When a group of anti-war activists broke into an FBI office in Media, Pennsylvania, on 8 March 1971 they hoped that they would be hitting the bureau’s overweening director, J Edgar Hoover, where it hurt most. They would grab whatever documents they could find and in that way expose the culture of Big Brother illegality that Hoover had created.

The plan went better than they could ever have dreamed. Among a huge stash of confidential documents the group retrieved were secrets about the FBI’s blanket surveillance of the peace and civil rights movement, the tactics of disinformation and deception the bureau used to silence protesters and even an attempt by agents to have Martin Luther King commit suicide.

Yet despite a massive police hunt, into which Hoover threw 200 agents, the perpetrators of that audacious break-in have never been identified. They had carried out the perfect political crime, and got away scot-free.

Now, almost 43 years later, five of the eight ordinary citizens who carried out the break-in have finally come forward and revealed themselves. They have co-operated with Betty Medsger, the former Washington Post journalist who was the first to publish the revelations contained in the stolen documents and who has written a new book on the saga called The Burglary: The Discovery of J Edgar Hoover’s Secret FBI.

In a telephone press conference given by three of the self-styled Citizens’ Commission to Investigate the FBI on Tuesday, Keith Forsyth, who acted as the lock-picker on that fateful day, tried to answer the question of why they decided to come out of the shadows so many years after the event. He said that following the raid on the documents the eight had had no desire to identify themselves as “the prospect of enduring harsh punishment in prison for revealing the immoral acts of our government was not appealing.”

Today the significance of what they did had renewed public interest, he added, in the wake of the Edward Snowden leaks of National Security Agency documents. “Our government is again conducting mass surveillance of Americans and again lying to Congress. We hope that by coming forward we can contribute in some small way to a debate that is essential for the health of our democracy.”

The perpetrators of the burglary have received legal advice that they can not now be prosecuted: the statute of limitations for the “theft of government documents” charge that could have been brought by the Justice Department expired in 1976. David Kairys, a civil rights attorney who has advised the group, said that the Espionage Act – used aggressively under the Bush and Obama administrations to pursue leakers such as Chelsea Manning and Snowden – would not have applied as there was no espionage involved in the Media case. Besides that, in 1971 a breach of the act carried a 10-year statute of limitations.

In an article for the Guardian, another of the culprits, Bonnie Raines, said that she too drew parallels between their act four decades ago and the Snowden leak revealing NSA blanket surveillance. “I think Snowden's a legitimate whistleblower, and I guess we could be called whistleblowers as well,” she writes.

The Media, Pennsylvania, burglary is credited with having led to the unraveling of the vast and cavalier web of surveillance that Hoover built up over many years. The Washington Post ran with Medsgers stories despite the efforts of the Nixon administration to strong-arm the newspaper into foregoing publication.

The most incendiary element of the stolen documents was the existence it revealed of a programme called Cointelpro – or Counterintelligence Program – a massive effort by the FBI to infiltrate and disrupt the peace, civil rights and black power movements and put many of their leaders under surveillance. One notorious letter sent by the FBI to Martin Luther King contained materials relating to his extra-marital sexual activity intended to blackmail him into suicide, with a note that said: “King, there is only one thing left for you to do. You know what it is.”

Medsger said that the revelations had shocked Americans. “The documents revealed massive surveillance particularly on African Americans. FBI agents were required to have at least one informant reporting to them on the actions of black people every week.”

She added that Cointelpro had been “one of Hoover’s worst operations” and that the overall impact of the released documents had been to expose how the FBI was conducting “a secret war on dissent, primarily against anti-war activists and African Americans. The revelations ignited a national debate about surveillance that has been reignited by Edward Snowden’s revelations about the NSA.”

The Media files not only dramatically impacted Hoover and the FBI, they also had a seismic impact on the media landscape. The burglars posted anonymously packages of documents to a number of Congress members and to several newspapers including the Washington Post, the New York Times and Los Angeles Times.

Hoover, backed by President Nixon, made strident demands for the return of the documents, arguing they were stolen government property. Newspapers in the US had never before had to deal with the conundrum of what to do with leaked documents that had been procured illegally by people not in official positions.

Katharine Graham, who had only been officially enshrined as publisher of the Washington Post two years before the break-in, was the only one to stand up to Hoover and Nixon and publish despite their protestations. The New York Times and the Los Angeles Times are both believed to have returned all the documents to the FBI, though they did report the story after the Post had gone ahead.

• This article was amended on 7 January 2014. An earlier headline indicated that the burglars were just now coming forward with the stolen documents. They were simply revealing their identities