spying on Americans

The F.B.I. 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.

The National Security Agency and the Central Intelligence Agency have explored using link analysis to trace patterns of communications sometimes two, three or four people removed from the original targets.

Such link analysis is misused to establish tenuous links to people who have no real connection to terrorism but may be drawn into an investigation nonetheless.