national news media had been blanketed with irrefutable proof the FBI had overstepped its bounds.

The Citizens Commission had only stumbled across the proverbial iceberg tip. In 1973, NBC News reporter Carl Stern became intrigued by a small stub that referred to a project called COINTELPRO, Hoover’s name for the agency’s covert domestic spy operations. After a legal struggle, the FBI released 50,000 pages of files that were even more incriminating. Among them: an anonymous letter sent to Martin Luther King, Jr. in 1964 advising him that his alleged infidelity would be revealed if he continued his activism.

“King, there is only one thing left for you to do,” the note read. “You know what it is.” The message, which was implying King should take his own life, had been a product of the FBI.

In 1976, Congress held hearings to discuss the leak, the first to ever explore the inner workings of a government intelligence agency. Expressing outrage at Hoover's behavior—in which they noted legal restrictions had been ignored—the hearings eventually resulted in the Foreign Intelligence Surveillance Act (FISA) of 1978 that required a warrant to monitor a private citizen.

Despite Hoover putting more than 200 agents on the case, only one member of Davidon’s crew was even considered a possible suspect. When the crime’s statute of limitations ran out in 1976, the group still swore to keep the operation a secret, fearing some unknown retribution might still be possible. It wasn’t until Medsger met with the Raineses in 1989 that the couple confessed their involvement, and it wasn’t until 2014 that most of the others went public, in part to support the actions of document leak target Edward Snowden.

With no arrests made, the FBI officially closed the case on March 11, 1976. They had compiled over 33,000 pages relating to their investigation of the break-in. Presumably, they bothered to lock their filing cabinets this time.