CHICAGO (Reuters) - Hundreds of police on Wednesday widened the search for three suspects in the fatal shooting of a 30-year veteran policeman in northern Illinois amid the closure of local schools and preparations for a vigil for the slain officer.

Investigators have been chasing leads, canvassing the area, collecting video evidence and reviewing information and the crime scene in the slaying of Fox Lake Police Lieutenant Charles Joseph Gliniewicz, Lake County Major Crime Task Force Commander George Filenko told reporters at a news conference.

“They’re turning over every leaf and blade of grass to see if there is anything else out there,” he said.

Filenko called the suspects “extremely dangerous.” “They shot a police officer, I think that speaks for itself.”

An autopsy of Gliniewicz, 52, was conducted on Tuesday night, Filenko said, declining to offer details.

Lake County Sheriff’s Office spokesman Christopher Covelli said the search for the suspects has broadened and nearly 400 local police officers and federal agents, more than 45 canine units and at least six aircraft have been involved.

Covelli said the manhunt had previously been contained to about 2 square miles (5.2 square km) that included incorporated and unincorporated parts of Fox Lake, located nearly 60 miles (97 km) north of Chicago and close to the Wisconsin border.

All law enforcement agencies in the surrounding area, both in Illinois and beyond, including in southern Wisconsin, are on the lookout for the suspects, Covelli said.

Covelli denied a CNN report that the search had ended, saying that the manhunt had “absolutely not” been called off.

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Gliniewicz was found wounded on Tuesday morning after reporting that he was pursuing three suspects on foot. He later died.

Officials described the three suspects as two white men and a black man.

Gliniewicz, a father of four boys and a decorated officer, was known around the village as “G.I. Joe” and was dedicated to Fox Lake and his fellow officers, Mayor Donny Schmit said.

He retired as a first sergeant in the U.S. Army Reserve and earned several awards and commendations in the police department, including a medal of valor, a Fox Lake spokesman said. Gliniewicz also had been involved in a youth law enforcement training program for about a decade.

A vigil for Gliniewicz was planned for Wednesday evening.

Filenko advised residents to remain vigilant and report suspicious activity.