Investigators in northern Illinois say they're hopeful a video and crime lab results will produce a break in the hunt for three men wanted in this week's fatal shooting of a police officer. A guide to key aspects of the case:

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THE SLAYING

Lt. Charles Joseph Gliniewicz, a 30-year police veteran who was on the cusp of retiring, was shot Tuesday in the village of Fox Lake while pursuing three suspicious men, authorities say. He told dispatchers the three ran into a swampy area and requested a second unit. Dispatchers soon lost contact with him, and backup officers found him about 50 yards from his squad car with a gunshot wound. He died soon after.

The killing occurred in an open area of trees and marshland bordered by several houses on one end and a public works site on the other. Police say they've previously received several complaints about vandalism and squatters in the area, but it was not clear what brought Gliniewicz to the scene Tuesday.

Fox Lake is about 45 miles north of Chicago.

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WHAT'S NEXT?

For three days, authorities have had only a vague description of the men that Gliniewicz radioed in to dispatchers: Two are white, the other is black.

But the lead investigator revealed Thursday that a resident who lives near the shooting scene had come forward with video from a home security system that the homeowner says shows three men.

The video had to be sent to the federal Department of Homeland Security because it's on a hard drive that requires special technology for retrieval, so authorities don't expect to get a look until Friday. Authorities also expect results Friday of crime lab analysis of everything recovered from the scene.

Lake County Major Crime Task Force Cmdr. George Filenko said Thursday that investigators were also pursuing another angle, but he was not ready to provide details.

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CHASING LEADS

Filenko says investigators are getting so many tips by phone, email and social media that a second detective has been tasked with filtering through them. Authorities believe there's a strong possibility the suspects are still in the general area, and detectives are depending on the public's help.

"All it takes is one tip or good lead to break a case wide open," Filenko said Wednesday.

Filenko has more than 100 people actively deployed to investigate on the ground. They are going back to nearby homes to interview residents, sometimes two or three times.

During the manhunt, patrols have also searched cabins, barns and forests that dot the rural landscape and its many forest preserves.

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NERVES RATTLED

Fox Lake is nestled in one of the state's most popular recreational areas, a boating and fishing playground known as the Chain O' Lakes. It's especially busy during Labor Day weekend, usually drawing tens of thousands of visitors.

But concerns mounted that tourists might decide to go elsewhere because of the heavy police presence and fear that the fugitives could be hiding somewhere among the lakes, wetlands and forest glens.

"People are concerned about those individuals. And the few customers I get in here, that's all they talk about," said Marciano Martinez, co-owner of the popular Dockers restaurant.

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MOURNING A POPULAR OFFICER

Gliniewicz, a 52-year-old tattooed officer with a shaved head, was known around town as "G.I. Joe." Beyond his decades-long career in law enforcement, he was also a mentor and role model in the community, having led a police Explorers post for four years.

Gliniewicz was planning to retire at the end of the month and had just met Monday with the mayor to ensure that the Explorer post would go on.

His funeral will be 1 p.m. Monday at Antioch High School, northeast of Fox Lake.