CHICAGO (CBS) — One month after a Fox Lake police officer was shot and killed in a marshy area of the northern suburb, police confirmed for the first time that Lt. Charles Joseph Gliniewicz was shot twice with his own weapon.

Lake County Major Crimes Task Force Cmdr. George Filenko said Gliniewicz was shot once on the right front side of his protective vest, and once in the upper chest. Also for the first time, Filenko revealed testing found gunshot residue on Gliniewicz’s hands, but said those tests were inconclusive in determining whether Gliniewicz fired the weapon, or if his hands simply were near the gun when it was shot.

“In layman’s terms the weapon could have been fired by Lieutenant Gliniewicz, or he could have been in close proximity to the weapon being fired,” Filenko said.

Filenko said, according to the coroner’s report in the case, the first shot – which struck Gliniewicz’s vest – would have hit him with force similar to a sledgehammer. The second shot missed his vest, and struck him in the upper left chest, killing him, according to Filenko.

Gliniewicz, 52, was shot and killed on Sept. 1, near U.S. Route 12 and Sayton Road in Fox Lake. Police have said he was investigating suspicious activity in the area, and radioed that he had begun chasing three suspects. A few minutes after backup officers arrived on the scene, they found his body.

Police have said Gliniewicz provided only a very vague description of the three suspects – two white males and one black male. While authorities have not determined the manner of his death, investigators are treating the case as a homicide, but have not ruled out any other possibility.

Filenko said investigators found indications of a struggle at the scene, but would not elaborate. He also said they found nine unknown DNA samples at the scene, three of which met the requirements to be entered into the national Combined DNA Index System. One of those samples has been confirmed as a male, FIlenko said.

Police have taken 100 DNA swabs from various people as part of the investigation, including anyone interviewed in connection with the case, and anyone who had direct or indirect contact with Gliniewicz, or who was near the crime scene on that day – including every police officer who was close to the scene.
Filenko said additional DNA swabs were being collected Thursday, and 30 to 40 samples were being sent to the Illinois State Police crime lab for comparison.

Authorities have released few other details in the case, saying they don’t want to compromise the investigation or any potential prosecution.