Filenko said new leads have poured in throughout the day. Some come on social media. Some come on the phone. Sometimes they come when people walk into the Fox Lake police station and tell officers something they've seen.
"We feel like we are making some progress. Unfortunately, we haven't apprehended anyone," Filenko told CNN's "Anderson Cooper 360."
Lt. Joe Gliniewicz's death on Tuesday has left Fox Lake, a community of about 10,000 people in northern Illinois, with a huge void. The well-loved officer left behind a wife and four sons.
"Joe was my best friend and my world, my hero. The love of my life for the last 26 1/2 years. He was my rock as much as I was his rock," his widow, Melodie Gliniewicz, told more than 1,000 people who gathered for a candlelight vigil Wednesday evening.
More than 100 officers and federal agents are looking for three suspects in the shooting. The only description they have -- from Gliniewicz's radio calls to a dispatcher -- were two of the suspects are white and one is black.
"Based on a couple of theories that we have we believe they may have been familiar with the area where the officer eventually encountered them," Filenko said.
Gliniewicz, a 30-year police veteran,
was on his way in to work Tuesday morning, in the cruiser that he had taken home the day before, when he saw three suspicious people, Filenko told reporters earlier. This would not have been unusual as 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 about 8:09, Filenko said.
Authorities initially marked off a 2-square-mile area across tricky terrain and brought in helicopters, K-9 units, federal agents, night-vision equipment and body-heat sensors. Police cleared every home in the cordoned-off area, while fielding more than 100 tips, Filenko said.
On Wednesday, they widened the search area. Police are canvassing the area and conducting "saturation patrols" in an effort to continue the search and follow up on leads, Lake County Sheriff's Detective Christopher Covelli told reporters.
"We're going to go hand in hand with the residents of Fox Lake to ensure their safety at this time," he said.
A 17-minute timeline
So far, police have found no witnesses, but they are reviewing surveillance tapes from area buildings.
"Videos are coming from a number of places. Businesses. Factories. Gas stations," Filenko said.
They also have one video from a truck driver who had a camera in his vehicle and was in the area Tuesday.
An autopsy was completed, but authorities aren't releasing the results yet, Filenko said. The Northern Illinois Police Crime Laboratory is expediting its review of evidence to determine whether there was any fingerprint or DNA transfer.
Technicians should have that analysis finished within a "day or so," he said.
A challenging search
The FBI, U.S. Marshals and the Bureau of Alcohol, Tobacco, Firearms and Explosives joined in the hunt. More than 400 law enforcement officers raked through the heavy woods near Fox Lake on foot, all-terrain vehicles and horseback.
Hampering the search was the landscape where the manhunt unfolded. It's a mix of abandoned buildings, occupied by squatters, and residential and commercial properties situated among heavily wooded areas and a marsh. Some of the terrain is overgrown and swampy, and railroad tracks run through a portion of the area. Tuesday's intense sun didn't help matters.
Local police officers have volunteered to come in while they're off duty, and other law enforcement officers in the surrounding area have called to offer their assistance, Filenko said.
Officers were conducting a secondary review of the crime scene, "turning over every leaf and blade of grass to see if there's anything out there they may have missed," he said.
Authorities have employed 45 dogs in their search, along with six aircraft, Covelli said. Nearby residents saw SWAT teams searching yards, CNN affiliate WLS
said. Officers also went house to house looking for clues.
"I hope they catch them soon," neighbor Brenda Day said, "because I'm a single mom of three, and I'm scared."
School officials were anxious, too. Several Illinois school districts, including Fox Lake, Gavin and Big Hollow, were closed Wednesday, the Grant Community High School website said.
Asked whether he had a deadline for calling off the search, Filenko seemed to bristle at the question and responded, "I'm not going to set a time limit on this. I have a murdered colleague. ... We're not going to stop."
More than an officer
Gliniewicz's passion for police work
went far beyond what he was paid to do.
He helped lead the Fox Lake Police Department Explorer Post, which mentors young people interested in careers in law enforcement, WLS said.
, known as "G.I. Joe," was supposed to retire at the end of this month. The day before he was killed, Gliniewicz, 52, met with the mayor to discuss his retirement plans and to make sure the Explorer program continued without him, according to WLS.
"He loved his community and loved his job, and he will be very sorely missed in this community," Grant Township supervisor Catherine "Kay" Starostovic said.
Gliniewicz was an Army veteran who served in active duty and reserve from 1980 to 2007. He left the military with the rank of first sergeant.
The lieutenant is survived by a wife and four children.
His death marks the 24th time an officer has been shot and killed in the line of duty this year. Just last week, a sheriff's deputy in Houston was gunned down
while he was fueling his patrol car.
"It is a very tough time to be a police officer at this moment," CNN law enforcement analyst Cedric Alexander said. "However, these men and women that are out there doing this job, they're not going to stop doing it."