How to use "favour" in a sentence

There is one important point in favour of Hutchinson's story

'You're the leader, aren't you? Can I ask you for a favour?'

'I beg you to do me one favour

I had just finished cutting some meat, which was very tough, and said, waving the knife in a way that was not at all appropriate for a vicar, that anyone who murdered Colonel Protheroe would be doing the world a favour.

'Because only the day before the crime he said that anyone who murdered Colonel Protheroe would be doing the world a favour.'