I had an interesting conversation with a former Navy helicopter pilot today. When I saw that helicopter pitch down, it looked just like a plane whose wings had suddenly stalled. According to the pilot, this is a fairly good possibility for what caused that crash. A rotor blade is just an airfoil and any airfoil will stall if its angle of attack gets too high. The helicopter was hovering at a high altitude, so the rotor pitch was already pretty high. They were hoisting up a dead body when the accident happened and the additional weight would've required the pilot to increase the pitch some more. That alone or perhaps coupled with a cyclic control input (which further increases the angle of attack) might've been enough to cause a rotor stall. It's too soon to tell but that is a candidate cause.