Last Updated Sep 2, 2015 9:07 AM EDT
An urgent manhunt is being conducted across northern Illinois for three men suspected of killing Fox Lake olice Lt. Charles Joseph Gliniewicz.
While detectives have told the public to report suspicious activity, those suspects have only been identified as two white men and one black man, making it difficult to know exactly who to look out for, reports CBS News correspondent Anna Werner.
Gliniewicz was 29 days from retirement when he was shot on the job.
He was walking toward three men Tuesday morning, radioing dispatch that he was responding to "suspicious activity," then dispatch lost contact with him.
The officer sent as backup found Gliniewicz on the ground near a marsh area. He died at the scene and his gun was found nearby, the Chicago Tribune reports.
The shooting touched off an aggressive manhunt. A half-dozen helicopters took off and snipers staked out on rooftops, while SWAT teams in tactical gear scoured 2 square miles, looking for the three suspects.
Lake County Sheriff's Office spokesman Sgt. Christopher Covelli said Wednesday morning that the search area had widened.
"We had over 400 police officers out here yesterday. We had over 45 canine units and numerous aircraft," Covelli said, adding that officers would now conduct "saturation patrols" in a wider area.
Several school districts in the search area canceled Wednesday classes.
"I lost a very dear friend," Fox Lake Mayor Donny Schmit said.
He said the village of about 10,000 is in mourning.
"Many residents in here knew him as 'G.I. Joe' and remember him as someone deeply committed to Fox Lake, to the profession and his fellow officers," Schmit said.
Gliniewicz was a 30-year veteran of the Fox Lake Police Department and a married father of four sons.
He is the first on-duty officer killed in Lake County since 1980.
"He was a lot of everything to everybody, everybody was just safe around Joe," friend Tammy Rivette said.
The 52 year-old served as an adviser, mentoring aspiring police officers in the city's Explorer program.
"He meant something to this community," one of his trainees Zachary Point said. "He made it a better place; you felt comfortable."
Murders are rare in Fox Lake and according to state police, there haven't been any reported in several years.
The community will hold a vigil for their fallen lieutenant Wednesday night at 6 p.m.