Complex sentence: Everyone assumes that Grant pushed her and he is arrested on Christmas Day 1998, prompted by Beppe, who persuades Tiffany to go along with the charade that Grant has pushed her, and withholds evidence from the police that would clear Grant of wrongdoing.
Split into simpler sentences: Everyone assumes that Grant pushed her and he is arrested on Christmas Day 1998. This is prompted by Beppe, who persuades Tiffany to go along with the story that Grant pushed her; he withholds evidence that would clear Grant of wrongdoing.