A federal judge in Mississippi ruled Wednesday that “tower dump” warrants are unconstitutional, declining to reverse a lower court decision refusing the government’s request to obtain the search warrants in a series of violent crime investigations. A “tower dump” involves cellphone companies providing law enforcement with access to the time and location data of all mobile devices connected to specific cell towers during a designated time window. Law enforcement had sought approval for several of these search warrants as part of criminal investigations into gang-related activity in the Jackson, Miss., area last year, arguing the data could help identify all...