The flight path of the "Black Hawk" helicopter before it collided with the passenger jet appears highly unusual, to say the least.

It seems there were three close encounters with other planes before the crash, and some of the helicopter's movements were erratic. 

Adding:  

In Washington, rescue workers have recovered the bodies of 28 victims from the plane crash. The search operation phase is complete, and there are likely no survivors.

This was reported by the head of the city's fire and emergency services.