I thought about the fact that he called himself Death and died himself.
I think the murderer is Mrak. And as for Mort's role...
It's not very obvious! Half of the roles should have decent alibis; they were talking about a prince, and of course, a princess... In general, Revan is in his element when it comes to killing off roles.
Yes, I just immediately moved on to the really cool guys because searching among ordinary guests is impossible.