The police officer who was fatally shot Tuesday outside of Chicago has been identified as a longtime veteran of the local police force, the mayor said. Lt. Joseph Gliniewicz was named as the officer who was killed in Fox Lake, Illinois. The manhunt for three suspects believed to be involved in the shooting is underway and involves state and local officials, Lake County Sheriff's Department Det. Chris Covelli said."Not only did Fox Lake lose a family member but I lost a very close friend," Fox Lake Mayor Donny Schmit said at a news conference.He said that Gliniewicz was a father of four boys and had worked for the force for more than three decades."Many residents here knew him as G.I. Joe," Schmit said.The deadly shooting is believed to have happened after the officer sent a radio message saying that he was chasing after three men, authorities said.The incident started at 7:52 a.m. Tuesday when the officer said via radio that he was pursuing three men, according to a Lake County Sheriff's Office spokesman.Police lost communication with the officer after his radio message, and a backup officer found him injured, police said.The suspects remain at large, the Lake County Sheriff's Office spokesman said. Canine crews are being used as well as officers on foot and in helicopters in the search.The FBI is assisting local authorities and a representative told ABC News that they have agents on the ground. Agents with the Bureau of Alcohol, Tobacco and Firearms are already at the scene and the U.S. Marshals confirmed to ABC News that members of its Great Lakes Fugitive Task Force were headed to the scene.The Federal Aviation Administration established a temporary flight restriction over the search zone, and it is scheduled to be in effect until Wednesday afternoon.Fox Lake is a suburb about 60 miles north of central Chicago