The evacuation of the Capitol staff on Wednesday was carried out because of a plane with members of the US Army Golden Knights parachute squad, heading from the Andrews military base, Maryland, to the Nationals Park stadium in Washington, where the paratroopers were supposed to perform before a baseball game, the Associated Press reported.

According to it, the Capitol police alerted employees to the threat when the plane circled within the closed airspace near the Capitol building complex. According to the radar tracking, the plane was all the time outside the closed airspace directly above the Capitol, the AP notes.

Sources told the agency that investigators are still investigating why the plane's flight was not properly coordinated with law enforcement officials in Washington. Interlocutors of the agency noted that, according to preliminary data, the pilot probably did not report the takeoff properly or did not have the appropriate permission.

Reuters reported that the US Federal Aviation Administration would conduct an investigation.