BALTIMORE (WJZ) — In a massive, multi-agency drill, local law enforcement, fire, and EMS practiced how they will respond to a potentially deadly situation.

There were six staged terrorist attacks as the massive training exercise spanned three state lines and involved hundreds of emergency responders.

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Police say they drill every year for potential terrorist attacks. What sets this exercise apart was the multiple locations and agencies training together.

WJZ’s Kimberly Eiten was there as authorities rolled out to neighborhoods across Maryland, Virginia, and Washington D.C. to respond to simulated terrorist attacks.

“We need to continue to exercise to be prepared for the known or the unknown,” said Chuck Bean, with the Metropolitan Washington Council of Governments.

The unknown in this case was a coordinated attack near the Capitol involving multiple targets and teams of terrorists.

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Wednesday morning, WJZ watched responders rush to the staged scenes in full force.

Everything from unmarked police cars, to armored vehicles, to a mobile command unit, were used in this drill, but what their role will be, by design, is a mystery.

A mystery, because when, where, and how an attack could happen is unpredictable, but Maryland National Capital Park Police Chief Stanley R. Johnson says the response won’t be.

“We want to make sure we can respond effectively and efficiently,” Johnson said.

A warning for people who live in southern Maryland and near the Capitol if you saw a large police presence in your neighborhood Wednesday, it may have been tied to this exercise.

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