FOX LAKE, Ill. (AP) — Police with helicopters, dogs and armed with rifles were conducting a massive manhunt in northern Illinois on Tuesday after an officer was shot and killed while pursuing a group of suspicious men.

An emotional Fox Lake Mayor Donny Schmit described the slain officer, Lt. Charles Joseph Gliniewitz, as a personal friend, a three-decade member of the department and a father of four sons.

"We lost a family member," Schmit said of the 52-year-old officer known around town as "GI Joe." ''His commitment to the people of this community has been unmatched."

Authorities said Gliniewitz radioed in to tell dispatchers he was chasing three men on foot in the city of Fox Lake, 55 miles north of Chicago. Communication with him was lost soon after, said Lake County Sheriff's Office spokesman Sgt. Christopher Covelli.

"His backup arrived shortly thereafter and found him injured with a gunshot wound," Covelli said. "The officer has succumbed to his injuries and passed away."

Undersheriff Raymond Rose told the Chicago Tribune that the officer had also been stripped of his gun and other equipment.

Police and other law enforcement, some of them in military-style camouflage, were seen taking up positions on rooftops and along railroad tracks, scanning the terrain with rifle scopes and binoculars. Others leaned out of helicopters with weapons at the ready.

Nearby Grant Community High School was placed on hard lockdown with children and staff instructed to say hidden and away from windows, and Schmit said that other schools were also put on lockdown, as staffers went from room to room to make sure the children were safe.

At the same time, authorities urged residents throughout the area to stay in their home while they conducted a search for three men, two of them white and the other black, using bloodhounds on the ground and helicopters above.

Service of a local commuter train was halted and residents who wanted to take their dogs outside to relieve themselves were told to stay in their homes — with the job of walking the dogs handled by police officers.

Around Fox Lake, residents expressed their own grief over the death of the immensely popular Gliniewitz.

"This particular officer is a pillar in my community and definitely going to be missed, and (he) touched so many lives," said Gina Maria, a 40-year-old teacher who lives in the community.