WASHINGTON – The FBI cast a much wider net in its terrorism investigations than it has previously acknowledged by relying on telecommunications companies to analyze phone-call and e-mail patterns of the associates of Americans who had come under suspicion, according to newly obtained bureau records. The documents indicate that the Federal Bureau of Investigation used secret demands for records to obtain data not only on individuals it saw as targets but also details on their “community of interest” – the network of people that the target in turn was in contact with. The bureau recently stopped the practice in part because of broader questions raised about its aggressive use of the records demands, which are known as national security letters, officials said Friday after being asked about it. The community-of-interest data sought by the FBI is central to a data-mining technique intelligence officials call link analysis. Since the attacks of Sept. 11, 2001, American counterterrorism officials have turned more frequently to the technique, using communications patterns and other data to identify suspects who may not have any other known links to extremists. The concept has strong government proponents who see it as a vital tool in predicting and preventing attacks, and it is also thought to have helped the National Security Agency identify targets for its domestic eavesdropping program. But privacy advocates, civil rights leaders and even some counterterrorism officials warn that link analysis can be misused to establish tenuous links to people who have no real connection to terrorism but may be drawn into an investigation nonetheless. Typically, community-of-interest data might include an analysis of which people the targets called most frequently, how long they generally talked and at what times of day, sudden fluctuations in activity, geographic regions that were called, and other data, law enforcement and industry officials said. The FBI declined to say exactly what data had been turned over. It was limited to people, phone numbers and e-mail “once removed” from the actual target of the national security letters, said a government official who spoke on condition of anonymity because of a continuing review by the Justice Department. The scope of the demands for information could be seen, for instance, in an August 2005 letter seeking the call records for particular phone numbers that had come under suspicion. The letter closed by saying, “Additionally, please provide a community of interest for the telephone numbers in the attached list.” The requests for such data showed up a dozen times, using nearly identical language, in records from one six-month period in 2005 obtained by a nonprofit advocacy group, the Electronic Frontier Foundation, through a Freedom of Information Act lawsuit that it brought against the government. The FBI recently turned over 2,500 pages of documents to the group. The boilerplate language suggests that the requests might have been used in many of more than 700 emergency or “exigent” national security letters. Earlier this year, the bureau banned the use of the exigent letters because they had never been authorized by law. The bureau declined to discuss any aspect of the community-of-interest requests because it said the issue was part of an investigation by the Justice Department inspector general’s office into national security letters. An initial review in March by the inspector general found widespread violations and possible illegality in the FBI’s use of the letters, but it did not mention the use of community-of-interest data. The government official who spoke on condition of anonymity said the FBI recently stopped asking the telecommunications companies for the community-of-interest data. The exact time of and reason for the suspension is unclear, but it appears to have been set off in part by the questions raised earlier this year by the inspector general’s initial review into abuses in the use of national security letters.160Want local news?Sign up for the Localist and stay informed Something went wrong. Please try again.subscribeCongratulations! You’re all set!