During the war : O’Brien hadn’t realized he was going to kill the man until the man was dead, all O’Brien felt was ‘sour nervousness’ he stated.
After the war : O’Brien felt as if he himself did not kill the man because his mind has still refused to come to terms with it, but he feels guilt sometimes.
a word governing, and usually preceding, a noun or pronoun and expressing a relation to another word or element in the clause, as in “the man on the platform,” “she arrived after dinner,” “what did you do it for ?”.