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.

Salvage crews have recovered an engine and large pieces of fuselage and are working to retrieve a wing from wreckage of last week’s midair collision near Washington’s Reagan National Airport.

Three U.S. Army soldiers were onboard a BlackHawk helicopter that collided with a passenger jet near Ronald Reagan Washington National Airport, U.S. officials said on Wednesday.