FBI director Robert Mueller last month told a Senate Judiciary Committee hearing the the bureau has been using drones for domestic surveillance. Mueller, however, did not offer any specifics, promising instead that the usage was "very minimal." Nevertheless, he told the committee he would submit more information later.
An unclassified letter sent by the FBI in response to questions sent by Rand Paul reports the bureau has used drones since 2006, in a total of "eight criminal cases and two national security cases." The only specific case offered was that of the week-long hostage situation involving a six-year-old girl in Alabama earlier this year. The FBI also claimed the drones were not equipped with any kind of weapons nor were they conducting "bulk" surveillance.
While the FBI said it would seek a warrant to use a drone if it involved breaching a "reasonable expectation of privacy," it said it had not needed to seek a warrant in any of its drone use so far, relying instead on internal legal advice (a favorite approval process of the executive branch). In a follow-up letter sent by Paul today, the senator asks the FBI for specifics on how the bureau defines a "reasonable expectation of privacy" and any "guidance documents," like legal memos and field manuals, that would expand on what the FBI considers a reasonable expectation of privacy. You can read Paul's full letter here.