CHICAGO — With helicopters buzzing overhead and police dogs searching on the ground, the authorities in northern Illinois conducted a sprawling manhunt Tuesday evening for three people suspected in the fatal shooting of a Fox Lake police lieutenant that morning.

The lieutenant, Charles Joseph Gliniewicz, a 30-year police veteran with four sons, died after an encounter with three males Tuesday morning in Fox Lake, the authorities said. Fox Lake, a community of 10,500 people, is roughly halfway between Chicago and Milwaukee.

Dozens of state and federal agents joined local police officers in the search. A no-fly zone was ordered over Fox Lake, schools were on lockdown, and some commuter trains were stopped.

“Our community is having a very difficult time, and the coming days will be even more difficult as we remember him,” Mayor Donny Schmit said.