We’ve already seen drones used for criminal purposes, such as surveying a potential robbery location and delivering drugs into prisons, but the FBI has just revealed how they were used to disrupt a hostage raid last winter.

Defense One reports that Joe Mazel, the head of the FBI’s Operational Technology Law unit, recounted the incident at the AUVSI Xponential conference in Denver, Colorado.

Mazel told attendees that an FBI hostage rescue team had taken up an elevated position to assess a situation outside of an undisclosed major US city. But it wasn’t long before they heard the sound of an approaching fleet of drones, which made a series of “high-speed low passes at the agents in the observation post to flush them.”

“We were then blind,” said Mazel, meaning the agents lost situational awareness of the target. “It definitely presented some challenges,” he added.

While the case is classed as being law-enforcement sensitive, Mazel was able to provide a few details. The suspects, anticipating law enforcement’s arrival, had brought drones to the scene in backpacks. Not only were they able to obstruct the agents by buzzing them, but the drones also sent video footage back to other gang members via YouTube.

“They had people fly their own drones up and put the footage to YouTube so that the guys who had cellular access could go to the YouTube site and pull down the video,” explained Mazel.

As increasingly cheaper and more portable models become available, the use of drones among gangs to surveil police departments and identify witnesses is increasing. They’re becoming a vital tool for criminals, who use them for everything from smuggling, to burglaries, to monitoring authorities’ movements. They’ve even been weaponized with guns and explosives, something that the upcoming Federal Aviation Administration reauthorization bill wants to make illegal. It also requires drone pilots operating the devices outside of their line of sight to remotely identify themselves to law enforcement.