A new piece of "significant" evidence has been retrieved from the crime scene where a Northern Illinois police officer was killed on Tuesday, authorities who are investigating the case have revealed.

The evidence was discovered by technicians on Friday afternoon when they returned to the scene of the crime in Fox Lake Village Lake County Sheriff's Office detective Christopher Covelli said, according to the Associated Press.

Covelli did not say what the evidence was because of the ongoing investigation. "They've been going back to the scene on a daily basis with a fresh set of eyes," he said.

Police Lt. Charles Joseph Gliniewicz was killed after he tried to pursue three suspicious men on foot in the Village of Fox Lake, and the police are still on a manhunt for the suspects in the suburbs of North Chicago, as HNGN previously reported.

The manhunt expanded into the woods and swampy areas in the north of Chicago by Tuesday afternoon. Fox Lake District 114, Big Hollow District 38, Gavin District 37 and Grant High School were closed on Wednesday due to the continuing search for the suspects.

A lead investigator said on Thursday that the police obtained a video evidence of the shooting after a homeowner was able to tape the incident via his home security system. The video tape was then handed over to the Department of Homeland Security.