(CNN)The funeral for Fox Lake, Illinois, police Lt. Joe Gliniewicz, who was fatally shot last week, is expected to draw thousands of mourners, including hundreds of police officers, to Antioch, Illinois, on Monday.
Meanwhile, the search continues for two white men and a black man who police say are suspected in the shooting.
Gliniewicz's casket arrived Monday morning at Antioch Community High School. There will be a public viewing as well as a special viewing for Gliniewicz's law enforcement colleagues ahead of the 1 p.m. CT (2 p.m. ET) service.
A procession will then head to Hillside East Cemetery, where Gliniewicz will be laid to rest. Gov. Bruce Rauner has ordered that all state and U.S. flags at government buildings be flown at half-staff until Monday evening.
Who was Joe Gliniewicz?
Authorities announced no major developments in the case over the weekend, but investigators said Friday that they had found a significant piece of evidence at the site where Gliniewicz was killed.
Lake County Major Crime Task Force commander George Filenko wouldn't specify what type of evidence was discovered, only that a person had located it.
Authorities have disclosed few details about the case, and the description of the suspects has been limited to their races and genders. Police have obtained video, but it's unclear what the footage contains.
\"Based on what we're seeing and some of the preliminary results in the videos, we're believing and going into the direction that there is somebody within the police department here or within our investigative group that's going to be able to identify these individuals,\" Filenko said.
The officer's .40-caliber pistol was found at the scene, and a source involved in the investigation said last week that Gliniewicz's gun had been fired, but it was not clear who had used it.
The last day of work
Gliniewicz was on his way to work Tuesday morning, in the cruiser he had taken home the day before, when he saw three suspicious people, Filenko said.
Gliniewicz was the type of officer who considered himself on duty as soon as he rolled into town, he said.
The lieutenant made the first call at 7:52 a.m. and called three minutes later to request backup. The backup units arrived at 8:01 and found their fellow officer dead, roughly 50 yards from his vehicle, at 8:09, Filenko said.
Authorities searched across tricky terrain and brought in helicopters, dogs, federal agents, night-vision equipment and body-heat sensors. Police cleared every building in a 2-square-mile, cordoned-off area and fielded more than 100 tips, Filenko said.
Despite the resources devoted to finding the suspects, police found no witnesses, he said.
Besides a home security video that Filenko mentioned Thursday, police said they also have one video from a truck driver who had a camera in his vehicle and was in the area Tuesday.
Remembering Lt. Joe Gliniewicz
An autopsy has been completed, but authorities haven't released the results. The Northern Illinois Police Crime Laboratory was expediting its review of evidence to determine whether there was any fingerprint or DNA transfer, Filenko said last week, but police have not divulged whether that review was complete or what it revealed.
Gliniewicz, 52, was a hero to many in Fox Lake. Hundreds gathered Wednesday night for a vigil to honor the 30-year police veteran. He led the local police explorers' program, mentoring and training youths interested in becoming officers. He was a husband and father of four.
\"Joe was my best friend and my world -- my hero,\" spouse Melodie Gliniewicz told more than 1,000 people at the candlelight vigil.
CNN's Jason Hanna, Holly Yan, Deborah Feyerick, Tina Burnside, Ryan Young and Rosa Flores contributed to this report.