"We've seen a tremendous escalation in violence against not only federal law enforcement, but state and local."

There was a security breach at the Chicago FBI office Thursday morning when someone jumped the fence and began throwing rocks at the building.

CHICAGO (WLS) -- It was a quiet morning at the heavily guarded FBI headquarters on Chicago's Near West Side, when in an instant, authorities say a man scaled a six-foot metal fence and began a rock attack.

Federal officers and Chicago police subdued the suspect and took him into custody.

The FBI building is set apart on West Roosevelt Road, surrounded by iron fencing and protected by security officers with weapons and scanning devices. Visitors are not even permitted to bring in cell phones. There is an extensive procedure just to get to the front door, unless you scale and jump the fence, which is what investigators say happened Thursday morning around 11 a.m.

"We've seen a tremendous escalation in violence against not only federal law enforcement, but state and local," former Chicago Deputy U.S. Marshal Ed Farrell told the I-Team.

Farrell said he has been to the building countless times over the years, adding that the facility has a "tremendous security infrastructure" and that it is nearly impossible for someone to get inside.

But outside, within the security perimeter, Thursday morning proved to be another matter.

The still unidentified man scaled the fence and vaulted over the metal grating.

Even though there were no guns or bombs, this incident in Chicago is touching raw nerves from weeks of violent threats against federal officers, agencies and buildings, following the continued January 6th prosecutions, and the FBI raid on former President Donald Trump's Florida estate.

Two weeks ago, a man in body armor carrying an AR-15 rifle, opened fire on the Cincinnati FBI Field Office with a construction nail gun, and then lead authorities on a chase and standoff. Eventually, the man died by police gunfire.

"In talking to people at the federal courthouse and other buildings, they have upped their security infrastructure, limiting doors that have access to facilities, screening people more thoroughly," said Farrell. "I think they've taken it more seriously."

There were no injuries in the rock attack, and so far no charges have been filed. The man was taken into custody and then transported to a hospital for evaluation. Authorities are working to track his history and motivation.

The FBI says there is no public threat from what happened Thursday. But experts say the incident points to a continued need for law enforcement officials to be alert for the next time, when the weapons may not simply be a bag of rocks.

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