A federal judge in San Francisco recently excoriated the government over its improper methods in searching one suspect's cell phone and in the use of a stingray to find an alleged co-conspirator. Prosecutors say the two men, Donnell Artis and Chanta Hopkins, were engaged in credit card fraud and also illegally possessed firearms, among other pending charges that also involve four other people. The crux of the issue is that, in April 2016, an FBI agent sought and obtained two warrants from an Alameda County Superior Court judge: one to search Artis' phone and another to deploy a stingray to locate Hopkins.
As Ars has reported for years, stingrays are in use by both local and federal law enforcement agencies nationwide. The devices determine a target phone's location by spoofing or simulating a cell tower. Mobile phones in range of the stingray then connect to it and exchange data with the device as they would with a real cell tower. Once deployed, stingrays intercept data from the target phone along with information from other phones within the vicinity—up to and including full calls and text messages. At times, police have falsely claimed that information gathered from a stingray has instead come from a confidential informant. However, California law does not allow state judges to sign off on warrants for federal agents, something that this particular FBI agent, Stonie Carlson, apparently did not know.