Complex sentence: Hennessy's killing became the first widely publicized Mafia incident in the United States, and resulted in hundreds of baseless arrests of newly arrived Italian immigrants and a major trial in 1891 in New Orleans in which 19 people were indicted.
Split into simpler sentences: Hennessy's killing became the first widely publicized Mafia incident in the United States. There was a major trial in 1891 in which 19 people were indicted.