ROUND LAKE BEACH, Ill. -- A police officer who was lauded as a hero after his fatal shooting triggered a costly manhunt in fact killed himself because he was about to be exposed as a thief and carefully staged his death to make it seem as if he died in the line of duty, authorities said Wednesday.

Fox Lake Police Lt. Charles Joseph Gliniewicz embezzled thousands of dollars from the town's 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," Filenko said. He declined to provide more details about the crimes, because "the investigation strongly suggests criminal activity on the part of at least two other individuals."

The commander then took 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."

Minutes before he died Sept. 1, Gliniewicz radioed he was chasing three suspicious men in a swampy area of Fox Lake, a suburb north of Chicago. Backup officers followed a trail of equipment to the Army veteran's body, about 50 yards from his squad car.

Gliniewicz was a 30-year police veteran and expert crime-scene investigator, his boss said, and took elaborate steps to try to make it appear he died in a struggle. The first bullet struck his cell phone and ballistic vest. The second pierced his upper chest, and his head was bruised in ways the coroner said could have been intentional. His handgun wasn't found for more than an hour, although it was less than three feet from the body, Filenko said.

A manhunt began immediately, with hundreds of officers searching houses, cabins and boats on area lakes. About 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 the Daily Herald newspaper published in early October.

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

Dr. Thomas Rudd announced Gliniewicz was killed by a "single devastating" shot to his chest, and he couldn't rule out suicide or an accident. That prompted an angry response from Filenko, who said releasing such details put "the entire case at risk."

But Filenko said Wednesday as the case progressed, investigators uncovered incriminating texts and Facebook messages Gliniewicz had sent, expressing fears as early as May 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***ed," the first message reads.

He had deleted those texts, but authorities managed to recover them anyway.

Investigators released some of the texts 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 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 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 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 solid alibis, Filenko said, and no one ever was 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. 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.