Complex sentence: Nearby residents of Niederanven stated that the fog at the time of the accident was very thick, so much that nearby residents couldn't see or even hear the moment of impact, even though Niederanven was in close proximity to the crash site.
Split into simpler sentences: Nearby residents of Niederanven stated that fog was present at the time of the accident. The thickness of the fog was very thick, and nearby residents couldn't see or even hear the moment of impact, even though Niederanven was in close proximity to the crash site.