The passage used is from the last scene of the first half of The Outsider. I’m sure you know it:
My whole being went tense and I tightened my grip on the gun. The trigger gave, I felt the underside of the polished butt and it was there, in that sharp but deafening noise, that it all started. I shook off the sweat and the sun. I realized that I’d destroyed the balance of the day and the perfect silence of this beach where I’d been happy. And I fired four more times at a lifeless body and the bullets sank in without leaving a mark. And it was like giving four sharp knocks at the door of unhappiness.