(CBS) – Who’s out there plotting harm to Chicago – and who’s on the lookout for them?

CBS 2 Chief Correspondent Jay Levine has a behind-the-scenes look at the war on terrorism, Chicago-style.

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After digging deep into Chicago’s counter-terrorism community, speaking with secret operatives and being briefed on quiet initiatives, not yet ready to go public, it is clear that everyone considers the threat very real.

“We are looking deep and we are looking wide,” says Robert Holley, the FBI’s Special Agent in Charge for Chicago.

Holley is legendary among FBI agents for his dogged pursuit of terrorists. He now presides over a “fortress within a fortress,” a top-secret space for his 100-strong anti-terrorism group.

He says the recent attack in Paris has yielded some lessons, given that the suspects were already on the radar of French authorities.

“I guess what we learned here is we probably need to go back, look at people we’ve looked at before to make sure nothing’s changed,” Holley says.

Chicago Police Supt. Garry McCarthy works hand in hand with Holley. The veteran of 9/11 – he was a member of the New York Police Department when the World Trade Center was attacked – thinks the threat level to the nation has increased.

He operates under the assumption, he says, that Chicago is a likely target for terrorists.

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“It could be a sporting event. It could be a building, it could be a location that a lot of people frequent,” McCarthy says.

He recalls the shooting that occurred in a Magnificent Mile shopping center around the holidays. At first, he wondered if there was an “active shooter” scenario. It turned out to be a murder-suicide.

“We have to think in those terms all the time. Our mindset has changed,” he says.

A big part of McCarthy’s counter-terrorism strategy is using the eyes and ears of his officers.

“We’ve had cases here in Chicago that were made based on a patrol officer’s off-duty observation of bizarre behavior of somebody in a city park,” he says.

It was right after the deadly Mumbai, India, hotel attack. Rogers Park resident David Headley was spotted putting his children through military-style drills on the Northwest Side.

Headley ultimately pleaded guilty to helping plan the attack in India.

“That turned in to one of the larger terrorism cases that was made in the United States,” McCarthy says.

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Both McCarthy and Holley say there are people they are watching right now. The FBI chief speaks several times a day with his counter-terrorism experts for updates.