As protesters around the country have marched against police brutality and in support of the Black Lives Matter movement, activists have spotted a recurring presence in the skies: mysterious planes and helicopters hovering overhead, apparently conducting surveillance on protesters. A press release ... revealed that the Drug Enforcement Agency and U.S. Marshals Service were asked by the Justice Department to provide unspecified support to law enforcement during protests. A few days later, a memo obtained by BuzzFeed News ... revealed that shortly after protests began in various cities, the DEA had sought special authority from the Justice Department to covertly spy on Black Lives Matter protesters on behalf of law enforcement. Both the DEA and the Marshals possess airplanes outfitted with so-called stingrays or dirtboxes: powerful technologies capable of tracking mobile phones or, depending on how they're configured, collecting data and communications from mobile phones in bulk. That data can be used to identify people - protesters, for example - and track their movements during and after demonstrations, as well as to identify others who associate with them. They also can inject spying software onto specific phones. Stingrays are routinely used to target suspects in drug and other criminal investigations, but activists also believe the devices were used during protests against the Dakota Access pipeline, and against Black Lives Matter protesters over the last three months.