Possible causes?
An awful tragedy, but one that the NTSB should be able to resolve in a fairly simple way, with the pilot and some of the passengers surviving.
I heard there were gusts, but not their strength. Gusts could have done to this Bell 206 what it did to the UK based EC 120 I flew earlier this year (see heli down at Redhill thread) - a variant of LTE.
Alternatively I have experienced tail rotor driveshaft bearing failure in certain Bell machines - with tell tale evidence.
Either way, I hope the survivors continue to recover, and an NTSB report is issued without delay.