Complex sentence: Rossi goes to Indianapolis to continue his investigation into the two unsolved murders that have plagued him for 20 years, and he is joined by Prentiss, JJ, and Morgan when they learn about the case.
Split into simpler sentences: Rossi goes to Indianapolis in an effort to continue his investigation into the two unsolved murders that have haunted him for 20 years. He is later joined by Prentiss, JJ, and Morgan when they learn about the case.