A US defenсe source told CNN that three possible causes for the incident were being looked into: a flock of birds, drone and atmospheric anomaly. The defence source also said that the helicopters and jets that were sent to investigate the capital's airspace found nothing to support the birds' theory.
Two sources in the Capitol, however, suggested to the broadcaster that the object could have been a flock of birds since it was moving at a relatively slow pace and its image appeared and then disappeared from radar.
An air traffic control audio reviewed by CNN showed that a pilot of a responding military aircraft reported detecting a flock of birds in the airspace and said that they were going northwest.
On Tuesday, media reported that Washington airspace had been violated, leading to a temporary White House lockdown and the Capitol building being evacuated. Following the incident, the North American Aerospace Defence Command deployed fighter jets to intercept a "slow-moving blob" that caused the shutdown. Later that day, NBC News reported that the lockdown at both the White House and the Capitol had been lifted.