Three scenarios come immediately to mind: There were thunderstorms reported in the area, a possible microburst; the chopper had just refueled at the Las Vegas airport (but had also done so earlier too); or shot down by local redneck idiot (another was shot at in ABQ a couple of years ago).
BCSO has excellent pilots. Their other chopper helped suppress a wildfire just east of the range where I worked a few years back. They could drop on a specific tree if it flared up. I’m thinking weather or some massive mechanical failure. It had to happen very fast for there was no mayday call.