“[I]f the Tsarnaev brothers had been detected by a drone,” would that evidence be inadmissible in court? , brought up the FBI’s shutdown and search for the Tsarnaev brothers in Boston among his first questions to the panelists.

In the immediate aftermath of the bombings, street cameras recorded footage of the event, Rep. Trent Franks, R-Ariz., said, later in the hearing. “Does it matter to you constitutionally if those images came from a street camera or unmanned surveillance?”

Christopher Calabrese, legislative council at the American Civil Liberties Union, said that warrants should be required for all law enforcement drone work, to prevent mass surveillance by the government. But his fellow experts argued that a blanket warrant requirement could have serious drawbacks.

“Suppose that law enforcement is monitoring a traffic accident [by drone] and on the sidewalk a terrible assault takes place,” said panelist John Villasenor, a non-resident senior fellow at the Brookings Institution, a non-profit policy think tank, and a professor at UCLA. “Suppose the video evidence is the only evidence,” he added, suggesting that a drone-approved for traffic monitoring would not be able to provide that evidence against the perpetrator of that crime.