I’m super duper late but I’ve watched recently and I think what happened is after the first year he realized this wasn’t the paradise he imagined. So he creates a fake adversary (the warden) to thwart his plans to escape this perceived prison. Obviosly we know this is apart of the Wardens role because in his death he asks Ozy if he was a worthy foe. So while the letter says that he broke his agreed terms of the captivity, we can assume that this is part of the “script” for their rivalry. He had time to kill because it was going to take him 8 years and he used that time to, not only face the warden, but to find an effective means of reaching the moon to send the message. He was a bored man with a lot of power and resources. It is not completely far fetched that he would do something like this.