CHICAGO—A federal indictment filed Thursday charges a 28-year-old Chicago man in connection to a drive-by shooting of three undercover law enforcement officers, and it says the suspect told authorities he mistook the officers for rival gang members. Eugene “Gen Gen” McClaurin is charged with one count of using a dangerous and deadly weapon to assault a special agent from the U.S. Bureau of Alcohol, Tobacco, Firearms, and Explosives. Charging documents accuse McClaurin of shooting the other ATF agent and a Chicago task-force officer, though the charge pertains to one agent. It is likely other charges will follow. A conviction on the one count carries a maximum 20-year prison sentence. After his arrest Wednesday morning, McClaurin told investigators a friend had warned him rival gang members were in the area in a vehicle similar to the unmarked vehicle the two ATF agents and task-force officer were in, according to the indictment. …