MILL SHOALS, Ill.—Authorities in two states are searching for a gunman who killed an eastern Illinois deputy early Wednesday and is suspected in a carjacking in neighboring Missouri a couple of hours later. The Wayne County Sheriff’s Office said in a Facebook post that Deputy Sean Riley responded to a motorist assist call on Interstate 64 near Mill Shoals around 5 a.m. Wednesday. A second officer who arrived at the scene found Riley dead. The deputy’s squad car was later found abandoned on I-64. The search for the suspect extended to St. Peters, Missouri, where police believe a man involved in a shooting and carjacking shortly after 7 a.m. Wednesday at a QuikTrip convenience store was the same person who killed the deputy. St. Peters police spokeswoman Melissa Doss said in an email that “there was evidence at the QuikTrip scene which indicates the suspect was also involved in the …