Brother, Emperor,
I have completed the investigation I believe and have managed to capture nearly all of the men who were part of the attack on Siegfried and his retinue. As you read this letter, they are on their way to Rome under my guard.
It seems that they were neither brigands nor assassins, but mercenaries who had been extraordinarily well equipped and paid off by a man in Florence. Luckily, the leader of the mercenaries was taken alive, and he remembers the payer to have a Bavarian accent and to be acting on behalf of another, who he did not identify.
Based on the amount paid, 60,000 florins in total, it is safe to assume that it must have been a noble with good connections or a group of nobles, as no merchant would be able to afford this amount of payment. It would probably be useful to investigate which house or noble has recently been expending much of their capital or have saved extraordinary amounts to commit to this undertaking.
Meanwhile, my agents in Ragusa have reported back to me regarding Dietrich von Dassel. While they did not bring information on his involvement with the Order, they did report that Alexander Luther is under Dassel's protection at Ragusa, spreading his heretical lies, and that Dassel is ammassing a large host loyal to his person and Luther's cause. I would suggest that you and Duke Arnold stop him immediately or allow me to intervene. It should not come to a siege as my agents have infiltrated the citadel, but still I would not wish unnecessary spilling of German blood, unless their faithlessness is proven.
With regards,
Your brother Hans