I think its's a given that mot of the really top bods in the Empire know about the Skaven, especially given they've just concluded a war in which the Skaven played a prominent part. It is a cover-up, after all. It's pretty difficult to cover something up without getting an idea of what it actually is.a) Who has a reason to kill Valten? Well... a myriad people, Karl Franz not being the least suspect (but are you really think he would do such a thing?). However the one important reservation is that the culprit must actually know of the Skaven's existence.