Complex sentence: Jeff finally confesses that he was involved in Donna Mauer's death, but that he only watched while his accomplice committed the murder; he promises that, if she spares his life, he will disclose the other man's name and help her find him.
Split into simpler sentences: Jeff finally confesses that he was involved in Donna Mauer's death but that he only watched while his accomplice committed the murder. He promises that, if she spares his life, he will disclose the other man's name and help her find him.