He changes from "I must kill him" to merely being a witness to the dead foe.
The second still means "I must kill him." It's less blunt and more flowery, but someone who tells you the latter is still planning to be the one holding the knife.
No, it doesn't necessarily mean that. It can mean that, but he could just as easily have someone else kill the person on his behalf as he can himself.
Moreover, there is also another element that I missed: the implied need that comes from the word "must". There is no such thing in the second one unless you read the "at all costs" thing in that way, but that is still a different meaning.
The second still means "I must kill him." It's less blunt and more flowery, but someone who tells you the latter is still planning to be the one holding the knife.
No, it doesn't necessarily mean that. It can mean that, but he could just as easily have someone else kill the person on his behalf as he can himself.
Moreover, there is also another element that I missed: the implied need that comes from the word "must". There is no such thing in the second one unless you read the "at all costs" thing in that way, but that is still a different meaning.