Just offshore of the towering national monuments of Washington, a tall crane now hovers over the Potomac River. It casts a large shadow over the effort to understand what caused the collision of a passenger jet and a military helicopter last Wednesday as a new phase of the recovery starts.

Recovery crews could be seen pulling the American Airlines' plane wreckage out of Washington DC's Potomac River on Monday. Sixty passengers and four crew members were on the American Airlines flight and three soldiers on the Black Hawk helicopter.