Auto-translated
a) Charles has a crucial opportunity to kill Beatrice on the first try; no one else can do it – the others will give them time to be found, and this is quite possible even at the end of the game.
b) Perhaps, but is there such a gap between Charles and Jane as players that the Mafia are willing to sacrifice him for the less useful Jane?
Well, never mind, this is a pointless discussion – it's obvious that Jane was the one who killed.