After Cad Bane finds Ziro's corpse, his droid flies over to the mummified remains of Ziro's father. After looking between the mummified Hutt's arms, where Ziro had previously hidden the holo-diary containing all of the Hutt clan's secrets, the droid announces that the diary is missing. No one besides Ziro knew where the holo-novel was hidden. That was the entire reason Bane had to hunt Ziro down after his most recent escape. Even if Bane and/or the droid could deduce that it had been hidden in the tomb, they'd have no way of knowing the exact location between the mummy's arms.