7:29 PM ET

The U.S. Capitol was briefly evacuated Wednesday evening after police identified an aircraft that they said posed a probable threat, but the plane was actually carrying members of the U.S. Army Golden Knights.

Nationals Park is a little more than a mile away from the U.S. Capitol and is home to the Nationals.

Two people familiar with the matter told The Associated Press that investigators were still trying to figure out why the event wasn't properly coordinated. As the plane circled overhead, federal agencies began to scramble.

The capital region is protected by several surface-to-air missile sites, as well as military aircrews on round-the-clock alert. It didn't appear that any of those systems were scrambled.

A plane carrying members of the U.S. Army Golden Knights for a pregame demonstration at Nationals Park prompted a brief evacuation of the U.S. Capitol Wednesday evening. AP Photo/Alex Brandon

The pilot may have not reported taking off or had appropriate clearance according to the people.

The alert from the U.S. Capitol Police sent congressional staffers fleeing from the Capitol and legislative building.

The aircraft, a twin-engine plane, took off from Joint Base Andrews in Maryland and had been circling in heavily restricted airspace close to the Capitol when the alert was sent. The plane, a De Havilland Twin Otter, remained clear of the prohibited airspace over the Capitol Building and other government complexes at all times. The army plane is coordinating its flight with the control tower at Ronald Reagan Washington National Airport.

After the parachuters descended into the field at Nationals Park, the plane came back to Andrews.

Information from The Associated Press was included in the report.