The pilot is literally the one who holds most of the blame here.

This is a pilot-error accident. They flew a perfectly functioning airplane into rising terrain on a visual approach.

The pilot requested, and was cleared for, a visual approach. Among other things that that imposes upon on the pilot is an obligation to maintain visual contact with the airport (or the preceding aircraft to follow, not applicable here) and to maintain terrain and obstacle clearance.

The primary probable cause will be found to be something like "The pilot’s failure to maintain clearance from terrain while on visual approach." with additional notes of "Contributing to the accident were the dark moonless night, the NOTAM'd unreliability of GPS signal in the area which required the crew to revert to other navigation methods, and the pilot's decision to fly an unaided visual approach rather than flying the ILS instrument approach track."

The passengers were blameless, but the flight crew was not.