"one witness reported that the helicopter's main rotor blades broke apart as it descended through the trees."
Just a thought:
IF the pilot was descending already, (hypothesis: undertaking a "land immediately" decision if he was getting a serious control / engine / vibe problems??) THEN it would not be surprising that, going "through trees," his rotor blades upon striking the trees suffered sufficient damage to fail/fracture.
The witness report is imprecise enough to allow for a number of interpretations.
RIP.
