Only the Judges really knew about Gramis' assasination by Vayne. And even they didnt have any concrete evidence - just strong suspicions.

Vayne would have simply said that when he arrived, he found Gramis poisoned. It would be relatively easy for him to get away with it, since he had the element of suprise and was able to plan and perhaps bribe, as well as him having new found power. Those going against him would be going against the law, and thus would be executed. (As Drace was)


About Gramis' ill condition. Its not really known how well known it is. Certainly the Judges and the Senate know of it, but whether the people knew is unknown. My earlier statement about Gramis being sick, has probably little to do with what happened though, since it was a poisoning and not a supposed death of natural causes.