A police officer was shot and killed Tuesday north of Chicago, sparking a manhunt that stretched through much of the day and into the evening as local and federal authorities scoured a part of northern Illinois for suspects in the shooting.

Officials identified the slain officer as Lt. Charles Joseph Gliniewicz, who they said was known to many as “G.I. Joe.”

Gliniewicz, a police officer in Fox Lake, Ill., had radioed shortly before 8 a.m. that he was on foot chasing three suspicious subjects, Chris Covelli, a Lake County Sheriff’s spokesman, said during a morning news conference.

A short time later, after contact with Gliniewicz was lost, another officer found him with a gunshot wound, Covelli said. The three suspects were only described as two white men and a black man.

“Understandably, our officers are having a very difficult day today,” Fox Lake Mayor Donny Schmit said at a news conference Tuesday afternoon. “We lost a family member.”

Schmit said that Gliniewicz was a father of four and a decorated police officer.

“The coming days will be even more difficult as we remember him as a police officer, a father and a member of our community,” Schmit said.

[After Texas deputy’s death, a reminder of the increased anxiety felt by law enforcement officers amid protests]

The airspace immediately over the manhunt was shut down by the Federal Aviation Administration at the request of the Fox Lake Police Department, an FAA spokeswoman said. This restriction, which went into effect shortly after 1:30 p.m. local time, bars any flight under 3,000 feet above the ground level where the search is taking place.

Helicopters flew overhead during the manhunt, while police officers using search dogs scoured the ground below.

Fox Lake, a small village with about 10,000 residents, is a little more than an hour north of downtown Chicago.

“This should never happen,” Thomas Poulos, a retired Waukegan police officer who said he went to high school with Gliniewicz, told the Chicago Tribune. “Joey just loved his job.”

Schmit, the Fox Lake mayor, said that authorities would work going forward to reassure the community that they were safe as the investigation continued.

Grant Community High School was locked down Tuesday at the request of the Fox Lake police, school officials said.

“A police matter is occurring in the community and for the safety of our students and staff they have requested we remain locked down,” the school said in a statement online. It added that all students and staff remained safe during the lockdown.

One of the stations on the Metra commuter rail system was closed due to the search. Metra said that it had closed the Ingleside station on the Milwaukee District North line, which runs from Fox Lake to Chicago’s Union station.

Gliniewicz is the 24th police officer shot and killed by a suspect this year, according to the Officer Down Memorial Page, a nonprofit organization that tracks line-of-duty fatalities.

Four of these shootings have occurred over the past eight days. The latest shooting comes just days after a Texas sheriff’s deputy was gunned down while getting gas in suburban Houston, a killing that drew renewed attention to the tension law enforcement officials say they feel amid ongoing protests against how police use deadly force.

A Lake County under-sheriff told the Chicago Tribune that Gliniewicz was found stripped of his gun and other gear.

[President Obama: Violence against police ‘is completely unacceptable’]

In addition to local law enforcement agencies, the FBI said Tuesday it was aiding with the search. The Bureau of Alcohol, Tobacco, Firearms and Explosives said it had agents as well as dogs to participate in the search efforts.

The sheriff’s office in neighboring McHenry County said it was asked to provide officers, armored vehicles, a SWAT team and police dogs.

“Sending our thoughts and prayers to the Fox Lake Police Department, their families and friends and all the officers responding to assist with the shooting,” the office said in a statement.

Related:

Police officers experience fewer deaths these days — but increased tension

After arrest in ‘execution-style’ shooting of Texas deputy, a search for a motive

Nearly a quarter of the police officers shot and killed this year have been in Louisiana

This post has been updated. First published: 2:50 p.m.