Complex sentence: At the same time the Mafia killed police superintendent Boris Giuliano in Palermo; he was investigating the Mafia's heroin trafficking and had contacted Ambrosoli just two weeks before to compare investigations.
Split into simpler sentences: At the same time the Mafia killed police superintendent Boris Giuliano in Palermo. He was investigating the Mafia's heroin trafficking and had contacted Ambrosoli just two weeks before to compare investigations.