Complex sentence: Demopoulos found out that he had been named co-executor in an earlier will and challenged Lafferty's appointment, claiming that convicted felon Tammy Payette told him (Demopoulos) that Lafferty had killed Duke.
Split into simpler sentences: Demopoulos found out that he had been named co-executor in an earlier will and challenged Lafferty's appointment. It seems that convicted felon Tammy Payette alleged that Lafferty had killed Duke.