Complex sentence: The level of music was so high, that Olga's grandmother called the local sherrif, upon arriving he recognises Belov's face from the Wanted poster and immediately calls for OMON police to come.
Split into simpler sentences: The level of music was so high, that Olga's grandmother called the local sheriff. Upon arriving, he recognises Belov's face from the Wanted poster and immediately calls for OMON police to come.