On March 8, 1971, burglars broke into an FBI office outside Philadelphia and stole thousands of files, exposing a covert campaign to spy on anti-war activists and other dissidents the law enforcement agency suspected of subversive behaviour. After the embarrassing break-in, FBI director J. Edgar Hoover ordered hundreds of agents to try to catch the perpetrators. Despite all its resources, the agency couldn't find them. While the case floundered, the incriminating documents surfaced in newspapers nationwide, disclosing a dark period in the FBI's history and humbling the powerful Hoover. The stolen material was the first glimpse of an agency operation called Cointelpro — an illegal and secret surveillance programme targeting Americans, and one that used dirty tricks and smear tactics. On Tuesday, some of the burglars involved in the break-in were finally identified, in a book by former reporter with The Washington Post , Betty Medsger, who first wrote about the stolen documents in 1971. Because a statute of limitations has long passed, those responsible cannot be prosecuted. The revelation rekindles interest in a period in the country's history when Americans fiercely debated government intrusions in the name of rooting out supposed threats. The book, The Burglary , comes as a similar, contentious debate is taking place in the United States about privacy in the wake of former contractor Edward Snowden's disclosures about National Security Agency surveillance programmes. "We hope that by coming forward today we can remind Americans of the abuses that unchecked police power can lead to, and contribute in some small way to the on-going public debate over these recurring issues," said Keith Forsyth, 63, an electrical engineer who, with seven others, executed the burglary. They suspected that the FBI was involved in questionable tactics, but needed evidence. The leader of the group was William Davidon, a physics professor at Haverford College in Pennsylvania who turned to some of his trusted associates for help. The group gave itself a name: the Citizens' Commission to Investigate the FBI. And so it did. Much of the planning took place at the house of Bonnie and John Raines in Philadelphia. On the night of a Muhammad Ali-Joe Frazier world title fight, they broke into the FBI office and stole thousands of documents. The FBI played it down at first, but two weeks later, Medsger, who had covered anti-war protests in Philadelphia but had since moved to The Washington Post , received a large envelope with 14 FBI files. On March 25, her first expose appeared on the front page of the Post . Reporters eventually figured out that these documents were the underpinning of Cointelpro. One document described how the agency wanted to "enhance paranoia and let the people know the FBI was behind every mailbox", Medsger said. The FBI closed the burglary case in 1976. Medsger said the agency narrowed hundreds of potential suspects to seven, but only one, John Raines, was from the Citizens' Commission to Investigate the FBI. Speaking on Tuesday, John Raines said: "Hoover lost. Freedom won."