If the gunshot caused as much damage as posted, (sounds like a rifled slug from a shotgun) there would have been no "moan of death". As to the gunshot, it is frankly IMPOSSIBLE to silence a supersonic round from a weapon. If she was close enough to the incident to hear a 6 lb dog moan, the gunshot would still be echoing, and that noise would cover any noise the dog made.

3:53? You're sure it wasn't 3:52? Or maybe 3:54?

Again, regardless of the common practice in the area to let dogs roam free, dogs should be kept under control. There is plenty of wildlife in the area that would think a 6 lb dog would make a nice lunch.