My sincere condolences to the family, and to the company.
This is second/third hand info from someone who was there.....Obviously this is not an official report.
The aircraft was run up for track and balance on the ground, the intent was NOT to fly on this run-up. The aircraft got into ground resonance, started shaking badly, and the mechanic jumped out to run away and was struck by a blade. I do not know if the mechanic shut down the engine first or not, or if the blade had detached from the aircraft.
The regulations state in part "Aircraft accident means an occurrence associated with the operation of an aircraft which takes place between the time any person boards the aircraft with the intention of flight". Therefore, technically the NTSB would not be involved.
Sections of NTSB 830 Accident reporting