My suspicion on CK is starting to grow more and more.
At first, when MB claimed, he said that it was a stupid claim considering his role, to which he says that he wanted to confuse the KILLER that MB is a VIP. This meant that he was somewhat sure that MB was not the killer.
But then after his defence, he flipped the other way. What I think is, he saw that MB was being targeted, and would soon be lynched.
Also, for the activity part, as
@Villain said for Rudi that he had the experience to know that staying low as a killer could get him lynched, same applies for CK too. He is also an experienced player, so he also knows that if he lays low, he would get lynched.