Oh bother! I will have to explain a bit about the political situation in Persia at the time, which was about 530 BCE as you calculate time. The King of Kings, Cyrus the Great, was dead. He had two sons, Cambyses and Bardiya. It seemed no clear thing which prince would rule, so the magi were to decide. I needed to work on this, for the next king would be my vessel.
Having found what I thought was a competent helper I left my body and examined them in turn. I saw that Bardiya was a guileless simpleton. He actually had very little ambition for the throne, but it seemed that he was the favorite of the magi. I think it was because they believed they could control him. Now, for me to be successful in possessing someone, I must discover that person’s greatest fear, or in some cases, guilt.
Cambyses was ambitious and ruthless. I decided to make him the next king. I would accomplish this by having him murder his own brother. First I had to get into his head. If you recall, Cyrus the Great had a splendid building in the middle of his great garden. It was called the Quiet Room. As far as anyone else knew, it was a place of meditation. We all know, however, that he used this room to relieve himself of the human waste products he never let anybody know he had.
I explained previously that Cyrus took great pride in being beyond mortal—a god on earth. A Greek visitor noted that the king was indeed a god, for he had no bodily needs. This Quiet Room had been prepared for the king by his royal builder, who was the only one who knew of its function, until Cyrus had him killed. Now after the death of Cyrus, his ghost was anxious. He appeared to Mihr, his advisor, and told him that the room must be demolished totally, without anyone ever entering it. He made these wishes known to the court.
Prince Bardiya agreed immediately, but Cambyses, thinking that it was the place of hoarded treasure, wanted to take first whatever he found there. The magi prevailed, and Cambyses was sorely disappointed and angry. He decided to raid the place secretly.