Analysis of the debris field will determine if all of the major components were present....all main rotor blades, tail rotor blades, gear boxes, drive shafts, and thus rule out loss of those in-flight.
Engine and gearbox examinations will determine if they were operating at the time of impact with the water.
Hopefully, the CVR/FDR if installed and still functional will generate other information that will point to a cause.
One thing is for sure....that aircraft hit the water with a great deal of force and very suddenly.