They were known to use distinctive arrows in combat. If the Natives were victorious in battle, they would take the severed heads from their opponents as victory trophies.[OOG 2]
When Prince Attrebus was kidnapped, his kidnappers cut the head of one of his bodyguards and they dressed him with the prince's robes, including the signet ring of the Crown Prince. They also beheaded the corpses of other bodyguards and they left arrows pertaining to the Natives in order to incriminate them.[OOG 1]
Inspector Colin was assigned the case. He suspected that Attrebus hadn't been really murdered by the Natives, so he confessed to the Emperor that his son might be alive. Colin was later proved to be right.