According to reports, a supervisor at the Reagan National Airport tower allowed an air traffic controller to end his shift early, just before the fatal collision over the Potomac River on Wednesday night.

This decision led to a situation where one controller was responsible for managing the air traffic of both airplanes and helicopters in the vicinity, as disclosed by a source familiar with the investigation to NBC News.

Normally, one controller is assigned to handle helicopters while another monitors airplanes. However, the Federal Aviation Administration (FAA) confirmed on Thursday that during the tragic crash, one air traffic controller was tasked with performing the duties of two individuals.

According to radio transmissions from Wednesday night, the lone controller warned the US Army Black Hawk that it was getting too close to the American Airlines passenger flight, which the experienced helicopter pilot acknowledged.

Experts believe the helicopter pilot may have maneuvered to avoid the wrong plane — a jet of the same model that was taking off farther away — and never saw the American Airlines flight until it was too late.

The National Transportation Safety Board is also investigating whether the chopper was flying too high.