Why was Tutankhamum's life so mysterious?

After I watched the film, The Curse of King Tut's Tomb, I get some ideas why Tutankhamum's life so mysterious.

I think it is mysterious because nobody really knows why he died at the age of nineteen. There was no record in Egyptian history about the reason of his death. But there were a lot of treasures in his tomb. It made the whole story more mysterious after the tomb was found but there was something strange happened afterward ...