Do a bit of research and determine the published altitude restrictions for the area over the bridge for the "Low Level Route" published by the FAA. Put yourself in that helicopter at night and think about the built in risks that presents. There was plenty of discussion in the various threads that discussed the accident. A couple of pilots who operate there discussed ways to avoid complying with the Low Level route at night.
The crash occurred along the low level route that skirts National Airport (Ronald Reagan Airport). The Potomac is fairly wide at that point and hills rise up from the river on both sides. Not very high but enough to require a descent to pass along the bridge at the required height.
The major premise is there might have been a Wake Turbulence issue but seems doubtful due to the timing and vertical separation of the aircraft. There were no aircraft failures found and no marks on cranes or obstructions that pointed to a blade strike or anything like that.