ROUND LAKE BEACH, Ill. -- A northern Illinois police officer who was lauded as a hero after his fatal shooting triggered an intense and costly manhunt in fact committed suicide, carefully staging his death because he was about to be exposed as a thief, authorities said Wednesday.

Fox Lake Police Lieutenant Joe Gliniewicz embezzled thousands of dollars from the Fox Lake Police Explorer program for seven years, and spent the money on such things as mortgage payments, travel expenses, gym memberships and adult websites, Lake County Major Crimes Task Force Commander George Filenko said.

"We have determined this staged suicide was the end result of extensive criminal acts that Gliniewicz had been committing in fact he was under increasing levels of personal stress from scrutiny of his management of the Fox Lake Police Explorer program," Filenko said.

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The commander then endured blistering questions from skeptical journalists about his handling of the two-month investigation.

"We completely believed from day one that this was a homicide," Filenko said. "Gliniewicz committed the ultimate betrayal."

Just before he died, Gliniewicz radioed that he was chasing three suspicious men in a swampy area near Fox Lake, a suburb north of Chicago. Backup officers later found the Army veteran's body about 50 yards from his squad car. His handgun wasn't found for more than an hour, even though it was less than three feet from the body, Filenko said.

Fox Lake Lieutenant Charles Joseph Gliniewicz is pictured in this undated handout photo provided by Lake County Sheriff's Office in Illinois, September 1, 2015. REUTERS

Lake County Sheriff's Office spokesman Christopher Covelli called the investigation "extraordinarily complex," saying investigators had reviewed 6,500 pages of text messages from Gliniewicz's phone and 40,000 emails. More than 200 pieces of evidence were submitted to crime labs.

Filenko said detectives wanted to be certain before releasing a definitive conclusion and that they only arrived at that point about a week and a half ago.

He said, "We don't jump to conclusions. We go where the facts lead us."

Gliniewicz's death on Sept. 1 set off a large manhunt, with hundreds of officers searching houses, cabins and even boats on area lakes. Helicopters with heat-sensing scanners and K-9 units scoured the area for days. Some 50 suburban Chicago police departments and sheriff's offices assisted, racking up more than $300,000 in overtime and other costs, according to an analysis that the Daily Herald newspaper published in early October.

More than 100 people submitted to DNA tests as investigators sought matches to evidence collected at the crime scene - genetic tests that Filenko said ultimately found nothing. Asked Wednesday whether that evidence will now be destroyed, Filenko said he didn't know.

More than 100 investigators stayed on the case for weeks, even as questions arose and investigators began to concede that they could not rule out suicide or an accident. One hint came when Rudd announced that Gliniewicz was killed by a "single devastating" shot to his chest, prompting an angry response from Filenko, who said releasing such details put "the entire case at risk."

But Filenko revealed Wednesday that as the case progressed, investigators were uncovering incriminating texts and Facebook messages Gliniewicz had sent, expressing fears as early as May that his thefts were about to be exposed by an audit of the Explorer program being conducted by a new village administrator.

"If she gets ahold of the old checking account, im pretty well f(asterisk)(asterisk)(asterisk)ed," the first message reads.

A Fox Lake resident placed this sign at the police department which was once a memorial of flowers for Joe Gliniewicz. Ryan Corsaro/CBS News

He had deleted the texts, but authorities were able to recover them anyway. Investigators released some of them verbatim, but did not identify the people he sent them to.

"This village administrator hates me and explorer program," he said in another. "This situation right here would give her the means to CRUCIFY ME (if) it were discovered."

On Aug. 31, the day before he killed himself, Gliniewicz wrote that the administrator had demanded a complete inventory and financial report on the program.

Village Administrator Anne Marrin read a brief statement Wednesday thanking authorities for their work, and noting that the officer threatened her personally after she began asking tough questions.

In one of the texts, Gliniewicz and "Individual #2" discuss trying to get Marrin out of office, perhaps by arresting her for drunk driving, or worse. "Trust me ive thougit through MANY SCENARIOS from planting things to the volo bog," he wrote, referring to a local waterway that would be difficult to search.

To the public, the case remained a homicide investigation, even after authorities announced in October that Gliniewicz, 52, had been shot with his own weapon.

Authorities released only the vague description of three suspects that Gliniewicz had radioed in - two white men and a black man. They tracked down three men captured on a home security video system, but all had rock solid alibis, Filenko said, and no one was ever arrested.

Gliniewicz was held up on national television as a hero who died doing his job in a dangerous environment. An outpouring of grief swept Fox Lake, a village of 10,000 about 50 miles north of Chicago. The officer's picture was hung in storefront windows and flags flew at half-staff in his honor. Others described him as tough when needed, but also as sweet and a role model to youngsters aspiring to go into law enforcement.

Gliniewicz's family had dismissed the suggestion of suicide. The tattooed officer with a shaved head, who was married and had four children, "never once" thought of taking his own life, and was excited about his retirement plans, his son D.J. Gliniewicz said.