(CNN) Initially hailed as a hero after his death, Fox Lake, Illinois, police Lt. Joe Gliniewicz is now likely to be remembered by another label: a betrayer.

What once appeared to be the killing of an officer in the line of duty turned out to be "a carefully staged suicide," George Filenko, Lake County Major Crimes Task Force commander, said Wednesday.

"This staged suicide was the end result of extensive criminal acts that Gliniewicz had been committing," Filenko said, announcing the conclusions of the investigation into the officer's September 1 death.

The officer had been stealing and laundering money from a police department program that mentored young people hoping to become law enforcement officers, Filenko said. Gliniewicz, a leader in that program, had been stealing money for at least seven years, he said.

The investigation found that the officer, who had experience creating mock crime scenes, staged his suicide to make it look like a homicide.

The officer placed his equipment at the scene in an "attempt to mislead first responders and investigators to believe this was a homicide," Filenko said.

'Ultimate betrayal'

Far from being a hero, Gliniewicz "committed the ultimate betrayal" with his actions over the past several years, Filenko said. "He behaved for years in a manner completely contrary to the image he portrayed."

Another reversal occurred Wednesday. A group that gave Gliniewicz's family $15,000 asked for the money back.

The 100 Club, which assists families of first responders who lose their lives in the line of duty, said it "must stay true" to the group's mission.

Gliniewicz's family didn't reply to that request but issued a statement asking for privacy as it coped "with the loss of a beloved husband and father."

Gliniewicz was well known in Fox Lake. Before becoming a police officer, Gliniewicz served active duty in the Army and Reserve from 1980 to 2007, earning the nickname GI Joe from those who knew him. He left the military with a rank of first sergeant.

The initial assumptions shifted when investigators "didn't see anything to indicate there was a struggle physically" in the officer's death, Filenko said.

Investigators then found that the village of Fox Lake, north of Chicago, had started "a thorough internal audit of all of their assets" that Gliniewicz was concerned might unearth proof of his illicit financial activities, Filenko said.

Investigators recovered 6,500 text messages Gliniewicz had deleted, Filenko said, and looked at thousands of pages of bank statements that showed financial improprieties.

"We just went where the facts took us," he said.

The investigation indicates at least two others were involved in criminal activity, though that inquiry is ongoing, and police are not commenting further for now, he said.

Authorities released text messages Gliniewicz exchanged with unidentified people in which he discussed the Explorer Post, the youth organization sponsored by the police department. Gliniewicz wanted sponsorship moved to another organization so the city administrator would not scrutinize the post finances.

"Chief won't sign off to move it to american legion and if she gets ahold of the old checking account, im pretty well f***ed," a May 13 text said.

On June 25 he advised that same person "to start dumping money into that account or you will be visiting me in JAIL!! The 1600 and the 777 all came from there..."

At Wednesday's press briefing, Filenko was asked whether police allowed the narrative of Gliniewicz to spread, even as investigators started having doubts.

"We completely believed from day one that (the death of Gliniewicz) was a homicide," he said. "Our intention was never to mislead the public."

The last call

Gliniewicz was under increasing levels of stress from scrutiny into what the investigators found to be criminal activity, Filenko said.

The veteran officer had planned to retire in August, but he was asked to stay on for another month.

The last radio call of his more than 30 years on the job was anything but routine. It would signal the beginning of a mystery that stumped investigators for a time.

On the morning of September 1, the lieutenant sent word over his radio at 7:52 that he was pursuing a trio on foot. Three minutes later, he requested backup. Radio communication dropped off. Colleagues would not hear Gliniewicz's voice again.

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

Three people who appeared in a surveillance video near the crime scene were cleared of suspicion.

The shooting

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

The officer's .40-caliber pistol was found at the scene. A source involved in the investigation told CNN in September that Gliniewicz's gun was fired, but it wasn't clear who pulled the trigger.

Lake County officials said the case was being handled as a homicide, but other theories remained on the table during the investigation, including the possibility of a self-inflicted fatal gunshot wound.

The coroner said he couldn't rule out a homicide, suicide or accident.

A massive manhunt was launched in the aftermath.

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. But eventually they pulled out, saying no suspects or persons of interest had been identified.