(CNN) It was the type of routine call the cop known as "GI Joe" must have recounted for the young people he mentored in the village of Fox Lake, Illinois, a popular boating and fishing spot about an hour north of Chicago.

But the last radio call of his more than 30 years on the job was anything but routine. It would signal the beginning of a deepening mystery that has stumped investigators. Now the coroner says he can't rule out anything -- homicide, suicide or accident.

Gliniewicz, 52, was on his way to work September 1 in the cruiser he had taken home the day before, police said. He was the kind of cop who considered himself on duty as soon as he rolled into town.

Three suspicious men piqued his interest. The lieutenant sent word over his radio at 7:52 a.m. he was pursuing the trio on foot. Three minutes later, he requested backup. Radio communication dropped off. Colleagues would not hear Gliniewicz's voice again.

The backups arrived at about 8 a.m. and a few minutes later found Gliniewicz dead. His body was roughly 50 yards from his cruiser, police said.

Who killed Gliniewicz?

Nearly two weeks later, the investigation has yielded more questions than answers.

The mystery was compounded when investigators revealed this week that three people seen on surveillance video near the crime scene had been identified and interviewed.

"We have confirmed at this point they were not involved in this," said George Filenko, commander of the Lake County Major Crime Task Force. "Those individuals have established their whereabouts in that time frame."

Authorities said they continue to look for two white men and a black man whose behavior prompted Gliniewicz to pursue them, but they've disclosed few details. Even what was described as a significant piece of evidence found last week at the site of Gliniewicz's death remains a mystery. Filenko has declined to specify what it was.

Each new snippet of information complicates the puzzle.

A "devastating gunshot wound" to the torso killed the officer, Lake County Coroner Thomas Rudd told CNN on Thursday.

Photos: Illinois officer fatally shot Photos: Illinois officer fatally shot A police officer searches for three suspects in the fatal shooting of a police officer in Fox Lake, Illinois, on Tuesday, September 1. Hide Caption 1 of 6 Photos: Illinois officer fatally shot Police officers patrol a swampy area in Fox Lake. Hide Caption 2 of 6 Photos: Illinois officer fatally shot Police officers meet up before heading out for the search. Hide Caption 3 of 6 Photos: Illinois officer fatally shot Officers search an area for the suspects. Hide Caption 4 of 6 Photos: Illinois officer fatally shot A police officer scans an area for suspects. Hide Caption 5 of 6 Photos: Illinois officer fatally shot A police officer is led to an ambulance in the scorching heat. Hide Caption 6 of 6

And he was wearing a bulletproof vest at the time, according to two law enforcement officials briefed on the investigation. One of the officials said Gliniewicz was hit by two shots -- one stopped by his bulletproof vest, and another that entered his torso at a downward angle.

The officer's .40-caliber pistol was found at the scene, Filenko said last week. A source involved in the investigation has told CNN that Gliniewicz's gun was fired, but it's not clear who pulled the trigger.

The Lake County Sheriff's Office said Thursday that evidence indicates more than one shot was fired, but investigators can't comment on the exact number, which remains "confidential information critical to the investigation."

The coroner declined to say whether there were signs of a struggle or other wounds on Gliniewicz's body.

Rudd said he isn't ruling out a homicide, suicide or accidental death. He's still awaiting ballistics and gunshot residue evidence, fingerprints and the results of DNA tests before releasing the manner of death.

DNA evidence recovered at the crime scene did not belong to Gliniewicz, according to Filenko. About 50 people who've been interviewed in connection with the investigation have been swabbed for DNA, he said.

The Lake County Sheriff's Office later slammed the coroner for revealing details about the case.

"Doctor Rudd, releasing information which is sensitive to this investigation, puts the entire case at risk," Filenko said in a statement. "All of the progress made since this tragic incident is potentially in jeopardy."

A massive manhunt

In the days after the shooting, investigators said new leads were pouring in. Some came on social media. Others by phone. Sometimes people walked into the Fox Lake police station and simply told officers something they had seen.

Initially, authorities 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 and fielded more than 100 tips, according to Filenko.

Investigators used machetes and magnets to search the high grass at the scene of the slaying. More than 400 law enforcement officers raked through the heavy woods near Fox Lake on foot, all-terrain vehicles and horseback.

The FBI, U.S. marshals and the Bureau of Alcohol, Tobacco, Firearms and Explosives also helped in the hunt as well as police from adjoining areas. A secondary review of the crime scene involved "turning over every leaf and blade of grass to see if there's anything out there they may have missed," Filenko said.

So far, no witnesses have been found.

Gliniewicz was more than a cop

A veteran who served in active duty and reserve from 1980 to 2007, Gliniewicz was called "GI" Joe by those who knew him. He left the military with a rank of first sergeant.

And his passion for police work was evident in his leadership role with the Fox Lake Police Department Explorers Post, which mentors young people hoping to become law enforcement officers.

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"He truly loved his job," said Devan Arbay, one of Gliniewicz's Explorers.

Gliniewicz would tell his Explorers what officers went through every day, Arbay said.

"His Explorers (were) a huge part of his life," Arbay said.

Gliniewicz planned to retire last month, Chicago TV station WMAQ reported. But the police chief asked him to stay one more month.

The day before his death, Gliniewicz met with Fox Lake Mayor Donny Schmit to discuss his retirement plans and to ensure the Explorers program continued without him, CNN affiliate WLS-TV said.

'My best friend and my world'

"His commitment to the people of this community has been unmatched and will be dearly missed," the mayor said. "Not only did Fox Lake lose a family member, I lost a very dear friend."

But Gliniewicz's biggest source of pride was his family, WMAQ reported. Gliniewicz and his wife, Melodie, were married for 30 years and had four sons, including one who serves in the Army.

"Joe was my best friend and my world. My hero," Melodie Gliniewicz told more than 1,000 people at a candlelight vigil for her husband. "He was my rock as much as I was his rock."

But his death has not deterred one of his Explorers.

"It truly makes (me) want to become a police officer more and more and to fill his important work and continue doing what he did," Arbay said.