Well, by the looks of the pavement skid and the position at final rest it looks like there was some type of blade or transmission failure preventing or hampering autorotation. Granted a low altitude and forward motion will make that difficult too. Pops autorotated each of the 4 times he was shot down, and had the transmission scatter in one and he said that was the worst for an unscheduled dirt meeting (they were only about 100 feet up though).
I heard someone say (being interviewed) that they saw smoke, don’t know if there was a bang.
I either read or saw an interview - can’t remember which it was - of a woman who witnessed the accident and she said that she heard the engine sputtering just before the crash.