Earlier this year, the US Federal Bureau of Investigation (FBI) publicly revealed for the first time in a hearing that it has been using drones to conduct surveillance operations inside the country, a striking admission, given that domestic drone is a subject of intense debate and there's still not a clear set of rules governing the practice. Now, under prodding from Senator Rand Paul (R-KY), the FBI has finally offered a few more details about its use of drones, namely, in how many cases it's deployed them, and its rationale for not seeking a search warrant. "Since late 2006, the FBI has conducted surveillance using UAVs [unmanned aerial vehicles] in eight criminal cases and two national security cases," wrote Stephen D. Kelly, the FBI's assistant director for the Office of Congressional Affairs, in a letter to Paul. In a footnote added to this statement, Kelly explains drones were also approved in three other cases, but the FBI didn't use them.

"there has been no need for the FBI to seek a warrant or judicial order."

Kelly touts the success of the FBI using a surveillance drone in one in highly publicized case, in which it helped rescue a five-year-old boy from a kidnapper back in April. He notes that none of the drones the FBI uses are armed with any weapons, lethal or otherwise, and that drone use "must be approved by senior FBI management at FBI headquarters and in the relevant FBI field office." But the new information raises many more questions than it answers, namely: how many different times have the FBI actually flown drones on each of these cases? For how long? What specific information was captured by the drones during flight? And, what types of drones were used?

Then there's the issue of the Fourth Amendment, which protects US citizens from unreasonable search and seizure, and which typically means that law enforcement has to get a warrant to conduct a search. Kelly, though, reveals in his letter to Paul that the FBI hasn't actually obtained a warrant for any of its drone surveillance operations so far. "To date, there has been no need for the FBI to seek a warrant or judicial order in any of the few cases where UAVs have been used," Kelly writes, saying in all of the cases, the people surveilled had no "reasonable expectation of privacy."

But that rationale highlights a larger ambiguity about drone use on American soil, which is that there's great uncertainty over when aerial surveillance of any kind is legal. The Supreme Court ruled in 1989 that it was okay for a police department to fly a manned helicopter 400 feet above a suspect's property without getting a warrant, but it's unclear if flying any closer is constitutional. Paul, for his part, says he's not satisfied with the FBI's explanations for warrantless drone use, and has sent the agency another letter saying he's concerned that it's "overbroad," and asking for more information. In the meantime, the new FBI disclosures provide at least a bit more insight into how fast surveillance practices are changing, and how the legal system has yet to catch up.