Elor and Irene were the strongest experts here, but just like everyone else, even they were finding it hard to process what Lurin no…Ruthren and Damien were talking about.
Damien didn't need Ruthren's confirmation to know the truth since no living being can have so much death aura. If experts like Elor or even Marvin had used their senses to scan the Lancaster Emperor's body, they would have figured that something seemed off and unpleasant.
Whatever Ruthren did to control a corpse wasn't perfect, unlike how Damien controlled Tristen, where the aura of death was suppressed to the maximum, making Tristen seem like a real living being.
And if any of them had carefully observed, the mannerisms and speech patterns of Ruthren clearly didn't match that of the Lancaster Emperor before. But it was already surprising that he managed to fake it a lot.