Tutankhamun's mummy
Detective Michael R. King and FBI profiler Gregory M. Cooper came together with an actual Egyptologist to form their own theory which was that Tutankhamun was murdered. With the use of forensic evidence and their extensive backgrounds in criminology, they came to the conclusion that he was likely murdered by one of his closest advisors, Ay. Ay did succeed Tutankhamun on the throne, so they used that as the motivation for the murder.
Tutankhamun's mummy
The royal bloodline that Tutankhamun's family shared ended with the death of the young pharaoh, and with that came a question of the legitimacy of the following rulers. His tomb was the only one discovered that was not very disturbed by grave robbers, which allowed Carter to uncover many artifacts and the untouched mummy. It gave amazing insight into the royal burials, mummification, and tombs of the New Kingdom's 18th Dynasty. Since its discovery and widespread popularity, it has led to DNA testing done on it and other mummies from the time period that now give a proven family tree for many of the royalty during the 18th Dynasty. Since his death was unexpected and either poorly recorded or simply the records were lost over the years, with the discovery of his mummy and advances in modern technology, there is now strong and supported evidence as to Tutankhamun's death, and with that one of Egypt's most popular mysteries appears to have been solved.